diff --git a/.editorconfig b/.editorconfig
new file mode 100644
index 000000000..67289a444
--- /dev/null
+++ b/.editorconfig
@@ -0,0 +1,37 @@
+# https://editorconfig.org
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+indent_style = space
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.rb]
+# Required since we use heredocs to assert against Hatchet output, and sometimes that output
+# contains trailing newlines. Our RuboCop config ensures these are only allowed in heredocs.
+trim_trailing_whitespace = false
+
+[*.sh]
+binary_next_line = true
+# We sadly have to use tabs in shell scripts otherwise we can't indent here documents:
+# https://www.gnu.org/software/bash/manual/html_node/Redirections.html#Here-Documents
+indent_style = tab
+shell_variant = bash
+switch_case_indent = true
+
+# Catches scripts that we can't give a .sh file extension, such as the Buildpack API scripts.
+[**/bin/**]
+binary_next_line = true
+indent_style = tab
+shell_variant = bash
+switch_case_indent = true
+
+# The setup-ruby GitHub Action creates this directory when caching is enabled, and if
+# it's not ignored will cause false positives when running shfmt in the CI lint job.
+[vendor/bundle/**]
+ignore = true
+
+[Makefile]
+indent_style = tab
diff --git a/.github/CODEOWNERS b/.github/CODEOWNERS
index 52082f8a2..3f4e003a1 100644
--- a/.github/CODEOWNERS
+++ b/.github/CODEOWNERS
@@ -1,8 +1,12 @@
 # Default to requesting pull request reviews from the Heroku Languages team.
+#ECCN:Open Source
+#GUSINFO:Heroku - Languages,Heroku Python Platform
 * @heroku/languages
 
 # However, request review from the language owner instead for files that are updated
 # by Dependabot or release automation, to reduce team review request noise.
 CHANGELOG.md @edmorley
 Gemfile.lock @edmorley
+/.github/workflows/ @edmorley
+/builds/Dockerfile @edmorley
 /requirements/ @edmorley
diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index 366df6035..636065174 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -13,6 +13,14 @@ updates:
         update-types:
           - "minor"
           - "patch"
+  - package-ecosystem: "docker"
+    directory: "/builds"
+    schedule:
+      interval: "monthly"
+    labels:
+      - "dependencies"
+      - "docker"
+      - "skip changelog"
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule:
@@ -28,3 +36,9 @@ updates:
     labels:
       - "dependencies"
       - "python"
+    groups:
+      # We don't limit grouping for Python to just minor/patch versions, since pip doesn't follow
+      # semver, plus having to update CHANGELOG.md means it's easier to just have a single PR.
+      python-dependencies:
+        patterns:
+          - "*"
diff --git a/.github/workflows/build_python_runtime.yml b/.github/workflows/build_python_runtime.yml
index 76812cb75..6039a5710 100644
--- a/.github/workflows/build_python_runtime.yml
+++ b/.github/workflows/build_python_runtime.yml
@@ -5,7 +5,7 @@ on:
   workflow_dispatch:
     inputs:
       python_version:
-        description: "Python version (eg: 3.12.0)"
+        description: "Python version (eg: 3.13.0)"
         type: string
         required: true
       stack:
@@ -13,9 +13,9 @@ on:
         type: choice
         options:
           - auto
-          - heroku-20
           - heroku-22
           - heroku-24
+          - heroku-26
         default: auto
         required: false
       dry_run:
@@ -36,14 +36,14 @@ env:
 # Unfortunately these jobs cannot be easily written as a matrix since `matrix.exclude` does not
 # support expression syntax, and the `matrix` context is not available inside the job `if` key.
 jobs:
-  heroku-20:
-    if: inputs.stack == 'heroku-20' || inputs.stack == 'auto'
+  heroku-22:
+    if: inputs.stack == 'heroku-22' || inputs.stack == 'auto'
     runs-on: pub-hk-ubuntu-24.04-xlarge
     env:
-      STACK_VERSION: "20"
+      STACK_VERSION: "22"
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v7
       - name: Build Docker image
         run: docker build --platform="linux/amd64" --pull --tag buildenv --build-arg=STACK_VERSION builds/
       - name: Compile and package Python runtime
@@ -57,41 +57,43 @@ jobs:
         if: (!inputs.dry_run)
         run: aws s3 sync ./upload "s3://${S3_BUCKET}"
 
-  heroku-22:
-    # On Heroku-22 we only support Python 3.9+.
-    if: inputs.stack == 'heroku-22' || (inputs.stack == 'auto' && !startsWith(inputs.python_version,'3.8.'))
-    runs-on: pub-hk-ubuntu-24.04-xlarge
+  heroku-24:
+    if: inputs.stack == 'heroku-24' || inputs.stack == 'auto'
+    strategy:
+      fail-fast: false
+      matrix:
+        arch: ["amd64", "arm64"]
+    runs-on: ${{ matrix.arch == 'arm64' && 'pub-hk-ubuntu-24.04-arm-xlarge' || 'pub-hk-ubuntu-24.04-xlarge' }}
     env:
-      STACK_VERSION: "22"
+      STACK_VERSION: "24"
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v7
       - name: Build Docker image
-        run: docker build --platform="linux/amd64" --pull --tag buildenv --build-arg=STACK_VERSION builds/
+        run: docker build --platform="linux/${{ matrix.arch }}" --pull --tag buildenv --build-arg=STACK_VERSION builds/
       - name: Compile and package Python runtime
         run: docker run --rm --volume="${PWD}/upload:/tmp/upload" buildenv ./build_python_runtime.sh "${{ inputs.python_version }}"
       - name: Test Python runtime
         run: |
           RUN_IMAGE='heroku/heroku:${{ env.STACK_VERSION }}'
-          ARCHIVE_FILENAME='python-${{ inputs.python_version }}-ubuntu-${{ env.STACK_VERSION }}.04-amd64.tar.zst'
+          ARCHIVE_FILENAME='python-${{ inputs.python_version }}-ubuntu-${{ env.STACK_VERSION }}.04-${{ matrix.arch }}.tar.zst'
           docker run --rm --volume="${PWD}/upload:/upload:ro" --volume="${PWD}/builds:/builds:ro" "${RUN_IMAGE}" /builds/test_python_runtime.sh "/upload/${ARCHIVE_FILENAME}"
       - name: Upload Python runtime archive to S3
         if: (!inputs.dry_run)
         run: aws s3 sync ./upload "s3://${S3_BUCKET}"
 
-  heroku-24:
-    # On Heroku-24 we only support Python 3.10+.
-    if: inputs.stack == 'heroku-24' || (inputs.stack == 'auto' && !startsWith(inputs.python_version,'3.8.') && !startsWith(inputs.python_version,'3.9.'))
+  heroku-26:
+    if: inputs.stack == 'heroku-26' || inputs.stack == 'auto'
     strategy:
       fail-fast: false
       matrix:
         arch: ["amd64", "arm64"]
     runs-on: ${{ matrix.arch == 'arm64' && 'pub-hk-ubuntu-24.04-arm-xlarge' || 'pub-hk-ubuntu-24.04-xlarge' }}
     env:
-      STACK_VERSION: "24"
+      STACK_VERSION: "26"
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v7
       - name: Build Docker image
         run: docker build --platform="linux/${{ matrix.arch }}" --pull --tag buildenv --build-arg=STACK_VERSION builds/
       - name: Compile and package Python runtime
diff --git a/.github/workflows/check_changelog.yml b/.github/workflows/check_changelog.yml
index e528aae03..ee511b3d2 100644
--- a/.github/workflows/check_changelog.yml
+++ b/.github/workflows/check_changelog.yml
@@ -13,7 +13,7 @@ jobs:
     if: (!contains(github.event.pull_request.labels.*.name, 'skip changelog'))
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v7
       - name: Check that CHANGELOG is touched
         run: |
           git fetch origin ${{ github.base_ref }} --depth 1 && \
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index ed5588b7d..35de00fb4 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -10,19 +10,27 @@ on:
 permissions:
   contents: read
 
+env:
+  # Used by shfmt and more.
+  FORCE_COLOR: 1
+
 jobs:
   lint:
     runs-on: ubuntu-24.04
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v7
       - name: Install Ruby and dependencies
         uses: ruby/setup-ruby@v1
         with:
           bundler-cache: true
-          ruby-version: "3.3"
+          ruby-version: "4.0"
       - name: Run ShellCheck
         run: make lint-scripts
+      - name: Run shfmt
+        uses: docker://mvdan/shfmt:latest
+        with:
+          args: "--diff ."
       - name: Run Rubocop
         run: bundle exec rubocop
 
@@ -31,24 +39,24 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        stack: ["heroku-20", "heroku-22", "heroku-24"]
+        stack: ["heroku-22", "heroku-24", "heroku-26"]
     env:
-      HATCHET_APP_LIMIT: 200
+      HATCHET_APP_LIMIT: 300
       HATCHET_DEFAULT_STACK: ${{ matrix.stack }}
       HATCHET_EXPENSIVE_MODE: 1
       HEROKU_API_KEY: ${{ secrets.HEROKU_API_KEY }}
       HEROKU_API_USER: ${{ secrets.HEROKU_API_USER }}
       HEROKU_DISABLE_AUTOUPDATE: 1
-      PARALLEL_SPLIT_TEST_PROCESSES: 60
-      RSPEC_RETRY_RETRY_COUNT: 3
+      PARALLEL_SPLIT_TEST_PROCESSES: 90
+      RSPEC_RETRY_RETRY_COUNT: 1
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v7
       - name: Install Ruby and dependencies
         uses: ruby/setup-ruby@v1
         with:
           bundler-cache: true
-          ruby-version: "3.3"
+          ruby-version: "4.0"
       - name: Hatchet setup
         run: bundle exec hatchet ci:setup
       - name: Run Hatchet integration tests
@@ -57,17 +65,12 @@ jobs:
 
   container-test:
     runs-on: ubuntu-24.04
-    defaults:
-      run:
-        # Work around lack of TTY causing errors when using `docker run -it`:
-        # https://github.com/actions/runner/issues/241
-        shell: 'script -q -e -c "bash -eo pipefail {0}"'
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v7
       # These test both the local development `make run` workflow and that `bin/report` completes successfully
       # for both passing and failing builds (since `bin/report` can't easily be tested via Hatchet tests).
       - name: Run buildpack using default app fixture
         run: make run
       - name: Run buildpack using an app fixture that's expected to fail
-        run: make run FIXTURE=spec/fixtures/python_version_invalid/
+        run: make run FIXTURE=spec/fixtures/python_version_file_invalid_version/ COMPILE_FAILURE_EXIT_CODE=0
diff --git a/.github/workflows/hatchet_app_cleaner.yml b/.github/workflows/hatchet_app_cleaner.yml
index b9eb06cdf..05343fb8a 100644
--- a/.github/workflows/hatchet_app_cleaner.yml
+++ b/.github/workflows/hatchet_app_cleaner.yml
@@ -19,12 +19,12 @@ jobs:
       HEROKU_DISABLE_AUTOUPDATE: 1
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v7
       - name: Install Ruby and dependencies
         uses: ruby/setup-ruby@v1
         with:
           bundler-cache: true
-          ruby-version: "3.3"
+          ruby-version: "4.0"
       - name: Run Hatchet destroy
         # Only apps older than 10 minutes are destroyed, to ensure that any
         # in progress CI runs are not interrupted.
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
new file mode 100644
index 000000000..16872d5c9
--- /dev/null
+++ b/.github/workflows/release.yml
@@ -0,0 +1,36 @@
+name: Release Buildpack
+
+on:
+  # Auto-trigger when the "Prepare release" PR (created by the
+  # _classic-buildpack-prepare-release.yml workflow) is merged.
+  pull_request:
+    branches:
+      - main
+    types:
+      - closed
+  workflow_dispatch:
+
+permissions:
+  id-token: write
+  contents: write
+
+jobs:
+  release:
+    name: Release
+    # On `pull_request`, only run for the merged auto-generated
+    # "Prepare release" PR (branch name set by
+    # _classic-buildpack-prepare-release.yml). Manual dispatches always run.
+    if: >-
+      github.event_name == 'workflow_dispatch' ||
+      (github.event.pull_request.merged == true &&
+       github.event.pull_request.head.repo.full_name == github.repository &&
+       github.event.pull_request.head.ref == 'prepare-release' &&
+       github.event.pull_request.user.login == 'heroku-linguist[bot]')
+    uses: heroku/languages-github-actions/.github/workflows/_classic-buildpack-publish.yml@latest
+    with:
+      buildpack_id: "heroku/python"
+      app_id: ${{ vars.LINGUIST_GH_APP_ID }}
+    secrets:
+      app_private_key: ${{ secrets.LINGUIST_GH_PRIVATE_KEY }}
+      slack_webhook_url: ${{ secrets.BUILDPACK_RELEASE_FAILURE_WEBHOOK_URL }}
+      honeycomb_api_key: ${{ secrets.HONEYCOMB_API_KEY }}
diff --git a/.gitignore b/.gitignore
index e415b62c2..4cecc5fe2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,4 @@
 __pycache__/
-.hatchet/repos/
 .venv/
 # The setup-ruby GitHub Action creates this directory when caching is enabled, so we ignore
 # it here so it does not show up in the output of `git ls-files` for `make lint-scripts`.
diff --git a/.rubocop.yml b/.rubocop.yml
index 44a322aef..2edf1e039 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -1,4 +1,4 @@
-require:
+plugins:
   - rubocop-rspec
 
 AllCops:
diff --git a/.shellcheckrc b/.shellcheckrc
index 44e54caa5..da9f6a163 100644
--- a/.shellcheckrc
+++ b/.shellcheckrc
@@ -1,15 +1,2 @@
 # Enable all checks, including the optional ones that are off by default.
 enable=all
-
-# TODO: Triage and potentially enable more of these optional checks.
-
-# SC2154 (warning): var is referenced but not assigned.
-disable=SC2154
-# SC2250 (style): Prefer putting braces around variable references even when not strictly required.
-disable=SC2250
-# SC2310 (info): This function is invoked in an 'if' condition so set -e will be disabled.
-disable=SC2310
-# SC2311 (info): Bash implicitly disabled set -e for this function invocation because it's inside a command substitution.
-disable=SC2311
-# SC2312 (info): Consider invoking this command separately to avoid masking its return value
-disable=SC2312
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 23f823115..3648b20a2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,533 @@
 ## [Unreleased]
 
 
+## [v347] - 2026-07-10
+
+- Updated Pipenv from 2026.6.1 to 2026.6.2. ([#2111](https://github.com/heroku/heroku-buildpack-python/pull/2111))
+- Updated uv from 0.11.19 to 0.11.28. ([#2111](https://github.com/heroku/heroku-buildpack-python/pull/2111))
+
+## [v346] - 2026-06-10
+
+- The Python 3.14 version alias now resolves to Python 3.14.6. ([#2105](https://github.com/heroku/heroku-buildpack-python/pull/2105))
+- The Python 3.13 version alias now resolves to Python 3.13.14. ([#2105](https://github.com/heroku/heroku-buildpack-python/pull/2105))
+
+## [v345] - 2026-06-04
+
+- Updated pip from 26.1.1 to 26.1.2. ([#2098](https://github.com/heroku/heroku-buildpack-python/pull/2098))
+- Updated Poetry from 2.4.0 to 2.4.1. ([#2098](https://github.com/heroku/heroku-buildpack-python/pull/2098))
+- Updated uv from 0.11.11 to 0.11.19. ([#2098](https://github.com/heroku/heroku-buildpack-python/pull/2098))
+- The Python 3.14 version alias now resolves to Python 3.14.5. ([#2094](https://github.com/heroku/heroku-buildpack-python/pull/2094))
+
+## [v344] - 2026-05-07
+
+- Updated pip from 26.0.1 to 26.1.1. ([#2089](https://github.com/heroku/heroku-buildpack-python/pull/2089))
+- Updated Pipenv from 2026.5.2 to 2026.6.1. ([#2082](https://github.com/heroku/heroku-buildpack-python/pull/2082))
+- Updated Poetry from 2.3.4 to 2.4.0. ([#2088](https://github.com/heroku/heroku-buildpack-python/pull/2088))
+- Updated uv from 0.11.6 to 0.11.11. ([#2090](https://github.com/heroku/heroku-buildpack-python/pull/2090))
+
+## [v343] - 2026-04-13
+
+- Updated Pipenv from 2026.5.1 to 2026.5.2. ([#2080](https://github.com/heroku/heroku-buildpack-python/pull/2080))
+- Updated Poetry from 2.3.3 to 2.3.4. ([#2079](https://github.com/heroku/heroku-buildpack-python/pull/2079))
+- Updated uv from 0.11.3 to 0.11.6. ([#2078](https://github.com/heroku/heroku-buildpack-python/pull/2078))
+
+## [v342] - 2026-04-09
+
+- Added support for Heroku-26. ([#2073](https://github.com/heroku/heroku-buildpack-python/pull/2073))
+
+## [v341] - 2026-04-07
+
+- The Python 3.14 version alias now resolves to Python 3.14.4. ([#2071](https://github.com/heroku/heroku-buildpack-python/pull/2071))
+- The Python 3.13 version alias now resolves to Python 3.13.13. ([#2071](https://github.com/heroku/heroku-buildpack-python/pull/2071))
+
+## [v340] - 2026-04-02
+
+- Updated Pipenv from 2026.0.3 to 2026.5.1. ([#2065](https://github.com/heroku/heroku-buildpack-python/pull/2065))
+- Updated Poetry from 2.3.2 to 2.3.3. ([#2064](https://github.com/heroku/heroku-buildpack-python/pull/2064))
+- Updated uv from 0.10.9 to 0.11.3. ([#2067](https://github.com/heroku/heroku-buildpack-python/pull/2067))
+
+## [v339] - 2026-03-13
+
+- Updated uv from 0.10.7 to 0.10.9. ([#2049](https://github.com/heroku/heroku-buildpack-python/pull/2049))
+- Switched to downloading uv from `releases.astral.sh` instead of GitHub releases. ([#2050](https://github.com/heroku/heroku-buildpack-python/pull/2050))
+- Updated the check for misspelled `.python-version` files with additional misspellings seen in the wild. ([#2051](https://github.com/heroku/heroku-buildpack-python/pull/2051))
+
+## [v338] - 2026-03-03
+
+- The Python 3.12 version alias now resolves to Python 3.12.13. ([#2046](https://github.com/heroku/heroku-buildpack-python/pull/2046))
+- The Python 3.11 version alias now resolves to Python 3.11.15. ([#2046](https://github.com/heroku/heroku-buildpack-python/pull/2046))
+- The Python 3.10 version alias now resolves to Python 3.10.20. ([#2046](https://github.com/heroku/heroku-buildpack-python/pull/2046))
+
+## [v337] - 2026-03-03
+
+- Updated pip from 25.3 to 26.0.1. ([#2032](https://github.com/heroku/heroku-buildpack-python/pull/2032))
+- Updated uv from 0.10.1 to 0.10.7. ([#2041](https://github.com/heroku/heroku-buildpack-python/pull/2041))
+- Explicitly configured uv to use hard links to maintain the behaviour of previous versions. ([#2044](https://github.com/heroku/heroku-buildpack-python/pull/2044))
+
+## [v336] - 2026-03-02
+
+- Added a workaround for `nltk.txt` package downloader errors caused by an upstream regression in NLTK v3.9.3. ([#2041](https://github.com/heroku/heroku-buildpack-python/pull/2041))
+- Changed the S3 URL used to download Python to use AWS' dual-stack (IPv6 compatible) endpoint. ([#2035](https://github.com/heroku/heroku-buildpack-python/pull/2035))
+
+## [v335] - 2026-02-10
+
+- Updated uv from 0.9.29 to 0.10.1. ([#2031](https://github.com/heroku/heroku-buildpack-python/pull/2031))
+
+## [v334] - 2026-02-04
+
+- Updated Poetry from 2.3.1 to 2.3.2. ([#2024](https://github.com/heroku/heroku-buildpack-python/pull/2024))
+- Updated uv from 0.9.26 to 0.9.29. ([#2029](https://github.com/heroku/heroku-buildpack-python/pull/2029))
+
+## [v333] - 2026-02-04
+
+- The Python 3.14 version alias now resolves to Python 3.14.3. ([#2027](https://github.com/heroku/heroku-buildpack-python/pull/2027))
+- The Python 3.13 version alias now resolves to Python 3.13.12. ([#2027](https://github.com/heroku/heroku-buildpack-python/pull/2027))
+
+## [v332] - 2026-01-26
+
+- Updated Poetry from 2.2.1 to 2.3.1. ([#2019](https://github.com/heroku/heroku-buildpack-python/pull/2019))
+- Updated uv from 0.9.24 to 0.9.26. ([#2016](https://github.com/heroku/heroku-buildpack-python/pull/2016))
+- The web server concurrency calculation profile script now sets the env var `WEB_CONCURRENCY_SET_BY="heroku/python"` if `WEB_CONCURRENCY` was set automatically by the buildpack. ([#2015](https://github.com/heroku/heroku-buildpack-python/pull/2015))
+
+## [v331] - 2026-01-11
+
+- Updated uv from 0.9.21 to 0.9.24. ([#2013](https://github.com/heroku/heroku-buildpack-python/pull/2013))
+
+## [v330] - 2026-01-08
+
+- Re-apply a workaround for a Pipenv bug when using `--system`, that causes packages to not be installed correctly if they are also a dependency of Pipenv (such as `certifi` or `packaging`). ([#2011](https://github.com/heroku/heroku-buildpack-python/pull/2011))
+
+## [v329] - 2026-01-08
+
+- Updated Pipenv from 2025.0.4 to 2026.0.3. ([#2000](https://github.com/heroku/heroku-buildpack-python/pull/2000))
+
+## [v328] - 2026-01-07
+
+- Updated pip from 25.2 to 25.3. ([#2008](https://github.com/heroku/heroku-buildpack-python/pull/2008))
+- Stopped installing wheel when using pip with Python 3.12 and older. ([#2008](https://github.com/heroku/heroku-buildpack-python/pull/2008))
+
+## [v327] - 2026-01-07
+
+- Removed support for Python 3.9. ([#2005](https://github.com/heroku/heroku-buildpack-python/pull/2005))
+- Adjusted the error message shown if SQLite headers aren't found during package installation. ([#2006](https://github.com/heroku/heroku-buildpack-python/pull/2006))
+
+## [v326] - 2026-01-05
+
+- Updated uv from 0.9.17 to 0.9.21. ([#2003](https://github.com/heroku/heroku-buildpack-python/pull/2003))
+
+## [v325] - 2025-12-10
+
+- The build now errors if the files for multiple package managers are found. This replaces the warning displayed since November 2024. ([#1993](https://github.com/heroku/heroku-buildpack-python/pull/1993))
+- Sunset the previously deprecated support for falling back to installing dependencies from a `setup.py` file if no Python package manager files were found. ([#1992](https://github.com/heroku/heroku-buildpack-python/pull/1992))
+- Updated uv from 0.9.14 to 0.9.17. ([#1995](https://github.com/heroku/heroku-buildpack-python/pull/1995))
+
+## [v324] - 2025-12-09
+
+- The build now errors if an existing Python virtual environment is found in the build directory at `.venv/` or `venv/`. This replaces the warning displayed since September 2025. ([#1990](https://github.com/heroku/heroku-buildpack-python/pull/1990))
+- Stopped adding the current working directory to `PATH`. ([#1987](https://github.com/heroku/heroku-buildpack-python/pull/1987))
+
+## [v323] - 2025-12-05
+
+- Changed the default Python version for new apps from 3.13 to 3.14. ([#1984](https://github.com/heroku/heroku-buildpack-python/pull/1984))
+- The Python 3.14 version alias now resolves to Python 3.14.2. ([#1985](https://github.com/heroku/heroku-buildpack-python/pull/1985))
+- The Python 3.13 version alias now resolves to Python 3.13.11. ([#1985](https://github.com/heroku/heroku-buildpack-python/pull/1985))
+
+## [v322] - 2025-12-02
+
+- The Python 3.14 version alias now resolves to Python 3.14.1. ([#1982](https://github.com/heroku/heroku-buildpack-python/pull/1982))
+- The Python 3.13 version alias now resolves to Python 3.13.10. ([#1982](https://github.com/heroku/heroku-buildpack-python/pull/1982))
+- Updated uv from 0.9.11 to 0.9.14. ([#1979](https://github.com/heroku/heroku-buildpack-python/pull/1979))
+
+## [v321] - 2025-11-21
+
+- Deprecated support for Python 3.10. ([#1972](https://github.com/heroku/heroku-buildpack-python/pull/1972))
+- Updated uv from 0.9.9 to 0.9.11. ([#1973](https://github.com/heroku/heroku-buildpack-python/pull/1973))
+- Added more messaging to the build log recommending uv. ([#1975](https://github.com/heroku/heroku-buildpack-python/pull/1975))
+- Switched from using `--disable-pip-version-check` to the env var `PIP_DISABLE_PIP_VERSION_CHECK=1` when using pip. ([#1974](https://github.com/heroku/heroku-buildpack-python/pull/1974))
+
+## [v320] - 2025-11-20
+
+- Added a check for misspelled `.python-version` files. ([#1970](https://github.com/heroku/heroku-buildpack-python/pull/1970))
+- Fixed regex for null bytes character replacement to replace all occurrences, not just the first. ([#1966](https://github.com/heroku/heroku-buildpack-python/pull/1966))
+- Unpinned Poetry's `dulwich` version, since the upstream incompatibility with older Python has been fixed. ([#1967](https://github.com/heroku/heroku-buildpack-python/pull/1967))
+
+## [v319] - 2025-11-14
+
+- Updated uv from 0.9.7 to 0.9.9. ([#1961](https://github.com/heroku/heroku-buildpack-python/pull/1961))
+- Improved the error message shown for `.python-version` files that contain unexpected ASCII control code characters. ([#1962](https://github.com/heroku/heroku-buildpack-python/pull/1962))
+- Fixed Bash command substitution warnings from being shown if `runtime.txt` contains null byte characters. ([#1962](https://github.com/heroku/heroku-buildpack-python/pull/1962))
+- Improved the error message shown if the buildpack's build data file is deleted by a pre/post-compile hook. ([#1963](https://github.com/heroku/heroku-buildpack-python/pull/1963))
+
+## [v318] - 2025-11-12
+
+- Improved the error message shown when a `.python-version` file uses an unsupported file encoding. ([#1958](https://github.com/heroku/heroku-buildpack-python/pull/1958))
+- Improved the error message shown when a `.python-version` or `runtime.txt` file contains an invalid Python version. ([#1958](https://github.com/heroku/heroku-buildpack-python/pull/1958))
+- Added support for commented lines in `runtime.txt`, for parity with `.python-version`. ([#1958](https://github.com/heroku/heroku-buildpack-python/pull/1958))
+
+## [v317] - 2025-11-03
+
+- The Python 3.9 version alias now resolves to Python 3.9.25. ([#1955](https://github.com/heroku/heroku-buildpack-python/pull/1955))
+- Updated uv from 0.9.5 to 0.9.7. ([#1952](https://github.com/heroku/heroku-buildpack-python/pull/1952))
+
+## [v316] - 2025-10-27
+
+- Improved the error message when a `.python-version` or `runtime.txt` file contains invisible Unicode whitespace characters. ([#1947](https://github.com/heroku/heroku-buildpack-python/pull/1947))
+- Added metrics for the file encoding of `.python-version` and `runtime.txt` files. ([#1948](https://github.com/heroku/heroku-buildpack-python/pull/1948))
+
+## [v315] - 2025-10-22
+
+- Updated uv from 0.8.23 to 0.9.5. ([#1942](https://github.com/heroku/heroku-buildpack-python/pull/1942) and [#1945](https://github.com/heroku/heroku-buildpack-python/pull/1945))
+- Pinned `dulwich` version when using Poetry to work around an incompatibility with Python <3.9.2. ([#1943](https://github.com/heroku/heroku-buildpack-python/pull/1943))
+- Removed redundant internal error handling for venv creation. ([#1937](https://github.com/heroku/heroku-buildpack-python/pull/1937))
+
+## [v314] - 2025-10-15
+
+- The Python 3.13 version alias now resolves to Python 3.13.9. ([#1934](https://github.com/heroku/heroku-buildpack-python/pull/1934))
+- Improved error messages and metrics for unhandled buildpack errors. ([#1933](https://github.com/heroku/heroku-buildpack-python/pull/1933))
+
+## [v313] - 2025-10-09
+
+- Added support for Python 3.14. ([#1927](https://github.com/heroku/heroku-buildpack-python/pull/1927))
+- The Python 3.13 version alias now resolves to Python 3.13.8. ([#1928](https://github.com/heroku/heroku-buildpack-python/pull/1928))
+- The Python 3.12 version alias now resolves to Python 3.12.12. ([#1929](https://github.com/heroku/heroku-buildpack-python/pull/1929))
+- The Python 3.11 version alias now resolves to Python 3.11.14. ([#1929](https://github.com/heroku/heroku-buildpack-python/pull/1929))
+- The Python 3.10 version alias now resolves to Python 3.10.19. ([#1929](https://github.com/heroku/heroku-buildpack-python/pull/1929))
+- The Python 3.9 version alias now resolves to Python 3.9.24. ([#1929](https://github.com/heroku/heroku-buildpack-python/pull/1929))
+- Stopped using `--with-system-expat` when compiling new Python versions. ([#1925](https://github.com/heroku/heroku-buildpack-python/pull/1925))
+
+## [v312] - 2025-10-05
+
+- Updated uv from 0.8.20 to 0.8.23. ([#1916](https://github.com/heroku/heroku-buildpack-python/pull/1916) and [#1922](https://github.com/heroku/heroku-buildpack-python/pull/1922))
+
+## [v311] - 2025-09-30
+
+- Stopped rewriting Django collectstatic command log output. ([#1918](https://github.com/heroku/heroku-buildpack-python/pull/1918))
+- Changed the `pip install` command used to install the pip, Pipenv and Poetry package managers to now use `--isolated` mode. ([#1915](https://github.com/heroku/heroku-buildpack-python/pull/1915))
+- Added more Python project related file and directory names to the list recognised by buildpack detection. ([#1914](https://github.com/heroku/heroku-buildpack-python/pull/1914))
+
+## [v310] - 2025-09-23
+
+- Updated Poetry from 2.2.0 to 2.2.1. ([#1907](https://github.com/heroku/heroku-buildpack-python/pull/1907))
+- Updated uv from 0.8.18 to 0.8.20. ([#1910](https://github.com/heroku/heroku-buildpack-python/pull/1910))
+- Fixed errors saving the build cache when installed packages contain broken symlinks. ([#1909](https://github.com/heroku/heroku-buildpack-python/pull/1909))
+- Improved metrics for failed uv archive downloads. ([#1908](https://github.com/heroku/heroku-buildpack-python/pull/1908))
+
+## [v309] - 2025-09-19
+
+- Added metrics for misspelled `.python-version` files. ([#1904](https://github.com/heroku/heroku-buildpack-python/pull/1904))
+
+## [v308] - 2025-09-19
+
+- Updated Poetry from 2.1.4 to 2.2.0. ([#1900](https://github.com/heroku/heroku-buildpack-python/pull/1900))
+- Updated uv from 0.8.15 to 0.8.18. ([#1899](https://github.com/heroku/heroku-buildpack-python/pull/1899) and [#1901](https://github.com/heroku/heroku-buildpack-python/pull/1901))
+- Improved performance of Python build cache saving. ([#1902](https://github.com/heroku/heroku-buildpack-python/pull/1902))
+
+## [v307] - 2025-09-10
+
+- Deprecated support for falling back to installing dependencies from a `setup.py` file if no Python package manager files were found. ([#1897](https://github.com/heroku/heroku-buildpack-python/pull/1897))
+
+## [v306] - 2025-09-09
+
+- Updated uv from 0.8.13 to 0.8.15. ([#1894](https://github.com/heroku/heroku-buildpack-python/pull/1894))
+
+## [v305] - 2025-09-02
+
+- Added a warning if an existing Python virtual environment is found in the build directory at `.venv/` or `venv/`. In the future this warning will be made an error. ([#1890](https://github.com/heroku/heroku-buildpack-python/pull/1890))
+
+## [v304] - 2025-09-01
+
+- Fixed Django collectstatic and NLTK downloader support for apps that use config vars that shadow internal buildpack variable names (such as `CACHE_DIR`). ([#1888](https://github.com/heroku/heroku-buildpack-python/pull/1888))
+
+## [v303] - 2025-08-26
+
+- Updated uv from 0.8.9 to 0.8.13. ([#1880](https://github.com/heroku/heroku-buildpack-python/pull/1880))
+- Reduced default curl timeouts for faster retries of any transient connection issues on Heroku. ([#1884](https://github.com/heroku/heroku-buildpack-python/pull/1884))
+- Added support for overriding the default curl timeouts using `CURL_CONNECT_TIMEOUT` and `CURL_TIMEOUT`. These are intended for use in non-Heroku environments with slow connections, and so must be set via the build system rather than app config vars. ([#1884](https://github.com/heroku/heroku-buildpack-python/pull/1884))
+- Improved log output during curl retry attempts. ([#1884](https://github.com/heroku/heroku-buildpack-python/pull/1884))
+- Switched to Bash 5.0's `EPOCHREALTIME` for buildpack data store timing logic. ([#1881](https://github.com/heroku/heroku-buildpack-python/pull/1881))
+
+## [v302] - 2025-08-21
+
+- Stopped setting the `PYTHONHASHSEED` env var. ([#1876](https://github.com/heroku/heroku-buildpack-python/pull/1876))
+- Removed support for `BUILDPACK_S3_BASE_URL`. ([#1875](https://github.com/heroku/heroku-buildpack-python/pull/1875))
+- Refactored buildpack data store and `bin/report` to simplify the implementation and fix some string escaping bugs. ([#1878](https://github.com/heroku/heroku-buildpack-python/pull/1878))
+
+## [v301] - 2025-08-18
+
+- Simplified the handling of caches written by older buildpack versions. ([#1870](https://github.com/heroku/heroku-buildpack-python/pull/1870))
+
+## [v300] - 2025-08-15
+
+- The Python 3.13 version alias now resolves to Python 3.13.7. ([#1868](https://github.com/heroku/heroku-buildpack-python/pull/1868))
+
+## [v299] - 2025-08-13
+
+- Updated uv from 0.8.5 to 0.8.9. ([#1866](https://github.com/heroku/heroku-buildpack-python/pull/1866))
+
+## [v298] - 2025-08-06
+
+- The Python 3.13 version alias now resolves to Python 3.13.6. ([#1861](https://github.com/heroku/heroku-buildpack-python/pull/1861))
+- Fixed the stack version check to correctly show the "stack not supported" error message for the EOL Heroku-20, instead of "stack not recognised". ([#1860](https://github.com/heroku/heroku-buildpack-python/pull/1860))
+
+## [v297] - 2025-08-06
+
+- Updated pip from 25.1.1 to 25.2. ([#1848](https://github.com/heroku/heroku-buildpack-python/pull/1848))
+- Updated Poetry from 2.1.3 to 2.1.4. ([#1858](https://github.com/heroku/heroku-buildpack-python/pull/1858))
+- Updated uv from 0.8.4 to 0.8.5. ([#1857](https://github.com/heroku/heroku-buildpack-python/pull/1857))
+
+## [v296] - 2025-08-06
+
+- Stopped installing SQLite headers and CLI. ([#1854](https://github.com/heroku/heroku-buildpack-python/pull/1854))
+
+## [v295] - 2025-08-01
+
+- Updated uv from 0.7.20 to 0.8.4. ([#1847](https://github.com/heroku/heroku-buildpack-python/pull/1847))
+- Reduced the verbosity of pip's `Requirement already satisfied:` log lines when using Python 3.10 and older. ([#1851](https://github.com/heroku/heroku-buildpack-python/pull/1851))
+
+## [v294] - 2025-07-28
+
+- Improved performance of Python build cache restoration. ([#1845](https://github.com/heroku/heroku-buildpack-python/pull/1845))
+- Added a build log message for the build cache saving step. ([#1844](https://github.com/heroku/heroku-buildpack-python/pull/1844))
+
+## [v293] - 2025-07-23
+
+- Work around a Pipenv bug when using `--system`, that causes packages to not be installed correctly if they are also a dependency of Pipenv (such as `certifi`). ([#1842](https://github.com/heroku/heroku-buildpack-python/pull/1842))
+
+## [v292] - 2025-07-23
+
+- Updated Pipenv from 2024.0.1 to 2025.0.4. ([#1840](https://github.com/heroku/heroku-buildpack-python/pull/1840))
+- Fixed the way Pipenv is installed, so that it and its dependencies are installed into a separate virtual environment rather than the same environment as the app. If your app inadvertently depended on Pipenv's internal dependencies, you will need to add those dependencies explicitly to your `Pipfile`. ([#1840](https://github.com/heroku/heroku-buildpack-python/pull/1840))
+- Stopped installing pip when Pipenv is the chosen package manager. ([#1840](https://github.com/heroku/heroku-buildpack-python/pull/1840))
+- The build cache is now cleared when using Pipenv if the contents of `Pipfile.lock` has changed since the last build. This is required to work around Pipenv not uninstalling packages when they are removed from the lockfile. ([#1840](https://github.com/heroku/heroku-buildpack-python/pull/1840))
+- The build now errors when using Pipenv without its lockfile (`Pipfile.lock`). This replaces the warning displayed since November 2024. ([#1833](https://github.com/heroku/heroku-buildpack-python/pull/1833))
+
+## [v291] - 2025-07-10
+
+- Updated uv from 0.7.13 to 0.7.20. ([#1827](https://github.com/heroku/heroku-buildpack-python/pull/1827) and [#1829](https://github.com/heroku/heroku-buildpack-python/pull/1829))
+- The build now errors if the Python buildpack has been run multiple times in the same build. This replaces the warning displayed since December 2024. ([#1830](https://github.com/heroku/heroku-buildpack-python/pull/1830))
+- The build now errors if an existing `.heroku/python/` directory is found in the app source. This replaces the warning displayed since December 2024. ([#1830](https://github.com/heroku/heroku-buildpack-python/pull/1830))
+
+## [v290] - 2025-06-17
+
+- Updated uv from 0.7.10 to 0.7.13. ([#1819](https://github.com/heroku/heroku-buildpack-python/pull/1819))
+
+## [v289] - 2025-06-12
+
+- The Python 3.13 version alias now resolves to Python 3.13.5. ([#1814](https://github.com/heroku/heroku-buildpack-python/pull/1814))
+
+## [v288] - 2025-06-03
+
+- The Python 3.13 version alias now resolves to Python 3.13.4. ([#1810](https://github.com/heroku/heroku-buildpack-python/pull/1810))
+- The Python 3.12 version alias now resolves to Python 3.12.11. ([#1810](https://github.com/heroku/heroku-buildpack-python/pull/1810))
+- The Python 3.11 version alias now resolves to Python 3.11.13. ([#1810](https://github.com/heroku/heroku-buildpack-python/pull/1810))
+- The Python 3.10 version alias now resolves to Python 3.10.18. ([#1810](https://github.com/heroku/heroku-buildpack-python/pull/1810))
+- The Python 3.9 version alias now resolves to Python 3.9.23. ([#1810](https://github.com/heroku/heroku-buildpack-python/pull/1810))
+- Updated uv from 0.7.6 to 0.7.10. ([#1811](https://github.com/heroku/heroku-buildpack-python/pull/1811))
+
+## [v287] - 2025-05-20
+
+- Updated pip from 25.0.1 to 25.1.1. ([#1795](https://github.com/heroku/heroku-buildpack-python/pull/1795))
+- Updated Poetry from 2.1.2 to 2.1.3. ([#1797](https://github.com/heroku/heroku-buildpack-python/pull/1797))
+- Updated uv from 0.7.3 to 0.7.6. ([#1800](https://github.com/heroku/heroku-buildpack-python/pull/1800) and [#1803](https://github.com/heroku/heroku-buildpack-python/pull/1803))
+
+## [v286] - 2025-05-13
+
+- Added support for the package manager uv. ([#1791](https://github.com/heroku/heroku-buildpack-python/pull/1791))
+
+## [v285] - 2025-05-08
+
+- Improved internal buildpack metrics handling of attributes that contain newline characters. ([#1792](https://github.com/heroku/heroku-buildpack-python/pull/1792))
+
+## [v284] - 2025-05-06
+
+- Fixed parsing of `runtime.txt` and `.python-version` files that contain CRLF characters. ([#1789](https://github.com/heroku/heroku-buildpack-python/pull/1789))
+
+## [v283] - 2025-05-06
+
+- Added a warning when an app doesn't specify a Python version and instead relies upon the default/cached version. ([#1787](https://github.com/heroku/heroku-buildpack-python/pull/1787))
+- Improved the instructions for migrating from `runtime.txt` to `.python-version`. ([#1783](https://github.com/heroku/heroku-buildpack-python/pull/1783))
+- Improved the error messages shown when `.python-version`, `runtime.txt` or `Pipfile.lock` contain an invalid Python version. ([#1783](https://github.com/heroku/heroku-buildpack-python/pull/1783) and [#1786](https://github.com/heroku/heroku-buildpack-python/pull/1786))
+- Improved the rendering of the error message shown when `.python-version` or `runtime.txt` contain stray invisible characters (such as ASCII control codes). ([#1783](https://github.com/heroku/heroku-buildpack-python/pull/1783))
+- Improved the upgrade instructions shown for EOL and unsupported Python versions. ([#1783](https://github.com/heroku/heroku-buildpack-python/pull/1783) and [#1786](https://github.com/heroku/heroku-buildpack-python/pull/1786))
+- Improved the error messages shown when no Python package manager files are found. ([#1787](https://github.com/heroku/heroku-buildpack-python/pull/1787))
+
+## [v282] - 2025-05-02
+
+- Removed support for Heroku-20. ([#1778](https://github.com/heroku/heroku-buildpack-python/pull/1778))
+
+## [v281] - 2025-04-08
+
+- The Python 3.13 version alias now resolves to Python 3.13.3. ([#1775](https://github.com/heroku/heroku-buildpack-python/pull/1775))
+- The Python 3.12 version alias now resolves to Python 3.12.10. ([#1775](https://github.com/heroku/heroku-buildpack-python/pull/1775))
+- The Python 3.11 version alias now resolves to Python 3.11.12. ([#1775](https://github.com/heroku/heroku-buildpack-python/pull/1775))
+- The Python 3.10 version alias now resolves to Python 3.10.17. ([#1775](https://github.com/heroku/heroku-buildpack-python/pull/1775))
+- The Python 3.9 version alias now resolves to Python 3.9.22. ([#1775](https://github.com/heroku/heroku-buildpack-python/pull/1775))
+
+## [v280] - 2025-04-08
+
+- Updated pip from 24.3.1 to 25.0.1. ([#1759](https://github.com/heroku/heroku-buildpack-python/pull/1759))
+- Updated Poetry from 2.1.1 to 2.1.2. ([#1772](https://github.com/heroku/heroku-buildpack-python/pull/1772))
+
+## [v279] - 2025-02-26
+
+- Updated Poetry from 2.0.1 to 2.1.1. ([#1758](https://github.com/heroku/heroku-buildpack-python/pull/1758))
+- Stopped filtering out pip's `Requirement already satisfied:` log lines when installing dependencies. ([#1765](https://github.com/heroku/heroku-buildpack-python/pull/1765))
+- Improved the error messages shown if installing pip/Poetry/Pipenv fails. ([#1764](https://github.com/heroku/heroku-buildpack-python/pull/1764))
+- Stopped installing pip into Poetry's virtual environment. ([#1761](https://github.com/heroku/heroku-buildpack-python/pull/1761))
+
+## [v278] - 2025-02-24
+
+- Added build-time rewriting of editable VCS dependency paths (in addition to the existing run-time rewriting), to work around an upstream Pipenv bug with editable VCS dependencies not being reinstalled correctly for cached builds. ([#1756](https://github.com/heroku/heroku-buildpack-python/pull/1756))
+- Changed the location of repositories for editable VCS dependencies when using pip and Pipenv, to improve build performance and match the behaviour when using Poetry. ([#1753](https://github.com/heroku/heroku-buildpack-python/pull/1753))
+
+## [v277] - 2025-02-17
+
+- Improved the warning message shown when the requested Python version is not the latest patch version. ([#1749](https://github.com/heroku/heroku-buildpack-python/pull/1749))
+- Improved the error message shown when the requested Python patch version isn't available. ([#1749](https://github.com/heroku/heroku-buildpack-python/pull/1749))
+- Improved the error message shown if there was a networking or server related error downloading Python. ([#1749](https://github.com/heroku/heroku-buildpack-python/pull/1749))
+- Adjusted the curl options used when downloading Python to set a maximum download time of 120s to prevent hanging builds in the case of network issues. ([#1749](https://github.com/heroku/heroku-buildpack-python/pull/1749))
+- Refactored the Python download step to avoid an unnecessary version check `HEAD` request to S3 prior to downloading Python or reusing a cached install. ([#1749](https://github.com/heroku/heroku-buildpack-python/pull/1749))
+- Updated the `runtime.txt` deprecation warning to include a link to the deprecation changelog post. ([#1747](https://github.com/heroku/heroku-buildpack-python/pull/1747))
+- Improved buildpack metrics for Python version selection. ([#1749](https://github.com/heroku/heroku-buildpack-python/pull/1749))
+- Improved buildpack metrics for builds that fail. ([#1746](https://github.com/heroku/heroku-buildpack-python/pull/1746) and [#1749](https://github.com/heroku/heroku-buildpack-python/pull/1749))
+
+## [v276] - 2025-02-05
+
+- The Python 3.13 version alias now resolves to Python 3.13.2. ([#1744](https://github.com/heroku/heroku-buildpack-python/pull/1744))
+- The Python 3.12 version alias now resolves to Python 3.12.9. ([#1744](https://github.com/heroku/heroku-buildpack-python/pull/1744))
+- Deprecated support for the `runtime.txt` file. ([#1743](https://github.com/heroku/heroku-buildpack-python/pull/1743))
+- Improved the error messages shown when `.python-version`, `runtime.txt` or `Pipfile.lock` contain an invalid Python version. ([#1743](https://github.com/heroku/heroku-buildpack-python/pull/1743))
+
+## [v275] - 2025-01-13
+
+- Updated Poetry from 1.8.5 to 2.0.1. ([#1734](https://github.com/heroku/heroku-buildpack-python/pull/1734))
+
+## [v274] - 2025-01-08
+
+- Added a deprecation warning for Python 3.9. ([#1732](https://github.com/heroku/heroku-buildpack-python/pull/1732))
+- Removed support for Python 3.8. ([#1732](https://github.com/heroku/heroku-buildpack-python/pull/1732))
+- Improved the error messages shown for EOL or unrecognised major Python versions. ([#1732](https://github.com/heroku/heroku-buildpack-python/pull/1732))
+
+## [v273] - 2025-01-03
+
+- Added more Python project related file and directory names to the list recognised by buildpack detection. ([#1729](https://github.com/heroku/heroku-buildpack-python/pull/1729))
+- Improved the file listing in the error messages shown when buildpack detection fails or when no Python package manager files are found. ([#1728](https://github.com/heroku/heroku-buildpack-python/pull/1728))
+
+## [v272] - 2024-12-13
+
+- Added a warning if the Python buildpack has been run multiple times in the same build. In the future this warning will be made an error. ([#1724](https://github.com/heroku/heroku-buildpack-python/pull/1724))
+- Added a warning if an existing `.heroku/python/` directory is found in the app source. In the future this warning will be made an error. ([#1724](https://github.com/heroku/heroku-buildpack-python/pull/1724))
+- Improved the error message shown if the buildpack is used on an unsupported stack. ([#1724](https://github.com/heroku/heroku-buildpack-python/pull/1724))
+- Fixed Dev Center links to reflect recent article URL changes. ([#1723](https://github.com/heroku/heroku-buildpack-python/pull/1723))
+- Added metrics for the existence of a uv lockfile. ([#1725](https://github.com/heroku/heroku-buildpack-python/pull/1725))
+
+## [v271] - 2024-12-12
+
+- Updated the Python 3.8 EOL warning message with the new sunset date. ([#1721](https://github.com/heroku/heroku-buildpack-python/pull/1721))
+- Improved the error message shown when pip install fails due to pip rejecting a package with invalid version metadata. ([#1718](https://github.com/heroku/heroku-buildpack-python/pull/1718))
+- Improved the error message shown when the copy of pip bundled in the `ensurepip` module cannot be found. ([#1720](https://github.com/heroku/heroku-buildpack-python/pull/1720))
+
+## [v270] - 2024-12-10
+
+- Changed the default Python version for new apps from 3.12 to 3.13. ([#1715](https://github.com/heroku/heroku-buildpack-python/pull/1715))
+- Changed Python version pinning behaviour for apps that do not specify a Python version. Repeat builds are now pinned to the major Python version only (`3.X`) instead of the full Python version (`3.X.Y`), so that they always use the latest patch version. ([#1714](https://github.com/heroku/heroku-buildpack-python/pull/1714))
+- Updated Poetry from 1.8.4 to 1.8.5. ([#1716](https://github.com/heroku/heroku-buildpack-python/pull/1716))
+
+## [v269] - 2024-12-04
+
+- The Python 3.13 version alias now resolves to Python 3.13.1. ([#1712](https://github.com/heroku/heroku-buildpack-python/pull/1712))
+- The Python 3.12 version alias now resolves to Python 3.12.8. ([#1712](https://github.com/heroku/heroku-buildpack-python/pull/1712))
+- The Python 3.11 version alias now resolves to Python 3.11.11. ([#1712](https://github.com/heroku/heroku-buildpack-python/pull/1712))
+- The Python 3.10 version alias now resolves to Python 3.10.16. ([#1712](https://github.com/heroku/heroku-buildpack-python/pull/1712))
+- The Python 3.9 version alias now resolves to Python 3.9.21. ([#1712](https://github.com/heroku/heroku-buildpack-python/pull/1712))
+
+## [v268] - 2024-12-04
+
+- Updated pip from 24.0 to 24.3.1. ([#1685](https://github.com/heroku/heroku-buildpack-python/pull/1685))
+- Updated wheel from 0.44.0 to 0.45.1. ([#1707](https://github.com/heroku/heroku-buildpack-python/pull/1707))
+
+## [v267] - 2024-11-12
+
+- Deprecated using Pipenv without a lockfile (`Pipfile.lock`). ([#1695](https://github.com/heroku/heroku-buildpack-python/pull/1695))
+- Fixed Poetry venv creation when using an outdated Python version whose `ensurepip` module doesn't enable isolated mode, and the app's build directory contents shadows a package imported by pip (such as `brotli`). ([#1698](https://github.com/heroku/heroku-buildpack-python/pull/1698))
+
+## [v266] - 2024-11-08
+
+- Added a warning when the files for multiple package managers are found. In the future this warning will become an error. ([#1692](https://github.com/heroku/heroku-buildpack-python/pull/1692))
+- Updated the build log message shown when installing dependencies to include the package manager command being run. ([#1689](https://github.com/heroku/heroku-buildpack-python/pull/1689))
+- Changed test dependency installation on Heroku CI to now install `requirements.txt` and `requirements-test.txt` in a single `pip install` invocation rather than separately. This allows pip's resolver to resolve any version conflicts between the two files. ([#1689](https://github.com/heroku/heroku-buildpack-python/pull/1689))
+- Improved the error messages and buildpack metrics for package manager related failures. ([#1689](https://github.com/heroku/heroku-buildpack-python/pull/1689))
+- Improved the build log output, error messages and buildpack failure metrics for the NLTK downloader feature. ([#1690](https://github.com/heroku/heroku-buildpack-python/pull/1690))
+
+## [v265] - 2024-11-06
+
+- Fixed Poetry installation when using outdated patch versions of Python 3.8, 3.9 and 3.10, whose bundled pip doesn't support the `--python` option. ([#1687](https://github.com/heroku/heroku-buildpack-python/pull/1687))
+
+## [v264] - 2024-11-06
+
+- Added support for the package manager Poetry. Apps must have a `pyproject.toml` + `poetry.lock` and no other package manager files (otherwise pip/Pipenv will take precedence for backwards compatibility). ([#1682](https://github.com/heroku/heroku-buildpack-python/pull/1682))
+
+## [v263] - 2024-10-31
+
+- Fixed cache handling so that it now also discards the cache when the package manager (or its version) changes. ([#1679](https://github.com/heroku/heroku-buildpack-python/pull/1679))
+- Improved the build log output shown when restoring or discarding the cache. For example, if the cache was invalidated all reasons are now shown. ([#1679](https://github.com/heroku/heroku-buildpack-python/pull/1679))
+- Stopped performing unnecessary cache file copies when the cache is due to be invalidated. This required moving the cache restoration step to after the `bin/pre_compile` hook runs. ([#1679](https://github.com/heroku/heroku-buildpack-python/pull/1679))
+- Fixed cache restoration in the case where an app's `requirements.txt` was formerly a symlink. ([#1679](https://github.com/heroku/heroku-buildpack-python/pull/1679))
+- Added buildpack metrics for the status of the cache and duration of cache restoration/saving. ([#1679](https://github.com/heroku/heroku-buildpack-python/pull/1679))
+
+## [v262] - 2024-10-25
+
+- Updated buildpack-generated warning messages to use colour and be more consistently formatted. ([#1666](https://github.com/heroku/heroku-buildpack-python/pull/1666))
+- Improved build log output and error messages for the `bin/pre_compile` and `bin/post_compile` customisation hooks. ([#1667](https://github.com/heroku/heroku-buildpack-python/pull/1667))
+
+## [v261] - 2024-10-14
+
+- Added support for configuring the Python version using a `.python-version` file. Both the `3.N` and `3.N.N` version forms are supported (the former is recommended). The existing `runtime.txt` file will take precedence if both files are found, however, we recommend switching to `.python-version` since it is more commonly supported in the Python ecosystem. ([#1664](https://github.com/heroku/heroku-buildpack-python/pull/1664))
+- Added support for specifying only the Python major version in `runtime.txt` instead of requiring the full Python version (for example `python-3.N` instead of `python-3.N.N`). ([#1664](https://github.com/heroku/heroku-buildpack-python/pull/1664))
+
+## [v260] - 2024-10-10
+
+- Added support for Python 3.13. ([#1661](https://github.com/heroku/heroku-buildpack-python/pull/1661))
+- Removed the `idle3` and `pydoc3` scripts since they do not work with relocated Python and so have been broken for some time. Invoke them via their modules instead (e.g. `python -m pydoc`). ([#1661](https://github.com/heroku/heroku-buildpack-python/pull/1661))
+
+## [v259] - 2024-10-09
+
+- Improved build log output about the detected Python version. ([#1658](https://github.com/heroku/heroku-buildpack-python/pull/1658))
+- Improved error messages shown when the requested Python version is not a valid version string or is for an unknown/non-existent major Python version. ([#1658](https://github.com/heroku/heroku-buildpack-python/pull/1658))
+- Improved error messages shown when `Pipfile.lock` is not valid JSON. ([#1658](https://github.com/heroku/heroku-buildpack-python/pull/1658))
+- Fixed invalid Python versions being silently ignored when they were specified via the `python_version` field in `Pipfile.lock`. ([#1658](https://github.com/heroku/heroku-buildpack-python/pull/1658))
+- Added support for Python 3.9 on Heroku-24. ([#1656](https://github.com/heroku/heroku-buildpack-python/pull/1656))
+- Added buildpack metrics for use of outdated Python patch versions and occurrences of internal errors. ([#1657](https://github.com/heroku/heroku-buildpack-python/pull/1657))
+- Improved the robustness of buildpack error handling by enabling `inherit_errexit`. ([#1655](https://github.com/heroku/heroku-buildpack-python/pull/1655))
+
+## [v258] - 2024-10-01
+
+- Added support for Python 3.12.7. ([#1650](https://github.com/heroku/heroku-buildpack-python/pull/1650))
+- Changed the default Python version for new apps from 3.12.6 to 3.12.7. ([#1650](https://github.com/heroku/heroku-buildpack-python/pull/1650))
+- Fixed Django collectstatic debug output being shown if `DEBUG_COLLECTSTATIC` was set to `0` or the empty string. ([#1646](https://github.com/heroku/heroku-buildpack-python/pull/1646))
+- Stopped adding a trailing `:` to `C_INCLUDE_PATH`, `CPLUS_INCLUDE_PATH`, `LIBRARY_PATH`, `LD_LIBRARY_PATH` and `PKG_CONFIG_PATH`. ([#1645](https://github.com/heroku/heroku-buildpack-python/pull/1645))
+- Removed remnants of the unused `.heroku/vendor/` directory. ([#1644](https://github.com/heroku/heroku-buildpack-python/pull/1644))
+
+## [v257] - 2024-09-24
+
+- Moved the SQLite3 install step prior to installing dependencies when using Pipenv. This now matches the behaviour when using pip and allows dependencies to actually use the headers. ([#1640](https://github.com/heroku/heroku-buildpack-python/pull/1640))
+- Stopped exposing the `SKIP_PIP_INSTALL` env var to `bin/post_compile` and other subprocesses when using Pipenv. ([#1640](https://github.com/heroku/heroku-buildpack-python/pull/1640))
+- Stopped creating `.heroku/python/requirements-{declared,installed}.txt` files when using pip. ([#1640](https://github.com/heroku/heroku-buildpack-python/pull/1640))
+- Stopped creating a placeholder `requirements.txt` file when an app only has a `setup.py` file and no other package manager files. Instead pip is now invoked directly using `--editable .`. ([#1640](https://github.com/heroku/heroku-buildpack-python/pull/1640))
+- Improved buildpack metrics for package manager detection and duration of install steps. ([#1640](https://github.com/heroku/heroku-buildpack-python/pull/1640))
+- Updated buildpack-generated error messages to use colour and be more consistently formatted. ([#1639](https://github.com/heroku/heroku-buildpack-python/pull/1639))
+
+## [v256] - 2024-09-07
+
+- Added support for Python 3.8.20, 3.9.20, 3.10.15, 3.11.10 and 3.12.6. ([#1632](https://github.com/heroku/heroku-buildpack-python/pull/1632))
+- Changed the default Python version for new apps from 3.12.5 to 3.12.6. ([#1632](https://github.com/heroku/heroku-buildpack-python/pull/1632))
+- Updated wheel from 0.43.0 to 0.44.0. ([#1629](https://github.com/heroku/heroku-buildpack-python/pull/1629))
+
+## [v255] - 2024-08-07
+
+- Added support for Python 3.12.5. ([#1622](https://github.com/heroku/heroku-buildpack-python/pull/1622))
+- Changed the default Python version for new apps from 3.12.4 to 3.12.5. ([#1622](https://github.com/heroku/heroku-buildpack-python/pull/1622))
+
 ## [v254] - 2024-07-16
 
 - Updated setuptools from 69.2.0 to 70.3.0. ([#1614](https://github.com/heroku/heroku-buildpack-python/pull/1614))
@@ -67,7 +594,7 @@
 
 ## [v243] - 2024-02-07
 
-- Added support for Python 3.11.8 and 3.12.2. ([#1538](https://github.com/heroku/heroku-buildpack-python/pull/1538)).
+- Added support for Python 3.11.8 and 3.12.2. ([#1538](https://github.com/heroku/heroku-buildpack-python/pull/1538))
 - Changed the default Python version for new apps from 3.12.1 to 3.12.2. ([#1538](https://github.com/heroku/heroku-buildpack-python/pull/1538))
 
 ## [v242] - 2024-01-11
@@ -78,8 +605,8 @@
 
 ## [v241] - 2023-12-08
 
-- Changed the default Python version for new apps from Python 3.11 to Python 3.12. ([#1516](https://github.com/heroku/heroku-buildpack-python/pull/1516)).
-- Added support for Python 3.11.7 and 3.12.1. ([#1517](https://github.com/heroku/heroku-buildpack-python/pull/1517) and [#1518](https://github.com/heroku/heroku-buildpack-python/pull/1518)).
+- Changed the default Python version for new apps from Python 3.11 to Python 3.12. ([#1516](https://github.com/heroku/heroku-buildpack-python/pull/1516))
+- Added support for Python 3.11.7 and 3.12.1. ([#1517](https://github.com/heroku/heroku-buildpack-python/pull/1517) and [#1518](https://github.com/heroku/heroku-buildpack-python/pull/1518))
 - Added a deprecation warning for Python 3.8. ([#1515](https://github.com/heroku/heroku-buildpack-python/pull/1515))
 
 ## [v240] - 2023-11-30
@@ -518,7 +1045,7 @@
 
 ## v164 - 2020-02-20
 
-- Update requirements.txt builds to use Pip 20.0.2
+- Update requirements.txt builds to use pip 20.0.2
 - Download get-pip.py to tmpdir instead of root dir
 
 ## v163 - 2019-12-23
@@ -647,7 +1174,7 @@ Default to 3.6.5, bugfixes.
 
 ## v133
 
-Fixes for Pip 10 release.
+Fixes for pip 10 release.
 
 ## v132
 
@@ -955,7 +1482,7 @@ Updated pip and Setuptools.
 
 Added warnings for lack of Procfile.
 
-## v72 - 2015-12-07
+## v73 - 2015-12-07
 
 Updated default Python to 2.7.11.
 
@@ -993,81 +1520,174 @@ Improved compatibility with multi and node.js buildpacks.
 
 ## v63 - 2015-10-08
 
-Updated Pip and Setuptools.
+Updated pip and Setuptools.
 
 - Setuptools updated to v18.3.2
-- Pip updated to v7.1.2
+- pip updated to v7.1.2
 
 ## v62 - 2015-08-07
 
-Updated Pip and Setuptools.
+Updated pip and Setuptools.
 
 - Setuptools updated to v18.1
-- Pip updated to v7.1.0
+- pip updated to v7.1.0
 
 ## v61 - 2015-06-30
 
-Updated Pip and Setuptools.
+Updated pip and Setuptools.
 
 - Setuptools updated to v18.0.1
-- Pip updated to v7.0.3
+- pip updated to v7.0.3
 
 ## v60 - 2015-05-27
 
-Default Python is now latest 2.7.10. Updated Pip and Distribute.
+Default Python is now latest 2.7.10. Updated pip and Distribute.
 
 - Default Python version is v2.7.10
 - Setuptools updated to v16.0
-- Pip updated to v7.0.1
-
-[unreleased]: https://github.com/heroku/heroku-buildpack-python/compare/v254...main
-[v254]: https://github.com/heroku/heroku-buildpack-python/compare/v253...v254
-[v253]: https://github.com/heroku/heroku-buildpack-python/compare/v252...v253
-[v252]: https://github.com/heroku/heroku-buildpack-python/compare/v251...v252
-[v251]: https://github.com/heroku/heroku-buildpack-python/compare/v250...v251
-[v250]: https://github.com/heroku/heroku-buildpack-python/compare/v249...v250
-[v249]: https://github.com/heroku/heroku-buildpack-python/compare/v248...v249
-[v248]: https://github.com/heroku/heroku-buildpack-python/compare/v247...v248
-[v247]: https://github.com/heroku/heroku-buildpack-python/compare/v246...v247
-[v246]: https://github.com/heroku/heroku-buildpack-python/compare/v245...v246
-[v245]: https://github.com/heroku/heroku-buildpack-python/compare/v244...v245
-[v244]: https://github.com/heroku/heroku-buildpack-python/compare/v243...v244
-[v243]: https://github.com/heroku/heroku-buildpack-python/compare/v242...v243
-[v242]: https://github.com/heroku/heroku-buildpack-python/compare/v241...v242
-[v241]: https://github.com/heroku/heroku-buildpack-python/compare/v240...v241
-[v240]: https://github.com/heroku/heroku-buildpack-python/compare/v239...v240
-[v239]: https://github.com/heroku/heroku-buildpack-python/compare/v238...v239
-[v238]: https://github.com/heroku/heroku-buildpack-python/compare/v237...v238
-[v237]: https://github.com/heroku/heroku-buildpack-python/compare/v236...v237
-[v236]: https://github.com/heroku/heroku-buildpack-python/compare/v235...v236
-[v235]: https://github.com/heroku/heroku-buildpack-python/compare/v234...v235
-[v234]: https://github.com/heroku/heroku-buildpack-python/compare/v233...v234
-[v233]: https://github.com/heroku/heroku-buildpack-python/compare/v232...v233
-[v232]: https://github.com/heroku/heroku-buildpack-python/compare/v231...v232
-[v231]: https://github.com/heroku/heroku-buildpack-python/compare/v230...v231
-[v230]: https://github.com/heroku/heroku-buildpack-python/compare/v229...v230
-[v229]: https://github.com/heroku/heroku-buildpack-python/compare/v228...v229
-[v228]: https://github.com/heroku/heroku-buildpack-python/compare/v227...v228
-[v227]: https://github.com/heroku/heroku-buildpack-python/compare/v226...v227
-[v226]: https://github.com/heroku/heroku-buildpack-python/compare/v225...v226
-[v225]: https://github.com/heroku/heroku-buildpack-python/compare/v224...v225
-[v224]: https://github.com/heroku/heroku-buildpack-python/compare/v223...v224
-[v223]: https://github.com/heroku/heroku-buildpack-python/compare/v222...v223
-[v222]: https://github.com/heroku/heroku-buildpack-python/compare/v221...v222
-[v221]: https://github.com/heroku/heroku-buildpack-python/compare/v220...v221
-[v220]: https://github.com/heroku/heroku-buildpack-python/compare/v219...v220
-[v219]: https://github.com/heroku/heroku-buildpack-python/compare/v218...v219
-[v218]: https://github.com/heroku/heroku-buildpack-python/compare/v217...v218
-[v217]: https://github.com/heroku/heroku-buildpack-python/compare/v216...v217
-[v216]: https://github.com/heroku/heroku-buildpack-python/compare/v215...v216
-[v215]: https://github.com/heroku/heroku-buildpack-python/compare/v214...v215
-[v214]: https://github.com/heroku/heroku-buildpack-python/compare/v213...v214
-[v213]: https://github.com/heroku/heroku-buildpack-python/compare/v212...v213
-[v212]: https://github.com/heroku/heroku-buildpack-python/compare/v211...v212
-[v211]: https://github.com/heroku/heroku-buildpack-python/compare/v210...v211
-[v210]: https://github.com/heroku/heroku-buildpack-python/compare/v209...v210
-[v209]: https://github.com/heroku/heroku-buildpack-python/compare/v208...v209
-[v208]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v207...v208
+- pip updated to v7.0.1
+
+[unreleased]: https://github.com/heroku/heroku-buildpack-python/compare/v347...main
+[v347]: https://github.com/heroku/heroku-buildpack-python/compare/v346...v347
+[v346]: https://github.com/heroku/heroku-buildpack-python/compare/v345...v346
+[v345]: https://github.com/heroku/heroku-buildpack-python/compare/v344...v345
+[v344]: https://github.com/heroku/heroku-buildpack-python/compare/v343...v344
+[v343]: https://github.com/heroku/heroku-buildpack-python/compare/v342...v343
+[v342]: https://github.com/heroku/heroku-buildpack-python/compare/v341...v342
+[v341]: https://github.com/heroku/heroku-buildpack-python/compare/v340...v341
+[v340]: https://github.com/heroku/heroku-buildpack-python/compare/v339...v340
+[v339]: https://github.com/heroku/heroku-buildpack-python/compare/v338...v339
+[v338]: https://github.com/heroku/heroku-buildpack-python/compare/v337...v338
+[v337]: https://github.com/heroku/heroku-buildpack-python/compare/v336...v337
+[v336]: https://github.com/heroku/heroku-buildpack-python/compare/v335...v336
+[v335]: https://github.com/heroku/heroku-buildpack-python/compare/v334...v335
+[v334]: https://github.com/heroku/heroku-buildpack-python/compare/v333...v334
+[v333]: https://github.com/heroku/heroku-buildpack-python/compare/v332...v333
+[v332]: https://github.com/heroku/heroku-buildpack-python/compare/v331...v332
+[v331]: https://github.com/heroku/heroku-buildpack-python/compare/v330...v331
+[v330]: https://github.com/heroku/heroku-buildpack-python/compare/v329...v330
+[v329]: https://github.com/heroku/heroku-buildpack-python/compare/v328...v329
+[v328]: https://github.com/heroku/heroku-buildpack-python/compare/v327...v328
+[v327]: https://github.com/heroku/heroku-buildpack-python/compare/v326...v327
+[v326]: https://github.com/heroku/heroku-buildpack-python/compare/v325...v326
+[v325]: https://github.com/heroku/heroku-buildpack-python/compare/v324...v325
+[v324]: https://github.com/heroku/heroku-buildpack-python/compare/v323...v324
+[v323]: https://github.com/heroku/heroku-buildpack-python/compare/v322...v323
+[v322]: https://github.com/heroku/heroku-buildpack-python/compare/v321...v322
+[v321]: https://github.com/heroku/heroku-buildpack-python/compare/v320...v321
+[v320]: https://github.com/heroku/heroku-buildpack-python/compare/v319...v320
+[v319]: https://github.com/heroku/heroku-buildpack-python/compare/v318...v319
+[v318]: https://github.com/heroku/heroku-buildpack-python/compare/v317...v318
+[v317]: https://github.com/heroku/heroku-buildpack-python/compare/v316...v317
+[v316]: https://github.com/heroku/heroku-buildpack-python/compare/v315...v316
+[v315]: https://github.com/heroku/heroku-buildpack-python/compare/v314...v315
+[v314]: https://github.com/heroku/heroku-buildpack-python/compare/v313...v314
+[v313]: https://github.com/heroku/heroku-buildpack-python/compare/v312...v313
+[v312]: https://github.com/heroku/heroku-buildpack-python/compare/v311...v312
+[v311]: https://github.com/heroku/heroku-buildpack-python/compare/v310...v311
+[v310]: https://github.com/heroku/heroku-buildpack-python/compare/v309...v310
+[v309]: https://github.com/heroku/heroku-buildpack-python/compare/v308...v309
+[v308]: https://github.com/heroku/heroku-buildpack-python/compare/v307...v308
+[v307]: https://github.com/heroku/heroku-buildpack-python/compare/v306...v307
+[v306]: https://github.com/heroku/heroku-buildpack-python/compare/v305...v306
+[v305]: https://github.com/heroku/heroku-buildpack-python/compare/v304...v305
+[v304]: https://github.com/heroku/heroku-buildpack-python/compare/v303...v304
+[v303]: https://github.com/heroku/heroku-buildpack-python/compare/v302...v303
+[v302]: https://github.com/heroku/heroku-buildpack-python/compare/v301...v302
+[v301]: https://github.com/heroku/heroku-buildpack-python/compare/v300...v301
+[v300]: https://github.com/heroku/heroku-buildpack-python/compare/v299...v300
+[v299]: https://github.com/heroku/heroku-buildpack-python/compare/v298...v299
+[v298]: https://github.com/heroku/heroku-buildpack-python/compare/v297...v298
+[v297]: https://github.com/heroku/heroku-buildpack-python/compare/v296...v297
+[v296]: https://github.com/heroku/heroku-buildpack-python/compare/v295...v296
+[v295]: https://github.com/heroku/heroku-buildpack-python/compare/v294...v295
+[v294]: https://github.com/heroku/heroku-buildpack-python/compare/v293...v294
+[v293]: https://github.com/heroku/heroku-buildpack-python/compare/v292...v293
+[v292]: https://github.com/heroku/heroku-buildpack-python/compare/v291...v292
+[v291]: https://github.com/heroku/heroku-buildpack-python/compare/v290...v291
+[v290]: https://github.com/heroku/heroku-buildpack-python/compare/v289...v290
+[v289]: https://github.com/heroku/heroku-buildpack-python/compare/v288...v289
+[v288]: https://github.com/heroku/heroku-buildpack-python/compare/v287...v288
+[v287]: https://github.com/heroku/heroku-buildpack-python/compare/v286...v287
+[v286]: https://github.com/heroku/heroku-buildpack-python/compare/v285...v286
+[v285]: https://github.com/heroku/heroku-buildpack-python/compare/v284...v285
+[v284]: https://github.com/heroku/heroku-buildpack-python/compare/v283...v284
+[v283]: https://github.com/heroku/heroku-buildpack-python/compare/v282...v283
+[v282]: https://github.com/heroku/heroku-buildpack-python/compare/v281...v282
+[v281]: https://github.com/heroku/heroku-buildpack-python/compare/v280...v281
+[v280]: https://github.com/heroku/heroku-buildpack-python/compare/v279...v280
+[v279]: https://github.com/heroku/heroku-buildpack-python/compare/v278...v279
+[v278]: https://github.com/heroku/heroku-buildpack-python/compare/v277...v278
+[v277]: https://github.com/heroku/heroku-buildpack-python/compare/v276...v277
+[v276]: https://github.com/heroku/heroku-buildpack-python/compare/v275...v276
+[v275]: https://github.com/heroku/heroku-buildpack-python/compare/v274...v275
+[v274]: https://github.com/heroku/heroku-buildpack-python/compare/v273...v274
+[v273]: https://github.com/heroku/heroku-buildpack-python/compare/v272...v273
+[v272]: https://github.com/heroku/heroku-buildpack-python/compare/v271...v272
+[v271]: https://github.com/heroku/heroku-buildpack-python/compare/v270...v271
+[v270]: https://github.com/heroku/heroku-buildpack-python/compare/v269...v270
+[v269]: https://github.com/heroku/heroku-buildpack-python/compare/v268...v269
+[v268]: https://github.com/heroku/heroku-buildpack-python/compare/v267...v268
+[v267]: https://github.com/heroku/heroku-buildpack-python/compare/v266...v267
+[v266]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v265...v266
+[v265]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v264...archive/v265
+[v264]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v263...archive/v264
+[v263]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v262...archive/v263
+[v262]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v261...archive/v262
+[v261]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v260...archive/v261
+[v260]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v259...archive/v260
+[v259]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v258...archive/v259
+[v258]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v257...archive/v258
+[v257]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v256...archive/v257
+[v256]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v255...archive/v256
+[v255]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v254...archive/v255
+[v254]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v253...archive/v254
+[v253]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v252...archive/v253
+[v252]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v251...archive/v252
+[v251]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v250...archive/v251
+[v250]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v249...archive/v250
+[v249]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v248...archive/v249
+[v248]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v247...archive/v248
+[v247]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v246...archive/v247
+[v246]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v245...archive/v246
+[v245]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v244...archive/v245
+[v244]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v243...archive/v244
+[v243]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v242...archive/v243
+[v242]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v241...archive/v242
+[v241]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v240...archive/v241
+[v240]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v239...archive/v240
+[v239]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v238...archive/v239
+[v238]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v237...archive/v238
+[v237]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v236...archive/v237
+[v236]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v235...archive/v236
+[v235]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v234...archive/v235
+[v234]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v233...archive/v234
+[v233]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v232...archive/v233
+[v232]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v231...archive/v232
+[v231]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v230...archive/v231
+[v230]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v229...archive/v230
+[v229]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v228...archive/v229
+[v228]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v227...archive/v228
+[v227]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v226...archive/v227
+[v226]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v225...archive/v226
+[v225]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v224...archive/v225
+[v224]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v223...archive/v224
+[v223]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v222...archive/v223
+[v222]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v221...archive/v222
+[v221]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v220...archive/v221
+[v220]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v219...archive/v220
+[v219]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v218...archive/v219
+[v218]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v217...archive/v218
+[v217]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v216...archive/v217
+[v216]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v215...archive/v216
+[v215]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v214...archive/v215
+[v214]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v213...archive/v214
+[v213]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v212...archive/v213
+[v212]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v211...archive/v212
+[v211]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v210...archive/v211
+[v210]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v209...archive/v210
+[v209]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v208...archive/v209
+[v208]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v207...archive/v208
 [v207]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v206...archive/v207
 [v206]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v205...archive/v206
 [v205]: https://github.com/heroku/heroku-buildpack-python/compare/archive/v204...archive/v205
diff --git a/CODE_OF_CONDUCT.md b/CODE_OF_CONDUCT.md
new file mode 100644
index 000000000..9e229777d
--- /dev/null
+++ b/CODE_OF_CONDUCT.md
@@ -0,0 +1,105 @@
+# Salesforce Open Source Community Code of Conduct
+
+## About the Code of Conduct
+
+Equality is a core value at Salesforce. We believe a diverse and inclusive
+community fosters innovation and creativity, and are committed to building a
+culture where everyone feels included.
+
+Salesforce open-source projects are committed to providing a friendly, safe, and
+welcoming environment for all, regardless of gender identity and expression,
+sexual orientation, disability, physical appearance, body size, ethnicity, nationality,
+race, age, religion, level of experience, education, socioeconomic status, or
+other similar personal characteristics.
+
+The goal of this code of conduct is to specify a baseline standard of behavior so
+that people with different social values and communication styles can work
+together effectively, productively, and respectfully in our open source community.
+It also establishes a mechanism for reporting issues and resolving conflicts.
+
+All questions and reports of abusive, harassing, or otherwise unacceptable behavior
+in a Salesforce open-source project may be reported by contacting the Salesforce
+Open Source Conduct Committee at ossconduct@salesforce.com.
+
+## Our Pledge
+
+In the interest of fostering an open and welcoming environment, we as
+contributors and maintainers pledge to making participation in our project and
+our community a harassment-free experience for everyone, regardless of gender
+identity and expression, sexual orientation, disability, physical appearance,
+body size, ethnicity, nationality, race, age, religion, level of experience, education,
+socioeconomic status, or other similar personal characteristics.
+
+## Our Standards
+
+Examples of behavior that contributes to creating a positive environment
+include:
+
+* Using welcoming and inclusive language
+* Being respectful of differing viewpoints and experiences
+* Gracefully accepting constructive criticism
+* Focusing on what is best for the community
+* Showing empathy toward other community members
+
+Examples of unacceptable behavior by participants include:
+
+* The use of sexualized language or imagery and unwelcome sexual attention or
+advances
+* Personal attacks, insulting/derogatory comments, or trolling
+* Public or private harassment
+* Publishing, or threatening to publish, others' private information—such as
+a physical or electronic address—without explicit permission
+* Other conduct which could reasonably be considered inappropriate in a
+professional setting
+* Advocating for or encouraging any of the above behaviors
+
+## Our Responsibilities
+
+Project maintainers are responsible for clarifying the standards of acceptable
+behavior and are expected to take appropriate and fair corrective action in
+response to any instances of unacceptable behavior.
+
+Project maintainers have the right and responsibility to remove, edit, or
+reject comments, commits, code, wiki edits, issues, and other contributions
+that are not aligned with this Code of Conduct, or to ban temporarily or
+permanently any contributor for other behaviors that they deem inappropriate,
+threatening, offensive, or harmful.
+
+## Scope
+
+This Code of Conduct applies both within project spaces and in public spaces
+when an individual is representing the project or its community. Examples of
+representing a project or community include using an official project email
+address, posting via an official social media account, or acting as an appointed
+representative at an online or offline event. Representation of a project may be
+further defined and clarified by project maintainers.
+
+## Enforcement
+
+Instances of abusive, harassing, or otherwise unacceptable behavior may be
+reported by contacting the Salesforce Open Source Conduct Committee
+at ossconduct@salesforce.com. All complaints will be reviewed and investigated
+and will result in a response that is deemed necessary and appropriate to the
+circumstances. The committee is obligated to maintain confidentiality with
+regard to the reporter of an incident. Further details of specific enforcement
+policies may be posted separately.
+
+Project maintainers who do not follow or enforce the Code of Conduct in good
+faith may face temporary or permanent repercussions as determined by other
+members of the project's leadership and the Salesforce Open Source Conduct
+Committee.
+
+## Attribution
+
+This Code of Conduct is adapted from the [Contributor Covenant][contributor-covenant-home],
+version 1.4, available at https://www.contributor-covenant.org/version/1/4/code-of-conduct.html.
+It includes adaptations and additions from [Go Community Code of Conduct][golang-coc],
+[CNCF Code of Conduct][cncf-coc], and [Microsoft Open Source Code of Conduct][microsoft-coc].
+
+This Code of Conduct is licensed under the [Creative Commons Attribution 3.0 License][cc-by-3-us].
+
+[contributor-covenant-home]: https://www.contributor-covenant.org
+[golang-coc]: https://golang.org/conduct
+[cncf-coc]: https://github.com/cncf/foundation/blob/master/code-of-conduct.md
+[microsoft-coc]: https://opensource.microsoft.com/codeofconduct/
+[cc-by-3-us]: https://creativecommons.org/licenses/by/3.0/us/
diff --git a/Gemfile b/Gemfile
index 6bd480a38..7ed84f7d1 100644
--- a/Gemfile
+++ b/Gemfile
@@ -2,7 +2,7 @@
 
 source 'https://rubygems.org'
 
-ruby '>= 3.1', '< 3.4'
+ruby '>= 3.2', '< 4.1'
 
 group :test, :development do
   gem 'heroku_hatchet'
diff --git a/Gemfile.lock b/Gemfile.lock
index 90b394edb..36e3c353f 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,11 +1,12 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    ast (2.4.2)
-    base64 (0.2.0)
-    diff-lcs (1.5.1)
+    ast (2.4.3)
+    base64 (0.3.0)
+    diff-lcs (1.6.2)
     erubis (2.7.0)
-    excon (0.110.0)
+    excon (1.5.0)
+      logger
     heroics (0.1.3)
       base64
       erubis (~> 2.0)
@@ -13,66 +14,73 @@ GEM
       moneta
       multi_json (>= 1.9.2)
       webrick
-    heroku_hatchet (8.0.4)
-      excon (~> 0)
+    heroku_hatchet (8.0.6)
+      excon (< 2)
       platform-api (~> 3)
       rrrretry (~> 1)
       thor (~> 1)
       threaded (~> 0)
-    json (2.7.2)
-    language_server-protocol (3.17.0.3)
+    json (2.20.0)
+    language_server-protocol (3.17.0.5)
+    lint_roller (1.1.0)
+    logger (1.7.0)
     moneta (1.0.0)
-    multi_json (1.15.0)
-    parallel (1.25.1)
+    multi_json (1.21.1)
+    parallel (2.1.0)
     parallel_split_test (0.10.0)
       parallel (>= 0.5.13)
       rspec-core (>= 3.9.0)
-    parser (3.3.3.0)
+    parser (3.3.11.1)
       ast (~> 2.4.1)
       racc
-    platform-api (3.7.0)
+    platform-api (3.9.0)
       heroics (~> 0.1.1)
       moneta (~> 1.0.0)
       rate_throttle_client (~> 0.1.0)
-    racc (1.8.0)
+    prism (1.9.0)
+    racc (1.8.1)
     rainbow (3.1.1)
     rate_throttle_client (0.1.2)
-    regexp_parser (2.9.2)
-    rexml (3.3.0)
-      strscan
+    regexp_parser (2.12.0)
     rrrretry (1.0.0)
-    rspec-core (3.13.0)
+    rspec-core (3.13.6)
       rspec-support (~> 3.13.0)
-    rspec-expectations (3.13.1)
+    rspec-expectations (3.13.5)
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.13.0)
     rspec-retry (0.6.2)
       rspec-core (> 3.3)
-    rspec-support (3.13.1)
-    rubocop (1.64.1)
+    rspec-support (3.13.7)
+    rubocop (1.88.1)
       json (~> 2.3)
-      language_server-protocol (>= 3.17.0)
-      parallel (~> 1.10)
+      language_server-protocol (~> 3.17.0.2)
+      lint_roller (~> 1.1.0)
+      parallel (>= 1.10)
       parser (>= 3.3.0.2)
       rainbow (>= 2.2.2, < 4.0)
-      regexp_parser (>= 1.8, < 3.0)
-      rexml (>= 3.2.5, < 4.0)
-      rubocop-ast (>= 1.31.1, < 2.0)
+      regexp_parser (>= 2.9.3, < 3.0)
+      rubocop-ast (>= 1.49.0, < 2.0)
       ruby-progressbar (~> 1.7)
-      unicode-display_width (>= 2.4.0, < 3.0)
-    rubocop-ast (1.31.3)
-      parser (>= 3.3.1.0)
-    rubocop-rspec (3.0.1)
-      rubocop (~> 1.61)
+      unicode-display_width (>= 2.4.0, < 4.0)
+    rubocop-ast (1.49.1)
+      parser (>= 3.3.7.2)
+      prism (~> 1.7)
+    rubocop-rspec (3.10.2)
+      lint_roller (~> 1.1)
+      regexp_parser (>= 2.0)
+      rubocop (~> 1.86, >= 1.86.2)
     ruby-progressbar (1.13.0)
-    strscan (3.1.0)
-    thor (1.3.1)
+    thor (1.5.0)
     threaded (0.0.4)
-    unicode-display_width (2.5.0)
-    webrick (1.8.1)
+    unicode-display_width (3.2.0)
+      unicode-emoji (~> 4.1)
+    unicode-emoji (4.2.0)
+    webrick (1.9.2)
 
 PLATFORMS
+  arm64-darwin-24
   ruby
+  x86_64-linux
 
 DEPENDENCIES
   heroku_hatchet
@@ -83,8 +91,47 @@ DEPENDENCIES
   rubocop
   rubocop-rspec
 
+CHECKSUMS
+  ast (2.4.3) sha256=954615157c1d6a382bc27d690d973195e79db7f55e9765ac7c481c60bdb4d383
+  base64 (0.3.0) sha256=27337aeabad6ffae05c265c450490628ef3ebd4b67be58257393227588f5a97b
+  bundler (4.0.13) sha256=19f08be7f27022cf0b89f27da0b044ae075e8270a9ef44ad248a932614e1ca3b
+  diff-lcs (1.6.2) sha256=9ae0d2cba7d4df3075fe8cd8602a8604993efc0dfa934cff568969efb1909962
+  erubis (2.7.0) sha256=63653f5174a7997f6f1d6f465fbe1494dcc4bdab1fb8e635f6216989fb1148ba
+  excon (1.5.0) sha256=c503ad1d0123bc8ab2a062ff3789dc891ec368cb9e13765ab88a9c58c8bb6d50
+  heroics (0.1.3) sha256=31d792e8706ecc6f78299f52d0b0f8ab55489a13b5f4f76c3050b07912563562
+  heroku_hatchet (8.0.6) sha256=886a7d7d686859db9fac19df1194a35c5349285956ca4d134054c5c376accea3
+  json (2.20.0) sha256=9362bc6e55a952b056abf9167cf053358181c904cb70cd6eee0808ea830fc32b
+  language_server-protocol (3.17.0.5) sha256=fd1e39a51a28bf3eec959379985a72e296e9f9acfce46f6a79d31ca8760803cc
+  lint_roller (1.1.0) sha256=2c0c845b632a7d172cb849cc90c1bce937a28c5c8ccccb50dfd46a485003cc87
+  logger (1.7.0) sha256=196edec7cc44b66cfb40f9755ce11b392f21f7967696af15d274dde7edff0203
+  moneta (1.0.0) sha256=2224e5a68156e8eceb525fb0582c8c4e0f29f67cae86507cdcfb406abbb1fc5d
+  multi_json (1.21.1) sha256=e6126a31808e3b4d19f483c775ceac34df190dffa62adfb63a165ee14ba68080
+  parallel (2.1.0) sha256=b35258865c2e31134c5ecb708beaaf6772adf9d5efae28e93e99260877b09356
+  parallel_split_test (0.10.0) sha256=4abd6bedc6a1b169ecb93a1bf982fa7fbd437b66c360594d56d107c25f53b05f
+  parser (3.3.11.1) sha256=d17ace7aabe3e72c3cc94043714be27cc6f852f104d81aa284c2281aecc65d54
+  platform-api (3.9.0) sha256=be3b919955c52649fd931a9f62d571bd6f06613de630970dc7255fc95eb7d962
+  prism (1.9.0) sha256=7b530c6a9f92c24300014919c9dcbc055bf4cdf51ec30aed099b06cd6674ef85
+  racc (1.8.1) sha256=4a7f6929691dbec8b5209a0b373bc2614882b55fc5d2e447a21aaa691303d62f
+  rainbow (3.1.1) sha256=039491aa3a89f42efa1d6dec2fc4e62ede96eb6acd95e52f1ad581182b79bc6a
+  rate_throttle_client (0.1.2) sha256=f9de968b892fea9272154f6182b4f5cfb74292585e66763fb8a8510181ec83ee
+  regexp_parser (2.12.0) sha256=35a916a1d63190ab5c9009457136ae5f3c0c7512d60291d0d1378ba18ce08ebb
+  rrrretry (1.0.0) sha256=3c60784501701a49d8ad499af7e76dbddf9a8be916beffe885bd0f443ad1c749
+  rspec-core (3.13.6) sha256=a8823c6411667b60a8bca135364351dda34cd55e44ff94c4be4633b37d828b2d
+  rspec-expectations (3.13.5) sha256=33a4d3a1d95060aea4c94e9f237030a8f9eae5615e9bd85718fe3a09e4b58836
+  rspec-retry (0.6.2) sha256=6101ba23a38809811ae3484acde4ab481c54d846ac66d5037ccb40131a60d858
+  rspec-support (3.13.7) sha256=0640e5570872aafefd79867901deeeeb40b0c9875a36b983d85f54fb7381c47c
+  rubocop (1.88.1) sha256=726af773d6bc169ed3ff852f3ca020b7c58d39c34e7a8d879a8e0147cc994f26
+  rubocop-ast (1.49.1) sha256=4412f3ee70f6fe4546cc489548e0f6fcf76cafcfa80fa03af67098ffed755035
+  rubocop-rspec (3.10.2) sha256=0b3e2ecc592cd10ecbf0095bb58d1e357905276e069643523cc19eb7495f65e2
+  ruby-progressbar (1.13.0) sha256=80fc9c47a9b640d6834e0dc7b3c94c9df37f08cb072b7761e4a71e22cff29b33
+  thor (1.5.0) sha256=e3a9e55fe857e44859ce104a84675ab6e8cd59c650a49106a05f55f136425e73
+  threaded (0.0.4) sha256=8f32c11d29f7c7237aabeb36d286c15ac495137ce06ace3357de743aafd4f0e3
+  unicode-display_width (3.2.0) sha256=0cdd96b5681a5949cdbc2c55e7b420facae74c4aaf9a9815eee1087cb1853c42
+  unicode-emoji (4.2.0) sha256=519e69150f75652e40bf736106cfbc8f0f73aa3fb6a65afe62fefa7f80b0f80f
+  webrick (1.9.2) sha256=beb4a15fc474defed24a3bda4ffd88a490d517c9e4e6118c3edce59e45864131
+
 RUBY VERSION
-   ruby 3.3.2p78
+  ruby 4.0.5
 
 BUNDLED WITH
-   2.5.11
+  4.0.13
diff --git a/Makefile b/Makefile
index 3e36a4eb4..f1afaf93d 100644
--- a/Makefile
+++ b/Makefile
@@ -1,13 +1,15 @@
 # These targets are not files
-.PHONY: lint lint-scripts lint-ruby run publish
+.PHONY: lint lint-scripts lint-ruby check-format format run publish
 
-STACK ?= heroku-24
+STACK ?= heroku-26
 FIXTURE ?= spec/fixtures/python_version_unspecified
+# Allow overriding the exit code in CI, so we can test bin/report works for failing builds.
+COMPILE_FAILURE_EXIT_CODE ?= 1
 
 # Converts a stack name of `heroku-NN` to its build Docker image tag of `heroku/heroku:NN-build`.
 STACK_IMAGE_TAG := heroku/$(subst -,:,$(STACK))-build
 
-lint: lint-scripts lint-ruby
+lint: lint-scripts check-format lint-ruby
 
 lint-scripts:
 	@git ls-files -z --cached --others --exclude-standard 'bin/*' '*/bin/*' '*.sh' | xargs -0 shellcheck --check-sourced --color=always
@@ -15,17 +17,31 @@ lint-scripts:
 lint-ruby:
 	@bundle exec rubocop
 
+check-format:
+	@shfmt --diff .
+
+format:
+	@shfmt --write --list .
+
 run:
 	@echo "Running buildpack using: STACK=$(STACK) FIXTURE=$(FIXTURE)"
-	@docker run --rm -it -v $(PWD):/src:ro --tmpfs /app -e "HOME=/app" -e "STACK=$(STACK)" "$(STACK_IMAGE_TAG)" \
-		bash -eo pipefail -c '\
-			mkdir /tmp/buildpack /tmp/build /tmp/cache /tmp/env \
-			&& cp -r /src/{bin,lib,requirements,vendor} /tmp/buildpack \
-			&& cp -rT /src/$(FIXTURE) /tmp/build \
-			&& cd /tmp/buildpack \
-			&& echo -e "\n~ Detect:" && bash ./bin/detect /tmp/build /tmp/cache /tmp/env \
-			&& echo -e "\n~ Compile:" && { ./bin/compile /tmp/build /tmp/cache /tmp/env || true; } \
-			&& echo -e "\n~ Report:" && ./bin/report /tmp/build /tmp/cache /tmp/env \
+	@docker run --rm -v $(PWD):/src:ro --tmpfs /app:mode=1777 -e "HOME=/app" -e "STACK=$(STACK)" "$(STACK_IMAGE_TAG)" \
+		bash -euo pipefail -O dotglob -c '\
+			mkdir /tmp/buildpack /tmp/cache /tmp/env; \
+			cp -r /src/{bin,lib,requirements,vendor} /tmp/buildpack; \
+			cp -r /src/$(FIXTURE) /tmp/build_1; \
+			cd /tmp/buildpack; \
+			unset $$(printenv | cut -d '=' -f 1 | grep -vE "^(HOME|LANG|PATH|STACK)$$"); \
+			echo -en "\n~ Detect: " && ./bin/detect /tmp/build_1; \
+			echo -e "\n~ Compile:" && { ./bin/compile /tmp/build_1 /tmp/cache /tmp/env || COMPILE_FAILED=1; }; \
+			echo -e "\n~ Report:" && ./bin/report /tmp/build_1 /tmp/cache /tmp/env; \
+			[[ "$${COMPILE_FAILED:-}" == "1" ]] && exit $(COMPILE_FAILURE_EXIT_CODE); \
+			[[ -f /tmp/build_1/bin/compile ]] && { echo -e "\n~ Compile (Inline Buildpack):" && (source ./export && /tmp/build_1/bin/compile /tmp/build_1 /tmp/cache /tmp/env); }; \
+			echo -e "\n~ Release:" && ./bin/release /tmp/build_1; \
+			rm -rf /app/* /tmp/buildpack/export /tmp/build_1; \
+			cp -r /src/$(FIXTURE) /tmp/build_2; \
+			echo -e "\n~ Recompile:" && ./bin/compile /tmp/build_2 /tmp/cache /tmp/env; \
+			echo -e "\nBuild successful!"; \
 		'
 	@echo
 
diff --git a/README.md b/README.md
index 32dc35a58..4f8703ea4 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,4 @@
-![python](https://cloud.githubusercontent.com/assets/51578/13712821/b68a42ce-e793-11e5-96b0-d8eb978137ba.png)
+![python](https://raw.githubusercontent.com/heroku/buildpacks/refs/heads/main/assets/images/buildpack-banner-python.png)
 
 # Heroku Buildpack: Python
 
@@ -8,60 +8,57 @@ This is the official [Heroku buildpack](https://devcenter.heroku.com/articles/bu
 
 Recommended web frameworks include **Django** and **Flask**, among others. The recommended webserver is **Gunicorn**. There are no restrictions around what software can be used (as long as it's pip-installable). Web processes must bind to `$PORT`, and only the HTTP protocol is permitted for incoming connections.
 
-See it in Action
-----------------
-```
-$ ls
-my-application		requirements.txt	runtime.txt
-
-$ git push heroku main
-Counting objects: 4, done.
-Delta compression using up to 8 threads.
-Compressing objects: 100% (2/2), done.
-Writing objects: 100% (4/4), 276 bytes | 276.00 KiB/s, done.
-Total 4 (delta 0), reused 0 (delta 0)
-remote: Compressing source files... done.
-remote: Building source:
-remote:
-remote: -----> Python app detected
-remote: -----> Installing python
-remote: -----> Installing pip
-remote: -----> Installing SQLite3
-remote: -----> Installing requirements with pip
-remote:        Collecting flask (from -r /tmp/build_c2c067ef79ff14c9bf1aed6796f9ed1f/requirements.txt (line 1))
-remote:          Downloading ...
-remote:        Installing collected packages: Werkzeug, click, MarkupSafe, Jinja2, itsdangerous, flask
-remote:        Successfully installed Jinja2-2.10 MarkupSafe-1.1.0 Werkzeug-0.14.1 click-7.0 flask-1.0.2 itsdangerous-1.1.0
-remote:
-remote: -----> Discovering process types
-remote:        Procfile declares types -> (none)
-remote:
-```
-
-A `requirements.txt` must be present at the root of your application's repository to deploy.
-
-To specify your python version, you also need a `runtime.txt` file - unless you are using the default Python runtime version.
-
-Current default Python Runtime: Python 3.12.4
-
-Alternatively, you can provide a `setup.py` file, or a `Pipfile`.
-Using `pipenv` will generate `runtime.txt` at build time if one of the field `python_version` or `python_full_version` is specified in the `requires` section of your `Pipfile`.
-
-Specify a Buildpack Version
----------------------------
-
-You can specify the latest production release of this buildpack for upcoming builds of an existing application:
-
-    $ heroku buildpacks:set heroku/python
-
-
-Specify a Python Runtime
-------------------------
-
-Supported runtime options include:
-
-- `python-3.12.4` on all [supported stacks](https://devcenter.heroku.com/articles/stack#stack-support-details)
-- `python-3.11.9` on all [supported stacks](https://devcenter.heroku.com/articles/stack#stack-support-details)
-- `python-3.10.14` on all [supported stacks](https://devcenter.heroku.com/articles/stack#stack-support-details)
-- `python-3.9.19` on Heroku-20 and Heroku-22 only
-- `python-3.8.19` on Heroku-20 only
+## Getting Started
+
+See the [Getting Started on Heroku with Python](https://devcenter.heroku.com/articles/getting-started-with-python) tutorial.
+
+## Application Requirements
+
+A `requirements.txt`, `Pipfile.lock`, `poetry.lock`, or `uv.lock` file must be present in the root (top-level)
+directory of your app's source code.
+
+When using the package manager [uv](https://docs.astral.sh/uv/) a `.python-version` file is also required.
+
+## Configuration
+
+### Python Version
+
+We recommend that you specify a Python version for your app rather than relying on the buildpack's default Python version.
+
+For example, to request the latest patch release of Python 3.14, create a `.python-version` file in
+the root directory of your app containing:
+`3.14`
+
+We strongly recommend that you use the major version form instead of pinning to an exact version,
+since it will allow your app to receive Python security updates.
+
+The buildpack will look for a Python version in the following places (in descending order of precedence):
+
+1. `runtime.txt` file (deprecated)
+2. `.python-version` file (recommended)
+3. The `python_full_version` field in the `Pipfile.lock` file
+4. The `python_version` field in the `Pipfile.lock` file
+
+If none of those are found, the buildpack will use a default Python version for the first
+build of an app, and then subsequent builds of that app will be pinned to that version
+unless the build cache is cleared or you request a different version.
+
+The current default Python version is: 3.14
+
+The supported Python versions are:
+
+- Python 3.14
+- Python 3.13
+- Python 3.12
+- Python 3.11
+
+These Python versions are deprecated on Heroku:
+
+- Python 3.10
+
+Python versions older than those listed above are no longer supported, since they have reached
+end-of-life [upstream](https://devguide.python.org/versions/#supported-versions).
+
+## Documentation
+
+For more information about using Python on Heroku, see [Dev Center](https://devcenter.heroku.com/categories/python-support).
diff --git a/SECURITY.md b/SECURITY.md
new file mode 100644
index 000000000..72541d6bd
--- /dev/null
+++ b/SECURITY.md
@@ -0,0 +1,7 @@
+# Security
+
+Please report any security issue to [https://www.sfdc.co/SubmitVuln](https://www.sfdc.co/SubmitVuln)
+as soon as it is discovered. This project limits its runtime dependencies in
+order to reduce the total cost of ownership as much as can be, but all consumers
+should remain vigilant and have their security stakeholders review all third-party
+products (3PP) like this one and their dependencies.
diff --git a/bin/compile b/bin/compile
index f9c219c0c..7017cabf3 100755
--- a/bin/compile
+++ b/bin/compile
@@ -2,9 +2,15 @@
 # Usage: bin/compile <build-dir> <cache-dir> <env-dir>
 # See: https://devcenter.heroku.com/articles/buildpack-api
 
-set -eo pipefail
-
-[[ -n "$BUILDPACK_XTRACE" ]] && set -o xtrace
+# We use `errtrace` and `inherit_errexit` to ensure the ERR trap and exit on error behaviour
+# propagates to buildpack functions run in subshells, such as when using command substitutions.
+set -eu -o pipefail -o errtrace
+shopt -s inherit_errexit
+
+# Note: This can't be enabled via app config vars, since at this point they haven't been loaded from ENV_DIR.
+if [[ "${BUILDPACK_XTRACE:-0}" == "1" ]]; then
+	set -o xtrace
+fi
 
 BUILD_DIR="${1}"
 CACHE_DIR="${2}"
@@ -14,37 +20,35 @@ ENV_DIR="${3}"
 BUILDPACK_DIR=$(cd "$(dirname "$(dirname "${BASH_SOURCE[0]}")")" && pwd)
 
 source "${BUILDPACK_DIR}/bin/utils"
-source "${BUILDPACK_DIR}/lib/metadata.sh"
-
-compile_start_time=$(nowms)
-
-# Initialise metadata store.
-meta_init "${CACHE_DIR}" "python"
-meta_setup
-
-# Prepend proper path for old-school virtualenv hackery.
-# This may not be necessary.
-export PATH=:/usr/local/bin:$PATH
+source "${BUILDPACK_DIR}/lib/utils.sh"
+source "${BUILDPACK_DIR}/lib/build_data.sh"
+source "${BUILDPACK_DIR}/lib/cache.sh"
+source "${BUILDPACK_DIR}/lib/checks.sh"
+source "${BUILDPACK_DIR}/lib/hooks.sh"
+source "${BUILDPACK_DIR}/lib/output.sh"
+source "${BUILDPACK_DIR}/lib/package_manager.sh"
+source "${BUILDPACK_DIR}/lib/pip.sh"
+source "${BUILDPACK_DIR}/lib/pipenv.sh"
+source "${BUILDPACK_DIR}/lib/poetry.sh"
+source "${BUILDPACK_DIR}/lib/python_version.sh"
+source "${BUILDPACK_DIR}/lib/python.sh"
+source "${BUILDPACK_DIR}/lib/uv.sh"
+
+compile_start_time=$(build_data::current_unix_realtime)
+
+# Initialise the build data store used to track state across builds (for cache invalidation
+# and messaging when build configuration changes) and also so that `bin/report` can generate
+# a build report that will be consumed by the build system for observability.
+build_data::setup
+
+trap 'utils::err_trap' ERR
+
+checks::ensure_supported_stack "${STACK:?"Required env var STACK isn't set"}"
+checks::duplicate_python_buildpack "${BUILD_DIR}"
 
 # Exported for use in subshells, such as the steps run via sub_env.
 export BUILD_DIR CACHE_DIR ENV_DIR
 
-# Set the base URL for downloading buildpack assets like Python runtimes.
-# The user can provide BUILDPACK_S3_BASE_URL to specify a custom target.
-# Note: this is designed for non-Heroku use, as it does not use the user-provided
-# environment variable mechanism (the ENV_DIR).
-S3_BASE_URL="${BUILDPACK_S3_BASE_URL:-"https://heroku-buildpack-python.s3.us-east-1.amazonaws.com"}"
-# This has to be exported since it's used by the geo-libs step which is run in a subshell.
-
-# Default Python Versions
-source "${BUILDPACK_DIR}/bin/default_pythons"
-
-# Common Problem Warnings:
-# This section creates a temporary file in which to stick the output of `pip install`.
-# The `warnings` subscript then greps through this for common problems and guides
-# the user towards resolution of known issues.
-WARNINGS_LOG=$(mktemp)
-
 # Sanitize externally-provided environment variables:
 # The following environment variables are either problematic or simply unnecessary
 # for the buildpack to have knowledge of, so we unset them, to keep the environment
@@ -52,7 +56,6 @@ WARNINGS_LOG=$(mktemp)
 unset PYTHONHOME PYTHONPATH
 
 # Import the warnings script, which contains the `pip install` user warning mechanisms
-# (mentioned and explained above)
 source "${BUILDPACK_DIR}/bin/warnings"
 
 # Make the directory in which we will create symlinks from the temporary build directory
@@ -61,268 +64,244 @@ source "${BUILDPACK_DIR}/bin/warnings"
 # More on this topic later.
 mkdir -p /app/.heroku
 
-PROFILE_PATH="$BUILD_DIR/.profile.d/python.sh"
+PROFILE_PATH="${BUILD_DIR}/.profile.d/python.sh"
 EXPORT_PATH="${BUILDPACK_DIR}/export"
-GUNICORN_PROFILE_PATH="$BUILD_DIR/.profile.d/python.gunicorn.sh"
-WEB_CONCURRENCY_PROFILE_PATH="$BUILD_DIR/.profile.d/WEB_CONCURRENCY.sh"
-
-export PATH=/app/.heroku/python/bin:/app/.heroku/vendor/bin:$PATH
-# Tell Python to not buffer it's stdin/stdout.
+GUNICORN_PROFILE_PATH="${BUILD_DIR}/.profile.d/python.gunicorn.sh"
+WEB_CONCURRENCY_PROFILE_PATH="${BUILD_DIR}/.profile.d/WEB_CONCURRENCY.sh"
+python_home='/app/.heroku/python'
+
+# NB: Python must be added to PATH using the symlinked `/app` location and not its actual location
+# in BUILD_DIR, so that Python reports its location (via `sys.prefix`, `sys.executable` and others)
+# using `/app` paths which will still work at run-time after relocation. Amongst other things, this
+# ensures that the shebang lines in the entrypoint scripts of installed packages are correct.
+export PATH="/app/.heroku/python/bin:${PATH}"
+# Disable Python's output buffering to ensure logs aren't dropped if an app crashes.
 export PYTHONUNBUFFERED=1
-# Set the locale to a well-known and expected standard.
-export LANG=en_US.UTF-8
-# `~/.heroku/vendor` is an place where the buildpack may stick pre-build binaries for known
-# C dependencies. This section configures Python (GCC, more specifically)
-# and pip to automatically include these paths when building binaries.
-# TODO: Stop adding .heroku/vendor here now that the buildpack no longer vendors anything.
-export C_INCLUDE_PATH=/app/.heroku/vendor/include:/app/.heroku/python/include:$C_INCLUDE_PATH
-export CPLUS_INCLUDE_PATH=/app/.heroku/vendor/include:/app/.heroku/python/include:$CPLUS_INCLUDE_PATH
-export LIBRARY_PATH=/app/.heroku/vendor/lib:/app/.heroku/python/lib:$LIBRARY_PATH
-export LD_LIBRARY_PATH=/app/.heroku/vendor/lib:/app/.heroku/python/lib:$LD_LIBRARY_PATH
-export PKG_CONFIG_PATH=/app/.heroku/vendor/lib/pkg-config:/app/.heroku/python/lib/pkg-config:$PKG_CONFIG_PATH
-
-# Global pip options (https://pip.pypa.io/en/stable/user_guide/#environment-variables).
-# Disable pip's warnings about EOL Python since we show our own.
-export PIP_NO_PYTHON_VERSION_WARNING=1
-
-cd "$BUILD_DIR"
-
-# The Cache
-# ---------
-
-# The workflow for the Python Buildpack's cache is as follows:
-#
-# - `~/.heroku/{known-paths}` are copied from the cache into the slug.
-# - The build is executed, modifying `~/.heroku/{known-paths}`.
-# - Once the build is complete, `~/.heroku/{known-paths}` is copied back into the cache.
-
-# Create the cache directory, if it doesn't exist.
-mkdir -p "$CACHE_DIR/.heroku"
-
-# Restore old artifacts from the cache.
-mkdir -p .heroku
-
-# The Python installation.
-cp -R "$CACHE_DIR/.heroku/python" .heroku/ &> /dev/null || true
-# A plain text file which contains the current stack being used (used for cache busting).
-cp -R "$CACHE_DIR/.heroku/python-stack" .heroku/ &> /dev/null || true
-# A plain text file which contains the current python version being used (used for cache busting).
-cp -R "$CACHE_DIR/.heroku/python-version" .heroku/ &> /dev/null || true
-# A plain text file which contains the current sqlite3 version being used (used for cache busting).
-cp -R "$CACHE_DIR/.heroku/python-sqlite3-version" .heroku/ &> /dev/null || true
-# "editable" installations of code repositories, via pip or pipenv.
-if [[ -d "$CACHE_DIR/.heroku/src" ]]; then
-  cp -R "$CACHE_DIR/.heroku/src" .heroku/ &> /dev/null || true
-fi
-
-# The pre_compile hook. Customers rely on this. Don't remove it.
-# This part of the code is used to allow users to customize their build experience
-# without forking the buildpack by providing a `bin/pre_compile` script, which gets
-# run inline with the buildpack automatically.
-source "${BUILDPACK_DIR}/bin/steps/hooks/pre_compile"
-
-# Sticky runtimes. If there was a previous build, and it used a given version of Python,
-# continue to use that version of Python in perpetuity.
-if [[ -f "$CACHE_DIR/.heroku/python-version" ]]; then
-  CACHED_PYTHON_VERSION=$(cat "$CACHE_DIR/.heroku/python-version")
-fi
-
-# We didn't always record the stack version. This code is in place because of that.
-if [[ -f "$CACHE_DIR/.heroku/python-stack" ]]; then
-  CACHED_PYTHON_STACK=$(cat "$CACHE_DIR/.heroku/python-stack")
+# Ensure Python uses a Unicode locale, to prevent the issues described in:
+# https://github.com/docker-library/python/pull/570
+export LANG="en_US.UTF-8"
+export C_INCLUDE_PATH="/app/.heroku/python/include${C_INCLUDE_PATH:+:${C_INCLUDE_PATH}}"
+export CPLUS_INCLUDE_PATH="/app/.heroku/python/include${CPLUS_INCLUDE_PATH:+:${CPLUS_INCLUDE_PATH}}"
+export LIBRARY_PATH="/app/.heroku/python/lib${LIBRARY_PATH:+:${LIBRARY_PATH}}"
+export LD_LIBRARY_PATH="/app/.heroku/python/lib${LD_LIBRARY_PATH:+:${LD_LIBRARY_PATH}}"
+export PKG_CONFIG_PATH="/app/.heroku/python/lib/pkg-config${PKG_CONFIG_PATH:+:${PKG_CONFIG_PATH}}"
+
+cd "${BUILD_DIR}"
+
+# Runs a `bin/pre_compile` script if found in the app source, allowing build customisation.
+hooks::run_hook "pre_compile"
+
+# These later checks are after the pre_compile hook so that we can check not only the
+# original app source, but also that the hook hasn't written to these locations either.
+checks::existing_python_dir_present "${BUILD_DIR}"
+
+package_manager="$(package_manager::determine_package_manager "${BUILD_DIR}")"
+build_data::set_string "package_manager" "${package_manager}"
+
+# This check is after the package manager step to improve the UX when the package manager file
+# is missing and the venv directory was the only reason the buildpack passed detection.
+# (Since once they remove the venv detection will fail, which would prevent us from being able
+# to display the more helpful "missing package manager file" error message on the next build).
+checks::existing_venv_dir_present "${BUILD_DIR}"
+
+cached_python_full_version="$(cache::cached_python_full_version "${CACHE_DIR}")"
+
+# We use the Bash 4.3+ `nameref` feature to pass back multiple values from this function
+# without having to hardcode globals. See: https://stackoverflow.com/a/38997681
+python_version::read_requested_python_version "${BUILD_DIR}" "${package_manager}" "${cached_python_full_version}" requested_python_version python_version_origin
+build_data::set_string "python_version_requested" "${requested_python_version}"
+build_data::set_string "python_version_origin" "${python_version_origin}"
+
+case "${python_version_origin}" in
+	default)
+		output::step "No Python version was specified. Using the buildpack default: Python ${requested_python_version}"
+		;;
+	cached)
+		output::step "No Python version was specified. Using the same major version as the last build: Python ${requested_python_version}"
+		;;
+	*)
+		output::step "Using Python ${requested_python_version} specified in ${python_version_origin}"
+		;;
+esac
+
+python_full_version="$(python_version::resolve_python_version "${requested_python_version}" "${python_version_origin}")"
+python_major_version="${python_full_version%.*}"
+build_data::set_string "python_version" "${python_full_version}"
+build_data::set_string "python_version_major" "${python_major_version}"
+
+if [[ "${requested_python_version}" == "${python_full_version}" ]]; then
+	build_data::set_raw "python_version_pinned" "true"
 else
-  CACHED_PYTHON_STACK=$STACK
+	build_data::set_raw "python_version_pinned" "false"
 fi
 
-# TODO: Move this into a new package manager handling implementation when adding Poetry support.
-# We intentionally don't mention `setup.py` here since it's being removed soon.
-if [[ ! -f requirements.txt && ! -f Pipfile && ! -f setup.py ]]; then
-  puts-warn
-  puts-warn "Error: Couldn't find any supported Python package manager files."
-  puts-warn
-  puts-warn "A Python app on Heroku must have either a 'requirements.txt' or"
-  puts-warn "'Pipfile' package manager file in the root directory of its"
-  puts-warn "source code."
-  puts-warn
-  puts-warn "Currently the root directory of your app contains:"
-  puts-warn
-  # TODO: Overhaul logging helpers so they can handle prefixing multi-line strings, and switch to them.
-  # shellcheck disable=SC2012 # Using `ls` instead of `find` is absolutely fine for this use case.
-  ls -1 --indicator-style=slash "${BUILD_DIR}" | sed 's/^/ !     /'
-  puts-warn
-  puts-warn "If your app already has a package manager file, check that it:"
-  puts-warn
-  puts-warn "1. Is in the top level directory (not a subdirectory)."
-  puts-warn "2. Has the correct spelling (the filenames are case-sensitive)."
-  puts-warn "3. Isn't listed in '.gitignore' or '.slugignore'."
-  puts-warn
-  puts-warn "Otherwise, add a package manager file to your app. If your app has"
-  puts-warn "no dependencies, then create an empty 'requirements.txt' file."
-  puts-warn
-  puts-warn "For help with using Python on Heroku, see:"
-  puts-warn "https://devcenter.heroku.com/articles/getting-started-with-python"
-  puts-warn "https://devcenter.heroku.com/articles/python-support"
-  puts-warn
-  meta_set "failure_reason" "package-manager-not-found"
-  exit 1
-fi
+# We wait until after Python version resolution to show these warnings, to avoid causing confusion
+# as to what was a warning vs an error. In addition, several of the error messages contain similar
+# content to the warnings (such as encouraging use of .python-version and major version syntax),
+# which would mean duplicate content if we showed both.
+python_version::warn_or_error_if_python_version_file_missing "${python_version_origin}" "${python_major_version}" "${package_manager}"
+python_version::warn_if_deprecated_major_version "${python_major_version}" "${python_version_origin}"
+python_version::warn_if_patch_update_available "${python_full_version}" "${python_major_version}" "${python_version_origin}"
 
-# Pipenv Python version support.
-# Detect the version of Python requested from a Pipfile (e.g. python_version or python_full_version).
-# Convert it to a runtime.txt file.
-source "${BUILDPACK_DIR}/bin/steps/pipenv-python-version"
-
-if [[ -f runtime.txt ]]; then
-  # PYTHON_VERSION_SOURCE may have already been set by the pipenv-python-version step.
-  # TODO: Refactor this and stop pipenv-python-version using runtime.txt as an API.
-  PYTHON_VERSION_SOURCE=${PYTHON_VERSION_SOURCE:-"runtime.txt"}
-  puts-step "Using Python version specified in ${PYTHON_VERSION_SOURCE}"
-  meta_set "python_version_reason" "specified"
-elif [[ -n "${CACHED_PYTHON_VERSION:-}" ]]; then
-  puts-step "No Python version was specified. Using the same version as the last build: ${CACHED_PYTHON_VERSION}"
-  echo "       To use a different version, see: https://devcenter.heroku.com/articles/python-runtimes"
-  meta_set "python_version_reason" "cached"
-  echo "${CACHED_PYTHON_VERSION}" > runtime.txt
-else
-  puts-step "No Python version was specified. Using the buildpack default: ${DEFAULT_PYTHON_VERSION}"
-  echo "       To use a different version, see: https://devcenter.heroku.com/articles/python-runtimes"
-  meta_set "python_version_reason" "default"
-  echo "${DEFAULT_PYTHON_VERSION}" > runtime.txt
-fi
+cache::restore "${BUILD_DIR}" "${CACHE_DIR}" "${STACK}" "${cached_python_full_version}" "${python_full_version}" "${package_manager}"
 
-# Create the directory for .profile.d, if it doesn't exist.
-mkdir -p "$(dirname "$PROFILE_PATH")"
-# Create the directory for editable source code installation, if it doesn't exist.
-mkdir -p /app/.heroku/src
+# The directory for the .profile.d scripts.
+mkdir -p "$(dirname "${PROFILE_PATH}")"
 
 # On Heroku CI, builds happen in `/app`. Otherwise, on the Heroku platform,
 # they occur in a temp directory. Because Python is not portable, we must create
 # symlinks to emulate that we are operating in `/app` during the build process.
 # This is (hopefully obviously) because apps end up running from `/app` in production.
 # Realpath is used to support use-cases where one of the locations is a symlink to the other.
+# shellcheck disable=SC2312 # TODO: Invoke this command separately to avoid masking its return value.
 if [[ "$(realpath "${BUILD_DIR}")" != "$(realpath /app)" ]]; then
-    # python expects to reside in /app, so set up symlinks
-    # we will not remove these later so subsequent buildpacks can still invoke it
-    ln -nsf "$BUILD_DIR/.heroku/python" /app/.heroku/python
-    ln -nsf "$BUILD_DIR/.heroku/vendor" /app/.heroku/vendor
-    # Note: .heroku/src is copied in later.
-fi
-
-# Download / Install Python, from pre-build binaries available on Amazon S3.
-# This step also bootstraps pip / setuptools.
-install_python_start_time=$(nowms)
-source "${BUILDPACK_DIR}/bin/steps/python"
-meta_time "python_install_duration" "${install_python_start_time}"
-
-# Install Pipenv dependencies, if a Pipfile was provided.
-source "${BUILDPACK_DIR}/bin/steps/pipenv"
-
-# If no requirements.txt file given, assume `setup.py develop` is intended.
-# This allows for people to ship a setup.py application to Heroku
-
-if [[ ! -f requirements.txt ]] && [[ ! -f Pipfile ]]; then
-  meta_set "setup_py_only" "true"
-  echo "-e ." > requirements.txt
-else
-  meta_set "setup_py_only" "false"
+	# python expects to reside in /app, so set up symlinks
+	# we will not remove these later so subsequent buildpacks can still invoke it
+	ln -nsf "${BUILD_DIR}/.heroku/python" /app/.heroku/python
 fi
 
-# SQLite3 support.
-# This sets up and installs sqlite3 dev headers and the sqlite3 binary but not the
-# libsqlite3-0 library since that exists on the stack image.
-install_sqlite_start_time=$(nowms)
-source "${BUILDPACK_DIR}/bin/steps/sqlite3"
-buildpack_sqlite3_install
-meta_time "sqlite_install_duration" "${install_sqlite_start_time}"
-
-# pip install
-# -----------
-
-# Install dependencies with pip (where the magic happens).
-source "${BUILDPACK_DIR}/bin/steps/pip-install"
+python::install "${BUILD_DIR}" "${STACK}" "${python_full_version}" "${python_major_version}" "${python_version_origin}"
+
+# Install the package manager and related tools.
+package_manager_install_start_time=$(build_data::current_unix_realtime)
+case "${package_manager}" in
+	pip)
+		pip::install_pip "${python_home}" "${python_major_version}" "${EXPORT_PATH}" "${PROFILE_PATH}"
+		;;
+	pipenv)
+		pipenv::install_pipenv "${python_home}" "${python_major_version}" "${EXPORT_PATH}" "${PROFILE_PATH}"
+		;;
+	poetry)
+		poetry::install_poetry "${python_home}" "${python_major_version}" "${CACHE_DIR}" "${EXPORT_PATH}"
+		;;
+	uv)
+		uv::install_uv "${CACHE_DIR}" "${EXPORT_PATH}" "${python_home}"
+		;;
+	*)
+		utils::abort_internal_error "Unhandled package manager: ${package_manager}"
+		;;
+esac
+build_data::set_duration "package_manager_install_duration" "${package_manager_install_start_time}"
+
+# Install app dependencies.
+dependencies_install_start_time=$(build_data::current_unix_realtime)
+case "${package_manager}" in
+	pip)
+		pip::install_dependencies
+		;;
+	pipenv)
+		pipenv::install_dependencies
+		;;
+	poetry)
+		poetry::install_dependencies
+		;;
+	uv)
+		uv::install_dependencies
+		;;
+	*)
+		utils::abort_internal_error "Unhandled package manager: ${package_manager}"
+		;;
+esac
+build_data::set_duration "dependencies_install_duration" "${dependencies_install_start_time}"
 
 # Support for NLTK corpora.
-nltk_downloader_start_time=$(nowms)
-sub_env "${BUILDPACK_DIR}/bin/steps/nltk"
-meta_time "nltk_downloader_duration" "${nltk_downloader_start_time}"
-
-# Support for editable installations. Here, we are copying pip–created src directory,
-# and copying it into the proper place (the logical place to do this was early, but it must be done here).
-# In CI, $BUILD_DIR is /app.
-# Realpath is used to support use-cases where one of the locations is a symlink to the other.
-if [[ "$(realpath "${BUILD_DIR}")" != "$(realpath /app)" ]]; then
-  rm -rf "$BUILD_DIR/.heroku/src"
-  deep-cp /app/.heroku/src "$BUILD_DIR/.heroku/src"
-fi
-
+nltk_downloader_start_time=$(build_data::current_unix_realtime)
+# TODO: Migrate this script to functions under `lib/` and stop running it in a subshell.
+"${BUILDPACK_DIR}/bin/steps/nltk"
+build_data::set_duration "nltk_downloader_duration" "${nltk_downloader_start_time}"
 
 # Django collectstatic support.
 # The buildpack automatically runs collectstatic for Django applications.
-# This is the cause for the majority of build failures on the Python platform.
-# These failures are intentional — if collectstatic (which can be tricky, at times) fails,
-# your build fails.
-collectstatic_start_time=$(nowms)
-sub_env "${BUILDPACK_DIR}/bin/steps/collectstatic"
-meta_time "django_collectstatic_duration" "${collectstatic_start_time}"
-
+collectstatic_start_time=$(build_data::current_unix_realtime)
+# TODO: Migrate this script to functions under `lib/` and stop running it in a subshell.
+"${BUILDPACK_DIR}/bin/steps/collectstatic"
+build_data::set_duration "django_collectstatic_duration" "${collectstatic_start_time}"
 
 # Programmatically create .profile.d script for application runtime environment variables.
 
 # Set the PATH to include Python / pip / pipenv / etc.
-set_env PATH "\$HOME/.heroku/python/bin:\$PATH"
+set_env PATH "\${HOME}/.heroku/python/bin:\${PATH}"
 # Tell Python to run in unbuffered mode.
 set_env PYTHONUNBUFFERED true
 # Tell Python where it lives.
-set_env PYTHONHOME "\$HOME/.heroku/python"
+set_env PYTHONHOME "\${HOME}/.heroku/python"
 # Set variables for C libraries.
-set_env LIBRARY_PATH "\$HOME/.heroku/vendor/lib:\$HOME/.heroku/python/lib:\$LIBRARY_PATH"
-set_env LD_LIBRARY_PATH "\$HOME/.heroku/vendor/lib:\$HOME/.heroku/python/lib:\$LD_LIBRARY_PATH"
+set_env LIBRARY_PATH "\${HOME}/.heroku/python/lib\${LIBRARY_PATH:+:\${LIBRARY_PATH}}"
+set_env LD_LIBRARY_PATH "\${HOME}/.heroku/python/lib\${LD_LIBRARY_PATH:+:\${LD_LIBRARY_PATH}}"
 # Locale.
 set_default_env LANG en_US.UTF-8
-# The Python hash seed is set to random.
-set_default_env PYTHONHASHSEED random
 # Tell Python to look for Python modules in the /app dir. Don't change this.
-set_default_env PYTHONPATH "\$HOME"
+set_default_env PYTHONPATH "\${HOME}"
 
 # Python expects to be in /app, if at runtime, it is not, set
 # up symlinks… this can occur when the subdir buildpack is used.
-cat <<EOT >> "$PROFILE_PATH"
+cat <<EOT >>"${PROFILE_PATH}"
 if [[ \$HOME != "/app" ]]; then
     mkdir -p /app/.heroku
     ln -nsf "\$HOME/.heroku/python" /app/.heroku/python
-    ln -nsf "\$HOME/.heroku/vendor" /app/.heroku/vendor
 fi
 EOT
 
-# At runtime, rewrite paths in editable package .egg-link, .pth and finder files from the build time paths
-# (such as `/tmp/build_<hash>`) back to `/app`. This is not done during the build itself, since later
-# buildpacks still need the build time paths.
+# When dependencies are installed in editable mode, the package manager/build backend creates `.pth`
+# (and related) files in site-packages, which contain absolute path references to the actual location
+# of the packages. By default the Heroku build runs from a directory like `/tmp/build_<hash>`, which
+# changes every build and also differs from the app location at runtime (`/app`). This means any build
+# directory paths referenced in .pth and related files will no longer exist at runtime or during cached
+# rebuilds, unless we rewrite the paths.
+#
+# Ideally, we would be able to rewrite all paths to use the `/app/.heroku/python/` symlink trick we use
+# when invoking Python, since then the same path would work across the current build, runtime and cached
+# rebuilds. However, this trick only works for paths under that directory (since it's not possible to
+# symlink `/app` or other directories we don't own), and when apps use path-based editable dependencies
+# the paths will be outside of that (such as a subdirectory of the app source, or even the root of the
+# build directory). We also can't just rewrite all paths now ready for runtime, since other buildpacks
+# might run after this one that make use of the editable dependencies. As such, we have to perform path
+# rewriting for path-based editable dependencies at app boot instead.
+#
+# For VCS editable dependencies, we can use the symlink trick and so configure the repo checkout location
+# as `/app/.heroku/python/src/`, which in theory should mean the `.pth` files use that path. However,
+# some build backends (such as setuptools' PEP660 implementation) call realpath on it causing the
+# `/tmp/build_*` location to be written instead, meaning VCS src paths need to be rewritten regardless.
+#
+# In addition to ensuring dependencies work for subsequent buildpacks and at runtime, they must also
+# work for cached rebuilds. Most package managers will reinstall editable dependencies regardless on
+# the next install, which means we can avoid having to rewrite paths on cache restore from the old build
+# directory to the new location (`/tmp/build_<different-hash>`). However, Pipenv has a bug when using
+# PEP660 style editable VCS dependencies where it won't reinstall if it's missing (or in our case, the
+# path has changed), which means we must make sure that VCS src paths stored in the cache do use the
+# symlink path. See: https://github.com/pypa/pipenv/issues/6348
+#
+# As such, we have to perform two rewrites:
+# 1. At build time, of just the VCS editable paths (which we can safely change to /app paths early).
+# 2. At runtime, to rewrite the remaining path-based editable dependency paths.
 if [[ "${BUILD_DIR}" != "/app" ]]; then
-  cat <<EOT >> "$PROFILE_PATH"
-find .heroku/python/lib/python*/site-packages/ -type f -and \( -name '*.egg-link' -or -name '*.pth' -or -name '__editable___*_finder.py' \) -exec sed -i -e 's#${BUILD_DIR}#/app#' {} \+
-EOT
+	find .heroku/python/lib/python*/site-packages/ -type f -and \( -name '*.egg-link' -or -name '*.pth' -or -name '__editable___*_finder.py' \) -exec sed -i -e "s#${BUILD_DIR}/.heroku/python#/app/.heroku/python#" {} \+
+	cat <<-EOT >>"${PROFILE_PATH}"
+		find .heroku/python/lib/python*/site-packages/ -type f -and \( -name '*.egg-link' -or -name '*.pth' -or -name '__editable___*_finder.py' \) -exec sed -i -e 's#${BUILD_DIR}#/app#' {} \+
+	EOT
 fi
 
 # Install sane-default script for $WEB_CONCURRENCY and $FORWARDED_ALLOW_IPS.
-cp "${BUILDPACK_DIR}/vendor/WEB_CONCURRENCY.sh" "$WEB_CONCURRENCY_PROFILE_PATH"
-cp "${BUILDPACK_DIR}/vendor/python.gunicorn.sh" "$GUNICORN_PROFILE_PATH"
-
-# Experimental post_compile hook. Don't remove this.
-source "${BUILDPACK_DIR}/bin/steps/hooks/post_compile"
-
-# Store new artifacts in the cache.
-rm -rf "$CACHE_DIR/.heroku/python"
-rm -rf "$CACHE_DIR/.heroku/python-version"
-rm -rf "$CACHE_DIR/.heroku/python-stack"
-rm -rf "$CACHE_DIR/.heroku/vendor"
-rm -rf "$CACHE_DIR/.heroku/src"
-
-mkdir -p "$CACHE_DIR/.heroku"
-cp -R .heroku/python "$CACHE_DIR/.heroku/"
-cp -R .heroku/python-version "$CACHE_DIR/.heroku/"
-cp -R .heroku/python-stack "$CACHE_DIR/.heroku/" &> /dev/null || true
-if [[ -d .heroku/src ]]; then
-  cp -R .heroku/src "$CACHE_DIR/.heroku/" &> /dev/null || true
+cp "${BUILDPACK_DIR}/vendor/WEB_CONCURRENCY.sh" "${WEB_CONCURRENCY_PROFILE_PATH}"
+cp "${BUILDPACK_DIR}/vendor/python.gunicorn.sh" "${GUNICORN_PROFILE_PATH}"
+
+# Runs a `bin/post_compile` script if found in the app source, allowing build customisation.
+hooks::run_hook "post_compile"
+
+cache::save "${BUILD_DIR}" "${CACHE_DIR}" "${STACK}" "${python_full_version}" "${package_manager}"
+
+if [[ "${package_manager}" != "uv" ]]; then
+	output::notice <<-EOF
+		Note: We recently added support for the package manager uv:
+		https://devcenter.heroku.com/changelog-items/3238
+
+		It's now our recommended Python package manager, since it
+		supports lockfiles, is faster, gives more helpful error
+		messages, and is actively maintained by a full-time team.
+
+		If you haven't tried it yet, we suggest you take a look!
+		https://docs.astral.sh/uv/
+	EOF
 fi
 
-meta_time "total_duration" "${compile_start_time}"
+build_data::set_duration "total_duration" "${compile_start_time}"
diff --git a/bin/default_pythons b/bin/default_pythons
deleted file mode 100755
index 04caa85d7..000000000
--- a/bin/default_pythons
+++ /dev/null
@@ -1,19 +0,0 @@
-#!/usr/bin/env bash
-
-# Disable unused env var warning, since shellcheck doesn't take into account
-# that this file is sourced. We don't want to use export since it exposes
-# the env vars to subprocesses.
-# shellcheck disable=2034
-
-LATEST_312="python-3.12.4"
-LATEST_311="python-3.11.9"
-LATEST_310="python-3.10.14"
-LATEST_39="python-3.9.19"
-LATEST_38="python-3.8.19"
-# TODO: Remove these EOL versions once pipenv-python-version is refactored.
-LATEST_37="python-3.7.17"
-LATEST_36="python-3.6.15"
-LATEST_35="python-3.5.10"
-LATEST_34="python-3.4.10"
-LATEST_27="python-2.7.18"
-DEFAULT_PYTHON_VERSION="${LATEST_312}"
diff --git a/bin/detect b/bin/detect
index d7b27069f..86da2ddc0 100755
--- a/bin/detect
+++ b/bin/detect
@@ -1,11 +1,17 @@
 #!/usr/bin/env bash
-# Usage: bin/compile <build-dir>
+# Usage: bin/detect <build-dir>
 # See: https://devcenter.heroku.com/articles/buildpack-api
 
 set -euo pipefail
+shopt -s inherit_errexit
 
 BUILD_DIR="${1}"
 
+# The absolute path to the root of the buildpack.
+BUILDPACK_DIR=$(cd "$(dirname "$(dirname "${BASH_SOURCE[0]}")")" && pwd)
+
+source "${BUILDPACK_DIR}/lib/output.sh"
+
 # Filenames that if found in a project mean it should be treated as a Python project,
 # and so pass this buildpack's detection phase.
 #
@@ -13,57 +19,78 @@ BUILD_DIR="${1}"
 # so that Python projects that are missing some of the required files still pass detection,
 # allowing us to show a helpful error message during the build phase.
 KNOWN_PYTHON_PROJECT_FILES=(
-  .python-version
-  app.py
-  main.py
-  manage.py
-  pdm.lock
-  Pipfile
-  Pipfile.lock
-  poetry.lock
-  pyproject.toml
-  requirements.txt
-  runtime.txt
-  setup.cfg
-  setup.py
-  uv.lock
+	.python-version
+	__init__.py
+	app.py
+	main.py
+	manage.py
+	pdm.lock
+	Pipfile
+	Pipfile.lock
+	poetry.lock
+	pyproject.toml
+	requirements.txt
+	runtime.txt
+	server.py
+	setup.cfg
+	setup.py
+	uv.lock
+	# Commonly seen misspellings of requirements.txt. (Which occur since pip doesn't
+	# create/manage requirements files itself, so the filenames are manually typed.)
+	requeriments.txt
+	requirement.txt
+	requirements
+	requirements.text
+	Requirements.txt
+	requirements.txt.txt
+	requirments.txt
+	# Whilst the pyc cache and virtual environments shouldn't be committed to Git (and so
+	# shouldn't normally be present during the build), they are often present for beginner
+	# Python apps that are missing all of the other Python related files above.
+	__pycache__/
+	.venv/
+	venv/
 )
 
-for filename in "${KNOWN_PYTHON_PROJECT_FILES[@]}"; do
-  if [[ -f "${BUILD_DIR}/${filename}" ]]; then
-    echo "Python"
-    exit 0
-  fi
+for filepath in "${KNOWN_PYTHON_PROJECT_FILES[@]}"; do
+	# Using -e since we need to check for both files and directories.
+	if [[ -e "${BUILD_DIR}/${filepath}" ]]; then
+		echo "Python"
+		exit 0
+	fi
 done
 
-# Cytokine incorrectly indents the first line, so we have to leave it empty.
-echo 1>&2
-
 # Note: This error message intentionally doesn't list all of the filetypes above,
 # since during compile the build will still require a package manager file, so it
-# makes sense to describe the stricter requirements up front.
-# TODO: Overhaul logging helpers so they can handle prefixing multi-line strings, and switch to them.
-sed 's/^/ !     /' 1>&2 << EOF
+# makes sense to describe the stricter requirements upfront.
+output::error <<EOF
 Error: Your app is configured to use the Python buildpack,
 but we couldn't find any supported Python project files.
 
-A Python app on Heroku must have either a 'requirements.txt' or
-'Pipfile' package manager file in the root directory of its
-source code.
+A Python app on Heroku must have either a 'requirements.txt',
+'Pipfile.lock', 'poetry.lock' or 'uv.lock' package manager file
+in the root directory of its source code.
 
 Currently the root directory of your app contains:
 
-$(ls -1 --indicator-style=slash "${BUILD_DIR}")
+$(ls -1A --indicator-style=slash "${BUILD_DIR}" || true)
 
 If your app already has a package manager file, check that it:
 
 1. Is in the top level directory (not a subdirectory).
 2. Has the correct spelling (the filenames are case-sensitive).
 3. Isn't listed in '.gitignore' or '.slugignore'.
+4. Has been added to the Git repository using 'git add --all'
+   and then committed using 'git commit'.
 
 Otherwise, add a package manager file to your app. If your app has
 no dependencies, then create an empty 'requirements.txt' file.
 
+If you aren't sure which package manager to use, we recommend
+trying uv, since it supports lockfiles, is extremely fast, and
+is actively maintained by a full-time team:
+https://docs.astral.sh/uv/
+
 For help with using Python on Heroku, see:
 https://devcenter.heroku.com/articles/getting-started-with-python
 https://devcenter.heroku.com/articles/python-support
diff --git a/bin/release b/bin/release
index 282d26e44..af46b035d 100755
--- a/bin/release
+++ b/bin/release
@@ -3,6 +3,7 @@
 # See: https://devcenter.heroku.com/articles/buildpack-api
 
 set -euo pipefail
+shopt -s inherit_errexit
 
 BUILD_DIR="${1}"
 
@@ -12,19 +13,16 @@ BUILDPACK_DIR=$(cd "$(dirname "$(dirname "${BASH_SOURCE[0]}")")" && pwd)
 # Unfortunately the build system doesn't source the `export` script before
 # running `bin/release`, so we have to do so manually to ensure the buildpack
 # Python is used by `is_module_available` instead of system Python.
-# We also have to disable Bash error on undefined variables, since not all env
-# vars used in the export script will be set by default (eg `LIBRARY_PATH`).
-set +u
 # shellcheck source=/dev/null
 source "${BUILDPACK_DIR}/export"
-set -u
 
 source "${BUILDPACK_DIR}/bin/utils"
 
+# shellcheck disable=SC2310 # TODO: This function is invoked in an '&&' condition so set -e will be disabled.
 if [[ -f "${BUILD_DIR}/manage.py" ]] && is_module_available 'django' && is_module_available 'psycopg2'; then
-cat <<EOF
----
-addons:
-  - heroku-postgresql
-EOF
+	cat <<-'EOF'
+		---
+		addons:
+		  - heroku-postgresql
+	EOF
 fi
diff --git a/bin/report b/bin/report
index f88b2b604..f73f96c68 100755
--- a/bin/report
+++ b/bin/report
@@ -1,117 +1,28 @@
 #!/usr/bin/env bash
 # Usage: bin/report <build-dir> <cache-dir> <env-dir>
 
-# Produces a build report containing metadata about the build, that's consumed by the build system.
-# This script is run for both successful and failing builds, so it should not assume the build ran
-# to completion (e.g. Python or other tools may not even have been installed).
+# Produces a build report emitted to stdout, containing metadata about the build, that's
+# consumed by the build system. See the pip_spec.rb for an example build report payload.
 #
-# Metadata must be emitted to stdout as valid YAML key-value pairs. Any fields that should always
-# be typed as a string must be explicitly quoted.
-#
-# Example valid stdout:
-#   python_version: 'X.Y.Z'
-#   python_install_duration: 1.234
+# This script is run for both successful and failing builds, so it should not assume the
+# build ran to completion (e.g. Python or other tools may not even have been installed).
 #
 # Failures in this script don't cause the overall build to fail (and won't appear in user
 # facing build logs) to avoid breaking builds unnecessarily / causing confusion. To debug
 # issues check the internal build system logs for `buildpack.report.failed` events, or
-# when developing run `make compile` in this repo locally, which runs `bin/report` too.
+# when developing run `make run` in this repo locally, which runs `bin/report` too.
+#
+# Note: The build system doesn't source the `export` script before running this script,
+# so Python/the package manager won't be on PATH by default.
 
 set -euo pipefail
+shopt -s inherit_errexit
 
 CACHE_DIR="${2}"
 
 # The absolute path to the root of the buildpack.
 BUILDPACK_DIR=$(cd "$(dirname "$(dirname "${BASH_SOURCE[0]}")")" && pwd)
 
-# The build system doesn't source the `export` script before running this script, so we have to do
-# so manually (if it exists) so that buildpack Python/Pip can be found (if the build succeeded).
-# We have to disable Bash error on undefined variables for now, since not all env vars used in the
-# export script will be set by default (eg `LIBRARY_PATH`).
-EXPORT_FILE="${BUILDPACK_DIR}/export"
-if [[ -f "${EXPORT_FILE}" ]]; then
-  set +u
-  # shellcheck source=/dev/null
-  source "${EXPORT_FILE}"
-  set -u
-fi
-
-source "${BUILDPACK_DIR}/lib/metadata.sh"
-meta_init "${CACHE_DIR}" "python"
-
-# Emit the key / value pair unquoted to stdout. Skips if the value is empty.
-# Based on: https://github.com/heroku/heroku-buildpack-nodejs/blob/main/bin/report
-kv_pair() {
-  local key="${1}"
-  local value="${2}"
-  if [[ -n "${value}" ]]; then
-    echo "${key}: ${value}"
-  fi
-}
-
-# Emit the key / value pair to stdout, safely quoting the string. Skips if the value is empty.
-# Based on: https://github.com/heroku/heroku-buildpack-nodejs/blob/main/bin/report
-# (Though instead uses single quotes instead of double to avoid escaping issues.)
-kv_pair_string() {
-  local key="${1}"
-  local value="${2}"
-  if [[ -n "${value}" ]]; then
-    # Escape any existing single quotes, which for YAML means replacing `'` with `''`.
-    value="${value//\'/\'\'}"
-    echo "${key}: '${value}'"
-  fi
-}
-
-STRING_FIELDS=(
-  django_collectstatic
-  failure_reason
-  nltk_downloader
-  package_manager
-  pip_version
-  pipenv_version
-  python_version_major
-  python_version_reason
-  python_version
-  setuptools_version
-  wheel_version
-)
-
-# We don't want to quote numeric or boolean fields.
-ALL_OTHER_FIELDS=(
-  dependencies_install_duration
-  django_collectstatic_duration
-  nltk_downloader_duration
-  pipenv_has_lockfile
-  post_compile_hook
-  post_compile_hook_duration
-  pre_compile_hook
-  pre_compile_hook_duration
-  python_install_duration
-  setup_py_only
-  sqlite_install_duration
-  total_duration
-)
-
-for field in "${STRING_FIELDS[@]}"; do
-  kv_pair_string "${field}" "$(meta_get "${field}")"
-done
-
-for field in "${ALL_OTHER_FIELDS[@]}"; do
-  kv_pair "${field}" "$(meta_get "${field}")"
-done
-
-# If the build failed, pip might not have been installed yet.
-if command -v pip >/dev/null; then
-  # Determine pysqlite3 usage since it's the only package that requires the sqlite3 headers.
-  if pip show pysqlite3 &>/dev/null; then
-    kv_pair pysqlite3_installed true
-  else
-    kv_pair pysqlite3_installed false
-  fi
+source "${BUILDPACK_DIR}/lib/build_data.sh"
 
-  if pip show pysqlite3-binary &>/dev/null; then
-    kv_pair pysqlite3_binary_installed true
-  else
-    kv_pair pysqlite3_binary_installed false
-  fi
-fi
+build_data::print_bin_report_json
diff --git a/bin/steps/collectstatic b/bin/steps/collectstatic
index 5731408a4..0abed5a56 100755
--- a/bin/steps/collectstatic
+++ b/bin/steps/collectstatic
@@ -4,39 +4,48 @@
 # automatically be executed as part of the build process. If collectstatic
 # fails, your build fails.
 
-# This functionality will only activate if Django is in requirements.txt.
+# This functionality will only activate if Django is installed.
 
 # Runtime arguments:
 #   - $DISABLE_COLLECTSTATIC: disables this functionality.
 #   - $DEBUG_COLLECTSTATIC: upon failure, print out environment variables.
 
-# This script is run in a subshell via sub_env so doesn't inherit the options/vars/utils from `bin/compile`.
-# TODO: Stop running this script in a subshell.
-set -eo pipefail
+# This script is run in a subshell so doesn't inherit the options/vars/utils from `bin/compile`.
+# TODO: Migrate this script to functions under `lib/` and stop running the entire script in a subshell,
+# and instead only the parts that need the user-provided config vars loaded.
+set -euo pipefail
 BUILDPACK_DIR=$(cd "$(dirname "$(dirname "$(dirname "${BASH_SOURCE[0]}")")")" && pwd)
 source "${BUILDPACK_DIR}/bin/utils"
+source "${BUILDPACK_DIR}/lib/build_data.sh"
+source "${BUILDPACK_DIR}/lib/output.sh"
 
-# Required for `meta_set`.
-source "${BUILDPACK_DIR}/lib/metadata.sh"
-# shellcheck disable=SC2153
-meta_init "${CACHE_DIR}" "python"
+# This must be after the imports above, to prevent user-provided config vars from overwriting
+# env vars used by the buildpack such as `CACHE_DIR`:
+# https://github.com/heroku/heroku-buildpack-python/issues/972
+# TODO: Reduce the scope of this even further, as part of refactoring this file.
+export_env "${ENV_DIR}"
 
 if [[ -f .heroku/collectstatic_disabled ]]; then
-  puts-step "Skipping Django collectstatic since the file '.heroku/collectstatic_disabled' exists."
-  puts-warn "This approach is deprecated, please set the env var DISABLE_COLLECTSTATIC=1 instead."
-  meta_set "django_collectstatic" "disabled-file"
-  exit 0
+	output::step "Skipping Django collectstatic since the file '.heroku/collectstatic_disabled' exists."
+	output::warning <<-'EOF'
+		Warning: The .heroku/collectstatic_disabled file is deprecated.
+
+		Please remove the file and set the env var DISABLE_COLLECTSTATIC=1 instead.
+	EOF
+	build_data::set_string "django_collectstatic" "disabled-file"
+	exit 0
 fi
 
 if [[ "${DISABLE_COLLECTSTATIC:-0}" != "0" ]]; then
-  puts-step "Skipping Django collectstatic since the env var DISABLE_COLLECTSTATIC is set."
-  meta_set "django_collectstatic" "disabled-env-var"
-  exit 0
+	output::step "Skipping Django collectstatic since the env var DISABLE_COLLECTSTATIC is set."
+	build_data::set_string "django_collectstatic" "disabled-env-var"
+	exit 0
 fi
 
 # Ensure that Django is actually installed.
+# shellcheck disable=SC2310 # TODO: This function is invoked in an 'if' condition so set -e will be disabled.
 if ! is_module_available 'django'; then
-  exit 0
+	exit 0
 fi
 
 # Location of 'manage.py', if it exists.
@@ -44,59 +53,66 @@ MANAGE_FILE=$(find . -maxdepth 3 -type f -name 'manage.py' -printf '%d\t%P\n' |
 MANAGE_FILE=${MANAGE_FILE:-fakepath}
 
 if [[ ! -f "${MANAGE_FILE}" ]]; then
-  puts-step "Skipping Django collectstatic since no manage.py file found."
-  meta_set "django_collectstatic" "skipped-no-manage-py"
-  exit 0
+	output::step "Skipping Django collectstatic since no manage.py file found."
+	build_data::set_string "django_collectstatic" "skipped-no-manage-py"
+	exit 0
 fi
 
-meta_set "django_collectstatic" "enabled"
+build_data::set_string "django_collectstatic" "enabled"
 
-puts-step "$ python $MANAGE_FILE collectstatic --noinput"
+output::step "$ python ${MANAGE_FILE} collectstatic --noinput"
 
-PYTHONPATH=${PYTHONPATH:-.}
+PYTHONPATH="${PYTHONPATH:-.}"
 export PYTHONPATH
 COLLECTSTATIC_LOG=$(mktemp)
 
 set +e
-python "$MANAGE_FILE" collectstatic --noinput --traceback 2>&1 | tee "$COLLECTSTATIC_LOG" | sed '/^Post-processed/d;/^Copying/d;/^$/d' | indent
+python "${MANAGE_FILE}" collectstatic --noinput --traceback |& tee "${COLLECTSTATIC_LOG}" |& output::indent
 COLLECTSTATIC_STATUS="${PIPESTATUS[0]}"
 set -e
 
 echo
 
 if [[ "${COLLECTSTATIC_STATUS}" == 0 ]]; then
-  exit 0
+	exit 0
 fi
 
 # Display a warning if collectstatic failed.
-if grep -q 'SyntaxError' "$COLLECTSTATIC_LOG"; then
-  meta_set "failure_reason" "collectstatic-syntax-error"
-elif grep -q 'ImproperlyConfigured' "$COLLECTSTATIC_LOG"; then
-  meta_set "failure_reason" "collectstatic-improper-configuration"
-elif grep -q 'The CSS file' "$COLLECTSTATIC_LOG"; then
-  meta_set "failure_reason" "collectstatic-fancy-references"
-elif grep -q 'OSError' "$COLLECTSTATIC_LOG"; then
-  meta_set "failure_reason" "collectstatic-missing-file"
+if grep -q 'SyntaxError' "${COLLECTSTATIC_LOG}"; then
+	build_data::set_string "failure_reason" "collectstatic-syntax-error"
+elif grep -q 'ImproperlyConfigured' "${COLLECTSTATIC_LOG}"; then
+	build_data::set_string "failure_reason" "collectstatic-improper-configuration"
+elif grep -q 'The CSS file' "${COLLECTSTATIC_LOG}"; then
+	build_data::set_string "failure_reason" "collectstatic-fancy-references"
+elif grep -q 'OSError' "${COLLECTSTATIC_LOG}"; then
+	build_data::set_string "failure_reason" "collectstatic-missing-file"
 else
-  meta_set "failure_reason" "collectstatic-other"
+	build_data::set_string "failure_reason" "collectstatic-other"
 fi
 
-echo " !     Error while running '$ python $MANAGE_FILE collectstatic --noinput'."
-echo "       See traceback above for details."
-echo
-echo "       You may need to update application code to resolve this error."
-echo "       Or, you can disable collectstatic for this application:"
-echo
-echo "          $ heroku config:set DISABLE_COLLECTSTATIC=1"
-echo
-echo "       https://devcenter.heroku.com/articles/django-assets"
+output::error <<-EOF
+	Error: Unable to generate Django static files.
+
+	The 'python ${MANAGE_FILE} collectstatic --noinput' Django
+	management command to generate static files failed.
+
+	See the traceback above for details.
+
+	You may need to update application code to resolve this error.
+	Or, you can disable collectstatic for this application:
+
+	   $ heroku config:set DISABLE_COLLECTSTATIC=1
+
+	https://devcenter.heroku.com/articles/django-assets
+EOF
 
 # Additionally, dump out the environment, if debug mode is on.
-if [[ -n "$DEBUG_COLLECTSTATIC" ]]; then
-  echo
-  echo "****** Collectstatic environment variables:"
-  echo
-  env | indent
+if [[ "${DEBUG_COLLECTSTATIC:-0}" == "1" ]]; then
+	echo
+	echo "****** Collectstatic environment variables:"
+	echo
+	# TODO: Sort the displayed env vars to make the order deterministic.
+	env | output::indent
 fi
 
 exit 1
diff --git a/bin/steps/hooks/post_compile b/bin/steps/hooks/post_compile
deleted file mode 100755
index 111491ee7..000000000
--- a/bin/steps/hooks/post_compile
+++ /dev/null
@@ -1,12 +0,0 @@
-#!/usr/bin/env bash
-
-if [[ -f bin/post_compile ]]; then
-    post_compile_hook_start_time=$(nowms)
-    meta_set "post_compile_hook" "true"
-    echo "-----> Running post-compile hook"
-    chmod +x bin/post_compile
-    sub_env bin/post_compile
-    meta_time "post_compile_hook_duration" "${post_compile_hook_start_time}"
-else
-    meta_set "post_compile_hook" "false"
-fi
diff --git a/bin/steps/hooks/pre_compile b/bin/steps/hooks/pre_compile
deleted file mode 100755
index c22eb1102..000000000
--- a/bin/steps/hooks/pre_compile
+++ /dev/null
@@ -1,12 +0,0 @@
-#!/usr/bin/env bash
-
-if [[ -f bin/pre_compile ]]; then
-    pre_compile_hook_start_time=$(nowms)
-    meta_set "pre_compile_hook" "true"
-    echo "-----> Running pre-compile hook"
-    chmod +x bin/pre_compile
-    sub_env bin/pre_compile
-    meta_time "pre_compile_hook_duration" "${pre_compile_hook_start_time}"
-else
-    meta_set "pre_compile_hook" "false"
-fi
diff --git a/bin/steps/nltk b/bin/steps/nltk
index f04e60cde..67040d103 100755
--- a/bin/steps/nltk
+++ b/bin/steps/nltk
@@ -1,38 +1,52 @@
 #!/usr/bin/env bash
 
-# This script is run in a subshell via sub_env so doesn't inherit the options/vars/utils from `bin/compile`.
-# TODO: Stop running this script in a subshell.
-set -eo pipefail
+# This script is run in a subshell so doesn't inherit the options/vars/utils from `bin/compile`.
+# TODO: Migrate this script to functions under `lib/` and stop running the entire script in a subshell.
+set -euo pipefail
 BUILDPACK_DIR=$(cd "$(dirname "$(dirname "$(dirname "${BASH_SOURCE[0]}")")")" && pwd)
 source "${BUILDPACK_DIR}/bin/utils"
-
-# Required for `meta_set`.
-source "${BUILDPACK_DIR}/lib/metadata.sh"
-# shellcheck disable=SC2153
-meta_init "${CACHE_DIR}" "python"
+source "${BUILDPACK_DIR}/lib/build_data.sh"
+source "${BUILDPACK_DIR}/lib/output.sh"
 
 # These are required by `set_env`.
-PROFILE_PATH="${BUILD_DIR}/.profile.d/python.sh"
+PROFILE_PATH="${BUILD_DIR:?}/.profile.d/python.sh"
 EXPORT_PATH="${BUILDPACK_DIR}/export"
 
 # Check that nltk was installed by pip, otherwise obviously not needed
+# shellcheck disable=SC2310 # TODO: This function is invoked in an 'if' condition so set -e will be disabled.
 if is_module_available 'nltk'; then
-    puts-step "Downloading NLTK corpora..."
-
-    nltk_packages_definition="$BUILD_DIR/nltk.txt"
-
-    if [[ -f "$nltk_packages_definition" ]]; then
-        meta_set "nltk_downloader" "enabled"
-
-        readarray -t nltk_packages < "$nltk_packages_definition"
-        puts-step "Downloading NLTK packages: ${nltk_packages[*]}"
-
-        python -m nltk.downloader -d "$BUILD_DIR/.heroku/python/nltk_data" "${nltk_packages[@]}" | indent
-        set_env NLTK_DATA "/app/.heroku/python/nltk_data"
-
-    else
-        meta_set "nltk_downloader" "skipped-no-nltk-file"
-        puts-warn "'nltk.txt' not found, not downloading any corpora"
-        puts-warn "Learn more: https://devcenter.heroku.com/articles/python-nltk"
-    fi
+	output::step "Downloading NLTK corpora..."
+
+	nltk_packages_definition="${BUILD_DIR}/nltk.txt"
+
+	if [[ -f "${nltk_packages_definition}" ]]; then
+		build_data::set_string "nltk_downloader" "enabled"
+
+		readarray -t nltk_packages <"${nltk_packages_definition}"
+		output::step "Downloading NLTK packages: ${nltk_packages[*]}"
+
+		# Note: We have to use the raw build directory path here and not the symlinked `/app` path,
+		# otherwise it will cause a false positive in NLTK v3.9.3's new Zip Slip security check,
+		# which doesn't handle symlinked paths correctly: https://github.com/nltk/nltk/issues/3509
+		# TODO: Does this even need user-provided env vars, or can we remove the sub_env usage here?
+		if ! sub_env python -m nltk.downloader -d "${BUILD_DIR}/.heroku/python/nltk_data" "${nltk_packages[@]}" |& output::indent; then
+			output::error <<-EOF
+				Error: Unable to download NLTK data.
+
+				The 'python -m nltk.downloader' command to download NLTK
+				data didn't exit successfully.
+
+				See the log output above for more information.
+			EOF
+			build_data::set_string "failure_reason" "nltk-downloader"
+			exit 1
+		fi
+
+		# Since this will be used at runtime, we must use the symlinked `/app` path and not
+		# the raw build directory path.
+		set_env NLTK_DATA "/app/.heroku/python/nltk_data"
+	else
+		build_data::set_string "nltk_downloader" "skipped-no-nltk-file"
+		echo "       'nltk.txt' not found, not downloading any corpora"
+	fi
 fi
diff --git a/bin/steps/pip-install b/bin/steps/pip-install
deleted file mode 100755
index e180e649d..000000000
--- a/bin/steps/pip-install
+++ /dev/null
@@ -1,44 +0,0 @@
-#!/usr/bin/env bash
-
-if [[ -z "$SKIP_PIP_INSTALL" ]]; then
-    pip_install_start_time=$(nowms)
-    meta_set "package_manager" "pip"
-
-    puts-step "Installing requirements with pip"
-
-    # Set Pip env vars
-    # This reads certain environment variables set on the Heroku app config
-    # and makes them accessible to the pip install process.
-    #
-    # PIP_EXTRA_INDEX_URL allows for an alternate pypi URL to be used.
-    if [[ -r "$ENV_DIR/PIP_EXTRA_INDEX_URL" ]]; then
-        PIP_EXTRA_INDEX_URL="$(cat "$ENV_DIR/PIP_EXTRA_INDEX_URL")"
-        export PIP_EXTRA_INDEX_URL
-    fi
-
-    set +e
-
-    /app/.heroku/python/bin/pip install -r requirements.txt --exists-action=w --src='/app/.heroku/src' --disable-pip-version-check --no-cache-dir --progress-bar off 2>&1 | tee "$WARNINGS_LOG" | cleanup | indent
-    PIP_STATUS="${PIPESTATUS[0]}"
-    set -e
-
-    show-warnings
-
-    if [[ ! $PIP_STATUS -eq 0 ]]; then
-        meta_set "failure_reason" "pip-install"
-        exit 1
-    fi
-
-    cp requirements.txt .heroku/python/requirements-declared.txt
-    /app/.heroku/python/bin/pip freeze --disable-pip-version-check > .heroku/python/requirements-installed.txt
-
-    # Install test dependencies, for CI.
-    if [[ -n "$INSTALL_TEST" ]]; then
-        if [[ -f requirements-test.txt ]]; then
-            puts-step "Installing test dependencies..."
-            /app/.heroku/python/bin/pip install -r requirements-test.txt --exists-action=w --src='/app/.heroku/src' --disable-pip-version-check --no-cache-dir 2>&1 | cleanup | indent
-        fi
-    fi
-
-    meta_time "dependencies_install_duration" "${pip_install_start_time}"
-fi
diff --git a/bin/steps/pipenv b/bin/steps/pipenv
deleted file mode 100755
index d7a190b4b..000000000
--- a/bin/steps/pipenv
+++ /dev/null
@@ -1,55 +0,0 @@
-#!/usr/bin/env bash
-
-# export CLINT_FORCE_COLOR=1
-# export PIPENV_FORCE_COLOR=1
-
-# Previous versions of the buildpack used to cache the checksum of the lockfile to allow
-# for skipping pipenv install if the lockfile was unchanged. However, this is not always safe
-# to do (the lockfile can refer to dependencies that can change independently of the lockfile,
-# for example, when using a local non-editable file dependency), so we no longer ever skip
-# install, and instead defer to pipenv to determine whether install is actually a no-op.
-rm -f .heroku/python/Pipfile.lock.sha256
-
-if [[ -f Pipfile ]]; then
-    pipenv_install_start_time=$(nowms)
-    meta_set "package_manager" "pipenv"
-
-    # Skip installing dependencies using pip later.
-    export SKIP_PIP_INSTALL=1
-
-    # Set Pip env vars
-    # This reads certain environment variables set on the Heroku app config
-    # and makes them accessible to the pip install process.
-    #
-    # PIP_EXTRA_INDEX_URL allows for an alternate pypi URL to be used.
-    if [[ -r "$ENV_DIR/PIP_EXTRA_INDEX_URL" ]]; then
-        PIP_EXTRA_INDEX_URL="$(cat "$ENV_DIR/PIP_EXTRA_INDEX_URL")"
-        export PIP_EXTRA_INDEX_URL
-    fi
-
-    PIPENV_VERSION=$(get_requirement_version 'pipenv')
-    meta_set "pipenv_version" "${PIPENV_VERSION}"
-
-    /app/.heroku/python/bin/pip install --quiet --disable-pip-version-check --no-cache-dir "pipenv==${PIPENV_VERSION}"
-
-    # Install the test dependencies, for CI.
-    # TODO: This is currently inconsistent with the non-test path, since it assumes (but doesn't check for) a lockfile.
-    if [[ -n "$INSTALL_TEST" ]]; then
-        meta_set "pipenv_has_lockfile" "true"
-        puts-step "Installing test dependencies"
-        /app/.heroku/python/bin/pipenv install --dev --system --deploy --extra-pip-args='--src=/app/.heroku/src' 2>&1 | cleanup | indent
-
-    # Install the dependencies.
-    elif [[ ! -f Pipfile.lock ]]; then
-        meta_set "pipenv_has_lockfile" "false"
-        puts-step "Installing dependencies with Pipenv ${PIPENV_VERSION}"
-        /app/.heroku/python/bin/pipenv install --system --skip-lock --extra-pip-args='--src=/app/.heroku/src' 2>&1 | indent
-
-    else
-        meta_set "pipenv_has_lockfile" "true"
-        puts-step "Installing dependencies with Pipenv ${PIPENV_VERSION}"
-        /app/.heroku/python/bin/pipenv install --system --deploy --extra-pip-args='--src=/app/.heroku/src' 2>&1 | indent
-    fi
-
-    meta_time "dependencies_install_duration" "${pipenv_install_start_time}"
-fi
diff --git a/bin/steps/pipenv-python-version b/bin/steps/pipenv-python-version
deleted file mode 100755
index 9adba9002..000000000
--- a/bin/steps/pipenv-python-version
+++ /dev/null
@@ -1,63 +0,0 @@
-#!/usr/bin/env bash
-
-# Detect Python-version with Pipenv.
-
-if [[ -f $BUILD_DIR/Pipfile ]]; then
-
-    if [[ ! -f $BUILD_DIR/runtime.txt ]]; then
-        if [[ ! -f $BUILD_DIR/Pipfile.lock ]]; then
-            puts-warn "No 'Pipfile.lock' found! We recommend you commit this into your repository."
-        fi
-        if [[ -f $BUILD_DIR/Pipfile.lock ]]; then
-            # Ignore unused env var warning since this is used by bin/compile.
-            # shellcheck disable=2034
-            PYTHON_VERSION_SOURCE='Pipfile.lock'
-            set +e
-            PYTHON=$(jq -r '._meta.requires.python_full_version' "$BUILD_DIR/Pipfile.lock")
-            if [[ "$PYTHON" != "null" ]]; then
-                echo "python-$PYTHON" > "$BUILD_DIR/runtime.txt"
-            fi
-            set -e
-
-            if [[ "$PYTHON" == "null" ]]; then
-                PYTHON=$(jq -r '._meta.requires.python_version' "$BUILD_DIR/Pipfile.lock")
-                case "${PYTHON}" in
-                    2.7)
-                        echo "${LATEST_27}" > "${BUILD_DIR}/runtime.txt"
-                        ;;
-                    3.4)
-                        echo "${LATEST_34}" > "${BUILD_DIR}/runtime.txt"
-                        ;;
-                    3.5)
-                        echo "${LATEST_35}" > "${BUILD_DIR}/runtime.txt"
-                        ;;
-                    3.6)
-                        echo "${LATEST_36}" > "${BUILD_DIR}/runtime.txt"
-                        ;;
-                    3.7)
-                        echo "${LATEST_37}" > "${BUILD_DIR}/runtime.txt"
-                        ;;
-                    3.8)
-                        echo "${LATEST_38}" > "${BUILD_DIR}/runtime.txt"
-                        ;;
-                    3.9)
-                        echo "${LATEST_39}" > "${BUILD_DIR}/runtime.txt"
-                        ;;
-                    3.10)
-                        echo "${LATEST_310}" > "${BUILD_DIR}/runtime.txt"
-                        ;;
-                    3.11)
-                        echo "${LATEST_311}" > "${BUILD_DIR}/runtime.txt"
-                        ;;
-                    3.12)
-                        echo "${LATEST_312}" > "${BUILD_DIR}/runtime.txt"
-                        ;;
-                    # TODO: Make this case an error
-                    *) ;;
-                esac
-            fi
-
-
-        fi
-    fi
-fi
diff --git a/bin/steps/python b/bin/steps/python
deleted file mode 100755
index 333a9302a..000000000
--- a/bin/steps/python
+++ /dev/null
@@ -1,197 +0,0 @@
-#!/usr/bin/env bash
-
-PYTHON_VERSION=$(cat runtime.txt)
-# Remove leading and trailing whitespace. Note: This implementation relies upon
-# `extglob` being set, which is the case thanks to `bin/utils` being run earlier.
-PYTHON_VERSION="${PYTHON_VERSION##+([[:space:]])}"
-PYTHON_VERSION="${PYTHON_VERSION%%+([[:space:]])}"
-
-function eol_python_version_error() {
-  local major_version="${1}"
-  local eol_date="${2}"
-  puts-warn
-  puts-warn "Python ${major_version} reached upstream end-of-life on ${eol_date}, and is"
-  puts-warn "therefore no longer receiving security updates:"
-  puts-warn "https://devguide.python.org/versions/#supported-versions"
-  puts-warn
-  puts-warn "As such, it is no longer supported by this buildpack."
-  puts-warn
-  puts-warn "Please upgrade to a newer Python version."
-  puts-warn
-  puts-warn "For a list of the supported Python versions, see:"
-  puts-warn "https://devcenter.heroku.com/articles/python-support#supported-runtimes"
-  puts-warn
-  meta_set "failure_reason" "python-version-eol"
-  exit 1
-}
-
-# We check for EOL prior to checking if the archive exists on S3, to ensure the more specific EOL error
-# message is still shown for newer stacks where the EOL Python versions might not have been built.
-case "${PYTHON_VERSION}" in
-  python-3.7.+([0-9]))
-    eol_python_version_error "3.7" "June 27th, 2023"
-    ;;
-  python-3.6.+([0-9]))
-    eol_python_version_error "3.6" "December 23rd, 2021"
-    ;;
-  *) ;;
-esac
-
-# The Python runtime archive filename is of form: 'python-X.Y.Z-ubuntu-22.04-amd64.tar.zst'
-# The Ubuntu version is calculated from `STACK` since it's faster than calling `lsb_release`.
-UBUNTU_VERSION="${STACK/heroku-}.04"
-ARCH=$(dpkg --print-architecture)
-PYTHON_URL="${S3_BASE_URL}/${PYTHON_VERSION}-ubuntu-${UBUNTU_VERSION}-${ARCH}.tar.zst"
-
-if ! curl --output /dev/null --silent --head --fail --retry 3 --retry-connrefused --connect-timeout 10 "${PYTHON_URL}"; then
-  puts-warn
-  puts-warn "Requested runtime '${PYTHON_VERSION}' is not available for this stack (${STACK})."
-  puts-warn
-  puts-warn "For a list of the supported Python versions, see:"
-  puts-warn "https://devcenter.heroku.com/articles/python-support#supported-runtimes"
-  puts-warn
-  meta_set "failure_reason" "python-version-not-found"
-  exit 1
-fi
-
-# TODO: Refactor Python version usage to use the non-prefixed form everywhere.
-python_version_without_prefix="${PYTHON_VERSION#python-}"
-meta_set "python_version" "${python_version_without_prefix}"
-meta_set "python_version_major" "${python_version_without_prefix%.*}"
-
-function warn_if_patch_update_available() {
-  local requested_version="${1}"
-  local latest_patch_version="${2}"
-  # Extract the patch version component of the version strings (ie: the '5' in '3.10.5').
-  local requested_patch_number="${requested_version##*.}"
-  local latest_patch_number="${latest_patch_version##*.}"
-  if (( requested_patch_number < latest_patch_number )); then
-    puts-warn
-    puts-warn "A Python security update is available! Upgrade as soon as possible to: ${latest_patch_version}"
-    puts-warn "See: https://devcenter.heroku.com/articles/python-runtimes"
-    puts-warn
-  fi
-}
-
-# We wait until now to display outdated Python version warnings, since we only want to show them
-# if there weren't any errors with the version to avoid adding noise to the error messages.
-case "${PYTHON_VERSION}" in
-  python-3.12.*)
-    warn_if_patch_update_available "${PYTHON_VERSION}" "${LATEST_312}"
-    ;;
-  python-3.11.*)
-    warn_if_patch_update_available "${PYTHON_VERSION}" "${LATEST_311}"
-    ;;
-  python-3.10.*)
-    warn_if_patch_update_available "${PYTHON_VERSION}" "${LATEST_310}"
-    ;;
-  python-3.9.*)
-    warn_if_patch_update_available "${PYTHON_VERSION}" "${LATEST_39}"
-    ;;
-  python-3.8.*)
-    puts-warn
-    puts-warn "Python 3.8 will reach its upstream end-of-life in October 2024, at which"
-    puts-warn "point it will no longer receive security updates:"
-    puts-warn "https://devguide.python.org/versions/#supported-versions"
-    puts-warn
-    puts-warn "Support for Python 3.8 will be removed from this buildpack on December 4th, 2024."
-    puts-warn
-    puts-warn "Upgrade to a newer Python version as soon as possible to keep your app secure."
-    puts-warn "See: https://devcenter.heroku.com/articles/python-runtimes"
-    puts-warn
-    warn_if_patch_update_available "${PYTHON_VERSION}" "${LATEST_38}"
-    ;;
-  # TODO: Make this case an error, since it should be unreachable.
-  *) ;;
-esac
-
-if [[ "$STACK" != "$CACHED_PYTHON_STACK" ]]; then
-    puts-step "Stack has changed from $CACHED_PYTHON_STACK to $STACK, clearing cache"
-    rm -rf .heroku/python-stack .heroku/python-version .heroku/python .heroku/vendor .heroku/python .heroku/python-sqlite3-version
-fi
-
-if [[ -f .heroku/python-version ]]; then
-  if [[ ! "$(cat .heroku/python-version)" == "$PYTHON_VERSION" ]]; then
-      puts-step "Python version has changed from $(cat .heroku/python-version) to ${PYTHON_VERSION}, clearing cache"
-      rm -rf .heroku/python
-  else
-    SKIP_INSTALL=1
-  fi
-fi
-
-# If using Pip, check if we should reinstall python dependencies given that requirements.txt
-# is non-deterministic (not all packages pinned, doesn't handle uninstalls etc). We don't need
-# to do this when using Pipenv, since it has a lockfile and syncs the packages for us.
-if [[ -f "${BUILD_DIR}/requirements.txt" ]]; then
-  if [[ ! -f "$CACHE_DIR/.heroku/requirements.txt" ]]; then
-    # This is a the first build of an app (or the build cache was cleared). Since there
-    # are no cached packages, we only need to store the requirements file for next time.
-    cp -R "$BUILD_DIR/requirements.txt" "$CACHE_DIR/.heroku/requirements.txt"
-  else
-    # IF there IS a cached directory, check for differences with the new one
-    if ! diff "$BUILD_DIR/requirements.txt" "$CACHE_DIR/.heroku/requirements.txt" &> /dev/null; then
-      puts-step "Requirements file has been changed, clearing cached dependencies"
-      # if there are any differences, clear the Python cache
-      # Installing Python over again does not take noticably more time
-      cp -R "$BUILD_DIR/requirements.txt" "$CACHE_DIR/.heroku/requirements.txt"
-      rm -rf .heroku/python
-      unset SKIP_INSTALL
-    else
-      puts-step "No change in requirements detected, installing from cache"
-    fi
-  fi
-fi
-
-if [[ -n "${SKIP_INSTALL}" ]]; then
-  puts-step "Using cached install of ${PYTHON_VERSION}"
-else
-  puts-step "Installing ${PYTHON_VERSION}"
-
-  # Prepare destination directory.
-  mkdir -p .heroku/python
-
-  if ! curl --silent --show-error --fail --retry 3 --retry-connrefused --connect-timeout 10 "${PYTHON_URL}" | tar --zstd --extract --directory .heroku/python; then
-    # The Python version was confirmed to exist previously, so any failure here is due to
-    # a networking issue or archive/buildpack bug rather than the runtime not existing.
-    puts-warn "Failed to download/install ${PYTHON_VERSION}"
-    meta_set "failure_reason" "python-download"
-    exit 1
-  fi
-
-  # Record for future reference.
-  echo "$PYTHON_VERSION" > .heroku/python-version
-  echo "$STACK" > .heroku/python-stack
-
-  hash -r
-fi
-
-PIP_VERSION=$(get_requirement_version 'pip')
-SETUPTOOLS_VERSION=$(get_requirement_version 'setuptools')
-WHEEL_VERSION=$(get_requirement_version 'wheel')
-
-puts-step "Installing pip ${PIP_VERSION}, setuptools ${SETUPTOOLS_VERSION} and wheel ${WHEEL_VERSION}"
-
-meta_set "pip_version" "${PIP_VERSION}"
-meta_set "setuptools_version" "${SETUPTOOLS_VERSION}"
-meta_set "wheel_version" "${WHEEL_VERSION}"
-
-# Python bundles Pip within its standard library, which we can use to install our chosen
-# pip version from PyPI, saving us from having to download the usual pip bootstrap script.
-# We have to use a glob since the bundled wheel filename contains the pip version, which
-# differs between Python versions. We also have to handle the case where there are multiple
-# matching pip wheels, since in some versions of Python (eg 3.9.0) multiple versions of pip
-# were accidentally bundled upstream. Note: This implementation relies upon `nullglob` being
-# set, which is the case thanks to the `bin/utils` that was run earlier.
-BUNDLED_PIP_WHEEL_LIST=(.heroku/python/lib/python*/ensurepip/_bundled/pip-*.whl)
-BUNDLED_PIP_WHEEL="${BUNDLED_PIP_WHEEL_LIST[0]}"
-
-if [[ -z "${BUNDLED_PIP_WHEEL}" ]]; then
-  puts-warn "Failed to locate the bundled pip wheel"
-  meta_set "failure_reason" "bundled-pip-not-found"
-  exit 1
-fi
-
-/app/.heroku/python/bin/python "${BUNDLED_PIP_WHEEL}/pip" install --quiet --disable-pip-version-check --no-cache-dir \
-  "pip==${PIP_VERSION}" "setuptools==${SETUPTOOLS_VERSION}" "wheel==${WHEEL_VERSION}"
-
-hash -r
diff --git a/bin/steps/sqlite3 b/bin/steps/sqlite3
deleted file mode 100755
index f21d606f4..000000000
--- a/bin/steps/sqlite3
+++ /dev/null
@@ -1,80 +0,0 @@
-#!/usr/bin/env bash
-
-# TODO: Remove this entirely since the Python stdlib now includes modern sqlite support,
-# and the APT buildpack should be used if an app needs the sqlite CLI/headers.
-
-sqlite3_install() {
-  HEROKU_PYTHON_DIR="$1"
-  HEADERS_ONLY="$3"
-
-  mkdir -p "$HEROKU_PYTHON_DIR"
-
-  APT_CACHE_DIR="$HEROKU_PYTHON_DIR/apt/cache"
-  APT_STATE_DIR="$HEROKU_PYTHON_DIR/apt/state"
-
-  mkdir -p "$APT_CACHE_DIR/archives/partial"
-  mkdir -p "$APT_STATE_DIR/lists/partial"
-
-  APT_OPTIONS=(
-    "--option=debug::nolocking=true"
-    "--option=dir::cache=${APT_CACHE_DIR}"
-    "--option=dir::state=${APT_STATE_DIR}"
-    "--option=dir::etc::sourcelist=/etc/apt/sources.list"
-  )
-
-  apt-get "${APT_OPTIONS[@]}" update > /dev/null 2>&1
-  if [[ -z "$HEADERS_ONLY" ]]; then
-    apt-get "${APT_OPTIONS[@]}" -y -d --reinstall install libsqlite3-dev sqlite3 > /dev/null 2>&1
-  else
-    apt-get "${APT_OPTIONS[@]}" -y -d --reinstall install libsqlite3-dev
-  fi
-
-  find "$APT_CACHE_DIR/archives/" -name "*.deb" -exec dpkg -x {} "$HEROKU_PYTHON_DIR/sqlite3/" \;
-
-  mkdir -p "$HEROKU_PYTHON_DIR/include"
-  mkdir -p "$HEROKU_PYTHON_DIR/lib"
-
-  # remove old sqlite3 libraries/binaries
-  find "$HEROKU_PYTHON_DIR/include/" -name "sqlite3*.h" -exec rm -f {} \;
-  find "$HEROKU_PYTHON_DIR/lib/" -name "libsqlite3.*" -exec rm -f {} \;
-  rm -f "$HEROKU_PYTHON_DIR/lib/pkgconfig/sqlite3.pc"
-  rm -f "$HEROKU_PYTHON_DIR/bin/sqlite3"
-
-  # eg: `x86_64` or `aarch64`
-  GNU_ARCH=$(arch)
-
-  # copy over sqlite3 headers & bins and setup linking against the stack image library
-  mv "$HEROKU_PYTHON_DIR/sqlite3/usr/include/"* "$HEROKU_PYTHON_DIR/include/"
-  mv "$HEROKU_PYTHON_DIR/sqlite3/usr/lib/${GNU_ARCH}-linux-gnu"/libsqlite3.*a "$HEROKU_PYTHON_DIR/lib/"
-  mkdir -p "$HEROKU_PYTHON_DIR/lib/pkgconfig"
-  # set the right prefix/lib directories
-  sed -e 's/prefix=\/usr/prefix=\/app\/.heroku\/python/' -e "s/\/${GNU_ARCH}-linux-gnu//" "$HEROKU_PYTHON_DIR/sqlite3/usr/lib/${GNU_ARCH}-linux-gnu/pkgconfig/sqlite3.pc" > "$HEROKU_PYTHON_DIR/lib/pkgconfig/sqlite3.pc"
-  # need to point the libsqlite3.so to the stack image library for /usr/bin/ld -lsqlite3
-  SQLITE3_LIBFILE="/usr/lib/${GNU_ARCH}-linux-gnu/$(readlink -n "$HEROKU_PYTHON_DIR/sqlite3/usr/lib/${GNU_ARCH}-linux-gnu/libsqlite3.so")"
-  ln -s "$SQLITE3_LIBFILE" "$HEROKU_PYTHON_DIR/lib/libsqlite3.so"
-  if [[ -z "$HEADERS_ONLY" ]]; then
-    mv "$HEROKU_PYTHON_DIR/sqlite3/usr/bin"/* "$HEROKU_PYTHON_DIR/bin/"
-  fi
-
-  # cleanup
-  rm -rf "$HEROKU_PYTHON_DIR/sqlite3/"
-  rm -rf "$HEROKU_PYTHON_DIR/apt/"
-}
-
-buildpack_sqlite3_install() {
-  puts-step "Installing SQLite3"
-
-  # TODO: This never actual prints failure or even aborts the build, since
-  # the conditional disables `set -e` inside the called function:
-  # https://stackoverflow.com/q/19789102
-  # ...plus whoever wrote this forgot the `exit 1` in the `else` anyway.
-  if sqlite3_install "$BUILD_DIR/.heroku/python" ; then
-    # mcount "success.python.sqlite3"
-    :
-  else
-    echo "Sqlite3 failed to install."
-    # mcount "failure.python.sqlite3"
-  fi
-
-  mkdir -p "$CACHE_DIR/.heroku/"
-}
diff --git a/bin/test-compile b/bin/test-compile
index 03fd6fadb..1fef46275 100755
--- a/bin/test-compile
+++ b/bin/test-compile
@@ -3,6 +3,7 @@
 # See: https://devcenter.heroku.com/articles/testpack-api
 
 set -euo pipefail
+shopt -s inherit_errexit
 
 # The absolute path to the root of the buildpack.
 BUILDPACK_DIR=$(cd "$(dirname "$(dirname "${BASH_SOURCE[0]}")")" && pwd)
diff --git a/bin/utils b/bin/utils
index 5ce22d866..3eedc1f81 100755
--- a/bin/utils
+++ b/bin/utils
@@ -5,70 +5,15 @@
 shopt -s extglob
 shopt -s nullglob
 
-source "${BUILDPACK_DIR}/vendor/buildpack-stdlib_v8.sh"
-
-if [[ "$(uname)" == "Darwin" ]]; then
-    sed() { command sed -l "$@"; }
-else
-    sed() { command sed -u "$@"; }
-fi
-
-# Syntax sugar.
-indent() {
-  sed "s/^/       /"
-}
-
-
-# Clean up pip output
-cleanup() {
-  sed -e 's/\.\.\.\+/.../g' | sed -e '/already satisfied/Id' | sed -e '/No files were found to uninstall/Id' | sed -e '/Overwriting/Id' | sed -e '/python executable/Id' | sed -e '/no previously-included files/Id'
-}
-
-# Buildpack Steps.
-puts-step() {
-  echo "-----> $*"
-}
-
-# Buildpack Warnings.
-puts-warn() {
-  echo " !     $*"
-}
-
-# Does some serious copying.
-deep-cp() {
-  declare source="$1" target="$2"
-
-  mkdir -p "$target"
-
-  # cp doesn't like being called without source params,
-  # so make sure they expand to something first.
-  # subshell to avoid surprising caller with shopts.
-  (
-    shopt -s nullglob dotglob
-    set -- "$source"/!(tmp|.|..)
-    [[ $# == 0 ]] || cp -a "$@" "$target"
-  )
-}
+source "${BUILDPACK_DIR:?}/vendor/buildpack-stdlib_v8.sh"
 
 # Measure the size of the Python installation.
 measure-size() {
-  { du -s .heroku/python 2>/dev/null || echo 0; } | awk '{print $1}'
+	{ du -s .heroku/python 2>/dev/null || echo 0; } | awk '{print $1}'
 }
 
 # Returns 0 if the specified module exists, otherwise returns 1.
 is_module_available() {
-  local module_name="${1}"
-  python -c "import sys, importlib.util; sys.exit(0 if importlib.util.find_spec('${module_name}') else 1)"
-}
-
-# The requirement versions are effectively buildpack constants, however, we want
-# Dependabot to be able to update them, which requires that they be in requirements
-# files. The requirements files contain contents like `package==1.2.3` (and not just
-# the package version) so we have to extract the version substring from it.
-get_requirement_version() {
-  local package_name="${1}"
-  local requirement
-  requirement=$(cat "${BUILDPACK_DIR}/requirements/${package_name}.txt")
-  local requirement_version="${requirement#"${package_name}=="}"
-  echo "${requirement_version}"
+	local module_name="${1}"
+	python -c "import sys, importlib.util; sys.exit(0 if importlib.util.find_spec('${module_name}') else 1)"
 }
diff --git a/bin/warnings b/bin/warnings
index 0036f5ccc..04b453a2d 100755
--- a/bin/warnings
+++ b/bin/warnings
@@ -1,14 +1,51 @@
 #!/usr/bin/env bash
 
-gdal-missing() {
-  if grep -qi 'Could not find gdal-config' "$WARNINGS_LOG"; then
-    echo
-    puts-warn "Hello! Package installation failed since the GDAL library was not found."
-    puts-warn "For GDAL, GEOS and PROJ support, use the Geo buildpack alongside the Python buildpack:"
-    puts-warn "https://github.com/heroku/heroku-geo-buildpack"
-  fi
-}
-
 show-warnings() {
-  gdal-missing
+	local install_log="${1}"
+
+	# shellcheck disable=SC2154 # TODO: Env var is referenced but not assigned.
+	if grep -qi 'Could not find gdal-config' "${install_log}"; then
+		output::error <<-'EOF'
+			Error: Package installation failed since the GDAL library wasn't found.
+
+			For GDAL, GEOS and PROJ support, use the Geo buildpack alongside the Python buildpack:
+			https://github.com/heroku/heroku-geo-buildpack
+		EOF
+		build_data::set_string "failure_detail" "Could not find gdal-config"
+	elif grep -qi 'sqlite3.h: No such file or directory' "${install_log}"; then
+		output::error <<-'EOF'
+			Error: Package installation failed since SQLite headers weren't found.
+
+			The Python buildpack no longer installs the SQLite headers
+			package since most apps don't require it.
+
+			If you're trying to install the `pysqlite3` package, we
+			recommend using the virtually identical `sqlite3` module in
+			Python's standard library instead:
+			https://docs.python.org/3/library/sqlite3.html
+
+			To do this:
+			1. Remove the `pysqlite3` package from your dependencies.
+			2. Replace any `pysqlite3` imports in your app with `sqlite3`.
+
+			Alternatively, if you can't use the `sqlite3` stdlib module,
+			update your `pysqlite3` package to 0.6.0 or newer, since the
+			newer versions are published with pre-compiled wheels and so
+			don't need the SQLite headers to be installed.
+		EOF
+		build_data::set_string "failure_detail" "sqlite3.h: No such file or directory"
+	elif grep -qi 'Please use pip<24.1 if you need to use this version' "${install_log}"; then
+		output::error <<-'EOF'
+			Error: One of your dependencies contains broken metadata.
+
+			Newer versions of pip reject packages that use invalid versions
+			in their metadata (such as Celery older than v5.2.1).
+
+			Try upgrading to a newer version of the affected package.
+
+			For more help, see:
+			https://devcenter.heroku.com/changelog-items/3073
+		EOF
+		build_data::set_string "failure_detail" "Please use pip<24.1 if you need to use this version"
+	fi
 }
diff --git a/buildpack.toml b/buildpack.toml
index 0464f13c9..4ccd6f242 100644
--- a/buildpack.toml
+++ b/buildpack.toml
@@ -5,9 +5,12 @@ name = "Python"
 files = [
   ".github/",
   "builds/",
+  "etc/publish.sh",
   "spec/",
+  ".editorconfig",
   ".gitignore",
   ".rubocop.yml",
+  ".shellcheckrc",
   "Gemfile",
   "Gemfile.lock",
   "hatchet.json",
diff --git a/builds/Dockerfile b/builds/Dockerfile
index f3fcfffb7..e2a56b2db 100644
--- a/builds/Dockerfile
+++ b/builds/Dockerfile
@@ -1,4 +1,5 @@
 ARG STACK_VERSION="24"
+FROM ghcr.io/sigstore/cosign/cosign:v3.1.1@sha256:6bbe0d281d955c79f85b325f0f7e651c1bcab5a4fa4ad4903d74955178a3b2eb AS cosign
 FROM heroku/heroku:${STACK_VERSION}-build
 
 ARG STACK_VERSION
@@ -7,12 +8,17 @@ ENV STACK="heroku-${STACK_VERSION}"
 # For Heroku-24 and newer, the build image sets a non-root default `USER`.
 USER root
 
+# `libcrypt-dev` can be removed once we drop support for Python 3.12,
+# since the `crypt` module was removed in Python 3.13:
+# https://docs.python.org/3.13/whatsnew/3.13.html#whatsnew313-pep594
 RUN apt-get update --error-on=any \
     && apt-get install -y --no-install-recommends \
+      libcrypt-dev \
       libdb-dev \
       libreadline-dev \
       libsqlite3-dev \
     && rm -rf /var/lib/apt/lists/*
+COPY --from=cosign /ko-app/cosign /usr/local/bin/cosign
 
 WORKDIR /tmp
 COPY build_python_runtime.sh .
diff --git a/builds/build_python_runtime.sh b/builds/build_python_runtime.sh
index b1e81c7b8..c19f155bb 100755
--- a/builds/build_python_runtime.sh
+++ b/builds/build_python_runtime.sh
@@ -1,6 +1,11 @@
 #!/usr/bin/env bash
 
+# This script is used by buildpack maintainers to compile new Python versions as they are released,
+# ready for upload to S3. (It isn't run as part of normal buildpack execution during app builds.)
+# See `builds/README.md` for how to invoke this via GitHub Actions.
+
 set -euo pipefail
+shopt -s inherit_errexit
 
 PYTHON_VERSION="${1:?"Error: The Python version to build must be specified as the first argument."}"
 PYTHON_MAJOR_VERSION="${PYTHON_VERSION%.*}"
@@ -14,78 +19,66 @@ INSTALL_DIR="/tmp/python"
 SRC_DIR="/tmp/src"
 UPLOAD_DIR="/tmp/upload"
 
-function error() {
-  echo "Error: ${1}" >&2
-  exit 1
+function abort() {
+	echo "Error: ${1}" >&2
+	exit 1
 }
 
-case "${STACK}" in
-  heroku-24)
-    SUPPORTED_PYTHON_VERSIONS=(
-      "3.10"
-      "3.11"
-      "3.12"
-    )
-    ;;
-  heroku-22)
-    SUPPORTED_PYTHON_VERSIONS=(
-      "3.9"
-      "3.10"
-      "3.11"
-      "3.12"
-    )
-    ;;
-  heroku-20)
-    SUPPORTED_PYTHON_VERSIONS=(
-      "3.8"
-      "3.9"
-      "3.10"
-      "3.11"
-      "3.12"
-    )
-    ;;
-  *)
-    error "Error: Unsupported stack '${STACK}'!"
-    ;;
+case "${STACK:?}" in
+	heroku-22 | heroku-24 | heroku-26)
+		SUPPORTED_PYTHON_VERSIONS=(
+			"3.10"
+			"3.11"
+			"3.12"
+			"3.13"
+			"3.14"
+		)
+		;;
+	*)
+		abort "Unsupported stack '${STACK}'!"
+		;;
 esac
 
-if [[ ! " ${SUPPORTED_PYTHON_VERSIONS[*]} " == *" ${PYTHON_MAJOR_VERSION} "* ]]; then
-  error "Error: Python ${PYTHON_MAJOR_VERSION} is not supported on ${STACK}!"
+if [[ " ${SUPPORTED_PYTHON_VERSIONS[*]} " != *" ${PYTHON_MAJOR_VERSION} "* ]]; then
+	abort "Python ${PYTHON_MAJOR_VERSION} isn't supported on ${STACK}!"
 fi
 
-# The release keys can be found on https://www.python.org/downloads/ -> "OpenPGP Public Keys".
+# Sigstore identities taken from: https://www.python.org/downloads/metadata/sigstore/
 case "${PYTHON_MAJOR_VERSION}" in
-  3.12)
-    # https://github.com/Yhg1s.gpg
-    GPG_KEY_FINGERPRINT='7169605F62C751356D054A26A821E680E5FA6305'
-    ;;
-  3.10|3.11)
-    # https://keybase.io/pablogsal/
-    GPG_KEY_FINGERPRINT='A035C8C19219BA821ECEA86B64E628F8D684696D'
-    ;;
-  3.8|3.9)
-    # https://keybase.io/ambv/
-    GPG_KEY_FINGERPRINT='E3FF2839C048B25C084DEBE9B26995E310250568'
-    ;;
-  *)
-    error "Error: Unsupported Python version '${PYTHON_MAJOR_VERSION}'!"
-    ;;
+	3.14)
+		SIGSTORE_IDENTITY='hugo@python.org'
+		SIGSTORE_ISSUER='https://github.com/login/oauth'
+		;;
+	3.12 | 3.13)
+		SIGSTORE_IDENTITY='thomas@python.org'
+		SIGSTORE_ISSUER='https://accounts.google.com'
+		;;
+	3.10 | 3.11)
+		SIGSTORE_IDENTITY='pablogsal@python.org'
+		SIGSTORE_ISSUER='https://accounts.google.com'
+		;;
+	*)
+		abort "Unsupported Python version '${PYTHON_MAJOR_VERSION}'!"
+		;;
 esac
 
 echo "Building Python ${PYTHON_VERSION} for ${STACK} (${ARCH})..."
 
 SOURCE_URL="https://www.python.org/ftp/python/${PYTHON_VERSION}/Python-${PYTHON_VERSION}.tgz"
-SIGNATURE_URL="${SOURCE_URL}.asc"
+SIGSTORE_BUNDLE_URL="${SOURCE_URL}.sigstore"
 
 set -o xtrace
 
 mkdir -p "${SRC_DIR}" "${INSTALL_DIR}" "${UPLOAD_DIR}"
 
-curl --fail --retry 3 --retry-connrefused --connect-timeout 10 --max-time 60 -o python.tgz "${SOURCE_URL}"
-curl --fail --retry 3 --retry-connrefused --connect-timeout 10 --max-time 60 -o python.tgz.asc "${SIGNATURE_URL}"
+curl --fail --retry 5 --retry-connrefused --connect-timeout 3 --max-time 30 -o python.tgz "${SOURCE_URL}"
+curl --fail --retry 5 --retry-connrefused --connect-timeout 3 --max-time 30 -o python.tgz.sigstore "${SIGSTORE_BUNDLE_URL}"
 
-gpg --batch --verbose --recv-keys "${GPG_KEY_FINGERPRINT}"
-gpg --batch --verify python.tgz.asc python.tgz
+cosign verify-blob \
+	--bundle python.tgz.sigstore \
+	--certificate-identity "${SIGSTORE_IDENTITY}" \
+	--certificate-oidc-issuer "${SIGSTORE_ISSUER}" \
+	python.tgz
 
 tar --extract --file python.tgz --strip-components=1 --directory "${SRC_DIR}"
 cd "${SRC_DIR}"
@@ -94,59 +87,48 @@ cd "${SRC_DIR}"
 # for maximum compatibility / most battle-tested build configuration:
 # https://github.com/docker-library/python
 CONFIGURE_OPTS=(
-  # Explicitly set the target architecture rather than auto-detecting based on the host CPU.
-  # This only affects targets like i386 (for which we don't build), but we pass it anyway for
-  # completeness and parity with the Python Docker image builds.
-  "--build=$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)"
-  # Support loadable extensions in the `_sqlite` extension module.
-  "--enable-loadable-sqlite-extensions"
-  # Enable recommended release build performance optimisations such as PGO.
-  "--enable-optimizations"
-  # Make autoconf's configure option validation more strict.
-  "--enable-option-checking=fatal"
-  # Install Python into `/tmp/python` rather than the default of `/usr/local`.
-  "--prefix=${INSTALL_DIR}"
-  # Skip running `ensurepip` as part of install, since the buildpack installs a curated
-  # version of pip itself (which ensures it's consistent across Python patch releases).
-  "--with-ensurepip=no"
-  # Build the `pyexpat` module using the `expat` library in the base image (which will
-  # automatically receive security updates), rather than CPython's vendored version.
-  "--with-system-expat"
+	# Explicitly set the target architecture rather than auto-detecting based on the host CPU.
+	# This only affects targets like i386 (for which we don't build), but we pass it anyway for
+	# completeness and parity with the Python Docker image builds.
+	"--build=$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)"
+	# Support loadable extensions in the `_sqlite` extension module.
+	"--enable-loadable-sqlite-extensions"
+	# Enable recommended release build performance optimisations such as PGO.
+	"--enable-optimizations"
+	# Make autoconf's configure option validation more strict.
+	"--enable-option-checking=fatal"
+	# Shared builds are beneficial for a number of reasons:
+	# - Reduces the size of the build, since it avoids the duplication between
+	#   the Python binary and the static library.
+	# - Permits use-cases that only work with the shared Python library,
+	#   and not the static library (such as `pycall.rb` or `PyO3`).
+	# - More consistent with the official Python Docker images and other distributions.
+	#
+	# Shared builds are slower unless `no-semantic-interposition` and LTO are used,
+	# however, as of Python 3.10 `no-semantic-interposition` is enabled by default:
+	# https://fedoraproject.org/wiki/Changes/PythonNoSemanticInterpositionSpeedup
+	# https://github.com/python/cpython/issues/83161
+	"--enable-shared"
+	# Install Python into `/tmp/python` rather than the default of `/usr/local`.
+	"--prefix=${INSTALL_DIR}"
+	# Skip running `ensurepip` as part of install, since the buildpack installs a curated
+	# version of pip itself (which ensures it's consistent across Python patch releases).
+	"--with-ensurepip=no"
+	"--with-lto"
+	# Counter-intuitively, the static library is still generated by default even when
+	# the shared library is enabled, so we disable it to reduce the build size.
+	# This option only exists for Python 3.10+.
+	"--without-static-libpython"
 )
 
-if [[ "${PYTHON_MAJOR_VERSION}" != 3.[8-9] ]]; then
-  CONFIGURE_OPTS+=(
-    # Shared builds are beneficial for a number of reasons:
-    # - Reduces the size of the build, since it avoids the duplication between
-    #   the Python binary and the static library.
-    # - Permits use-cases that only work with the shared Python library,
-    #   and not the static library (such as `pycall.rb` or `PyO3`).
-    # - More consistent with the official Python Docker images and other distributions.
-    #
-    # However, shared builds are slower unless `no-semantic-interposition`and LTO is used:
-    # https://fedoraproject.org/wiki/Changes/PythonNoSemanticInterpositionSpeedup
-    # https://github.com/python/cpython/issues/83161
-    #
-    # It's only as of Python 3.10 that `no-semantic-interposition` is enabled by default,
-    # so we only use shared builds on Python 3.10+ to avoid needing to override the default
-    # compiler flags.
-    "--enable-shared"
-    "--with-lto"
-    # Counter-intuitively, the static library is still generated by default even when
-    # the shared library is enabled, so we disable it to reduce the build size.
-    # This option only exists for Python 3.10+.
-    "--without-static-libpython"
-  )
-fi
-
-if [[ "${PYTHON_MAJOR_VERSION}" == "3.11" || "${PYTHON_MAJOR_VERSION}" == "3.12" ]]; then
-  CONFIGURE_OPTS+=(
-    # Skip building the test modules, since we remove them after the build anyway.
-    # This feature was added in Python 3.10+, however it wasn't until Python 3.11
-    # that compatibility issues between it and PGO were fixed:
-    # https://github.com/python/cpython/pull/29315
-    "--disable-test-modules"
-  )
+if [[ "${PYTHON_MAJOR_VERSION}" != +(3.10) ]]; then
+	CONFIGURE_OPTS+=(
+		# Skip building the test modules, since we remove them after the build anyway.
+		# This feature was added in Python 3.10, however it wasn't until Python 3.11
+		# that compatibility issues between it and PGO were fixed:
+		# https://github.com/python/cpython/pull/29315
+		"--disable-test-modules"
+	)
 fi
 
 ./configure "${CONFIGURE_OPTS[@]}"
@@ -160,31 +142,15 @@ fi
 # - https://wiki.ubuntu.com/ToolChain/CompilerFlags
 # - https://wiki.debian.org/Hardening
 # - https://github.com/docker-library/python/issues/810
-# We only use `dpkg-buildflags` for Python versions where we build in shared mode (Python 3.9+),
-# since some of the options it enables interferes with the stripping of static libraries.
-if [[ "${PYTHON_MAJOR_VERSION}" == 3.[8-9] ]]; then
-  EXTRA_CFLAGS=''
-  LDFLAGS='-Wl,--strip-all'
-else
-  EXTRA_CFLAGS="$(dpkg-buildflags --get CFLAGS)"
-  LDFLAGS="$(dpkg-buildflags --get LDFLAGS) -Wl,--strip-all"
-fi
+EXTRA_CFLAGS="$(dpkg-buildflags --get CFLAGS)"
+LDFLAGS="$(dpkg-buildflags --get LDFLAGS) -Wl,--strip-all"
 
-make -j "$(nproc)" "EXTRA_CFLAGS=${EXTRA_CFLAGS}" "LDFLAGS=${LDFLAGS}"
+CPU_COUNT="$(nproc)"
+make -j "${CPU_COUNT}" "EXTRA_CFLAGS=${EXTRA_CFLAGS}" "LDFLAGS=${LDFLAGS}"
 make install
 
-if [[ "${PYTHON_MAJOR_VERSION}" == 3.[8-9] ]]; then
-  # On older versions of Python we're still building the static library, which has to be
-  # manually stripped since the linker stripping enabled in LDFLAGS doesn't cover them.
-  # We're using `--strip-unneeded` since `--strip-all` would remove the `.symtab` section
-  # that is required for static libraries to be able to be linked.
-  # `find` is used since there are multiple copies of the static library in version-specific
-  # locations, eg:
-  #   - `lib/libpython3.9.a`
-  #   - `lib/python3.9/config-3.9-x86_64-linux-gnu/libpython3.9.a`
-  find "${INSTALL_DIR}" -type f -name '*.a' -print -exec strip --strip-unneeded '{}' +
-elif ! find "${INSTALL_DIR}" -type f -name '*.a' -print -exec false '{}' +; then
-  error "Error: Unexpected static libraries found!"
+if ! find "${INSTALL_DIR}" -type f -name '*.a' -print -exec false '{}' +; then
+	abort "Unexpected static libraries found!"
 fi
 
 # Remove unneeded test directories, similar to the official Docker Python images:
@@ -218,6 +184,16 @@ find "${INSTALL_DIR}" -depth -type f -name "*.pyc" -delete
 # https://github.com/python/cpython/blob/v3.11.3/Makefile.pre.in#L2087-L2113
 LD_LIBRARY_PATH="${SRC_DIR}" "${SRC_DIR}/python" -m compileall -f --invalidation-mode unchecked-hash --workers 0 "${INSTALL_DIR}"
 
+# Delete entrypoint scripts (and their symlinks) that don't work with relocated Python since they
+# hardcode the Python install directory in their shebangs (e.g. `#!/tmp/python/bin/python3.NN`).
+# These scripts are rarely used in production, and can still be accessed via their Python module
+# (e.g. `python -m pydoc`) if needed.
+rm "${INSTALL_DIR}"/bin/{idle,pydoc}*
+# The 2to3 module and entrypoint was removed from the stdlib in Python 3.13.
+if [[ "${PYTHON_MAJOR_VERSION}" == +(3.10|3.11|3.12) ]]; then
+	rm "${INSTALL_DIR}"/bin/2to3*
+fi
+
 # Support using Python 3 via the version-less `python` command, for parity with virtualenvs,
 # the Python Docker images and to also ensure buildpack Python shadows any installed system
 # Python, should that provide a version-less alias too.
diff --git a/builds/test_python_runtime.sh b/builds/test_python_runtime.sh
index 258600a31..36c3d114f 100755
--- a/builds/test_python_runtime.sh
+++ b/builds/test_python_runtime.sh
@@ -1,9 +1,17 @@
 #!/usr/bin/env bash
 
 set -euo pipefail
+shopt -s inherit_errexit
 
 ARCHIVE_FILEPATH="${1:?"Error: The filepath of the Python runtime archive must be specified as the first argument."}"
 
+function abort() {
+	echo "Error: ${1}" >&2
+	exit 1
+}
+
+set -x
+
 # We intentionally extract the Python runtime into a different directory to the one into which it
 # was originally installed before being packaged, to check that relocation works (since buildpacks
 # depend on it). Since the Python binary was built in shared mode, `LD_LIBRARY_PATH` must be set
@@ -13,36 +21,74 @@ export LD_LIBRARY_PATH="${INSTALL_DIR}/lib/"
 
 tar --zstd --extract --verbose --file "${ARCHIVE_FILEPATH}" --directory "${INSTALL_DIR}"
 
-# Check Python is able to start and is usable via both the default `python3` command and the
-# `python` symlink we create during the build. We use the full filepath rather than adding the
+# Check Python is able to start and is usable via both the default `python3` + `python3.XX` commands
+# and the `python` symlink we create during the build. We use the full filepath rather than adding the
 # directory to PATH to ensure the test doesn't pass because of falling through to system Python.
 "${INSTALL_DIR}/bin/python3" --version
+major_python_version="$("${INSTALL_DIR}/bin/python3" -c "import sys; print(f'{sys.version_info.major}.{sys.version_info.minor}')")"
+"${INSTALL_DIR}/bin/python${major_python_version}" --version
 "${INSTALL_DIR}/bin/python" --version
 
+# Check the Python config script still exists/works after the deletion of scripts with broken shebang lines.
+"${INSTALL_DIR}/bin/python3-config" --help
+
+set +x
+
+# Check that the broken bin entrypoints and symlinks (such as `idle3` and `pydoc3`) were deleted.
+UNEXPECTED_BIN_FILES="$(find "${INSTALL_DIR}/bin" -type 'f,l' -not -name 'python*')"
+if [[ -n "${UNEXPECTED_BIN_FILES}" ]]; then
+	echo "${UNEXPECTED_BIN_FILES}"
+	abort "The above files were found in the bin/ directory but weren't expected!"
+else
+	echo "No unexpected files found in the bin/ directory."
+fi
+
 # Check that all dynamically linked libraries exist in the run image (since it has fewer packages than the build image).
 LDD_OUTPUT=$(find "${INSTALL_DIR}" -type f,l \( -name 'python3' -o -name '*.so*' \) -exec ldd '{}' +)
 if grep 'not found' <<<"${LDD_OUTPUT}" | sort --unique; then
-  echo "The above dynamically linked libraries were not found!"
-  exit 1
+	abort "The above dynamically linked libraries weren't found!"
+else
+	echo "All dynamically linked libraries were found."
 fi
 
 # Check that optional and/or system library dependent stdlib modules were built.
 optional_stdlib_modules=(
-  _uuid
-  bz2
-  ctypes
-  curses
-  dbm.gnu
-  dbm.ndbm
-  decimal
-  lzma
-  readline
-  sqlite3
-  ssl
-  xml.parsers.expat
-  zlib
+	_uuid
+	bz2
+	ctypes
+	curses
+	dbm.gnu
+	dbm.ndbm
+	decimal
+	lzma
+	readline
+	sqlite3
+	ssl
+	xml.parsers.expat
+	zlib
 )
-if ! "${INSTALL_DIR}/bin/python3" -c "import $(IFS=, ; echo "${optional_stdlib_modules[*]}")"; then
-  echo "The above optional stdlib module failed to import! Check the compile logs to see if it was skipped due to missing libraries/headers."
-  exit 1
+
+# zstd support was added in Python 3.14:
+# https://docs.python.org/3.14/whatsnew/3.14.html#whatsnew314-zstandard
+if [[ "${major_python_version}" == "3.14" ]]; then
+	optional_stdlib_modules+=(
+		compression.zstd
+	)
+fi
+
+# crypt was removed in Python 3.13:
+# https://docs.python.org/3.13/whatsnew/3.13.html#whatsnew313-pep594
+if [[ "${major_python_version}" == +(3.10|3.11|3.12) ]]; then
+	optional_stdlib_modules+=(
+		crypt
+	)
+fi
+
+if "${INSTALL_DIR}/bin/python3" -c "import $(
+	IFS=,
+	echo "${optional_stdlib_modules[*]}"
+)"; then
+	echo "Successfully imported: ${optional_stdlib_modules[*]}"
+else
+	abort "The above optional stdlib module failed to import! Check the compile logs to see if it was skipped due to missing libraries/headers."
 fi
diff --git a/etc/publish.sh b/etc/publish.sh
index c7801efe2..019bf60d3 100755
--- a/etc/publish.sh
+++ b/etc/publish.sh
@@ -1,26 +1,65 @@
 #!/usr/bin/env bash
 
 set -euo pipefail
+shopt -s inherit_errexit
 
-BP_NAME=${1:-"heroku/python"}
+buildpack_registry_name="heroku/python"
 
-curVersion=$(heroku buildpacks:versions "$BP_NAME" | awk 'FNR == 3 { print $1 }')
-newVersion="v$((curVersion + 1))"
+function abort() {
+	echo
+	echo "Error: ${1}" >&2
+	exit 1
+}
 
-read -r -p "Deploy as version: $newVersion [y/n]? " choice
-case "$choice" in
-  y|Y ) echo "";;
-  n|N ) exit 0;;
-  * ) exit 1;;
-esac
+echo "Checking environment..."
+
+if ! command -v gh >/dev/null; then
+	abort "Install the GitHub CLI first: https://cli.github.com"
+fi
+
+if ! heroku buildpacks:publish --help >/dev/null; then
+	abort "Install the Buildpack Registry plugin first: https://github.com/heroku/plugin-buildpack-registry"
+fi
+
+# Explicitly check the CLI is logged in, since the Buildpack Registry plugin doesn't handle re-authing
+# expired logins properly, which can otherwise lead to the release aborting partway through.
+if ! heroku whoami >/dev/null; then
+	abort "Log into the Heroku CLI first: heroku login"
+fi
+
+echo "Checking buildpack versions in sync..."
+current_github_release_version=$(gh release view --json tagName --jq '.tagName' | tr --delete 'v')
+current_registry_version="$(heroku buildpacks:versions "${buildpack_registry_name}" | awk 'FNR == 3 { print $1 }')"
+
+if [[ "${current_github_release_version}" != "${current_registry_version}" ]]; then
+	abort "The current GitHub release version (v${current_github_release_version}) doesn't match the registry version (v${current_registry_version}), likely due to a registry rollback. Fix this first!"
+fi
 
+new_version="$((current_github_release_version + 1))"
+new_git_tag="v${new_version}"
+
+echo "Extracting changelog entry for this release..."
 git fetch origin
-originMain=$(git rev-parse origin/main)
-echo "Tagging commit $originMain with $newVersion... "
-git tag "$newVersion" "${originMain:?}"
-git push origin "refs/tags/${newVersion}"
+# Using `git show` to avoid having to disrupt the current branch/working directory.
+changelog_entry="$(git show origin/main:CHANGELOG.md | awk "/^## \[v${new_version}\]/{flag=1; next} /^## /{flag=0} flag")"
+
+if [[ -n "${changelog_entry}" ]]; then
+	echo -e "${changelog_entry}\n"
+else
+	abort "Unable to find changelog entry for v${new_version}. Has the prepare release PR been triggered/merged?"
+fi
+
+read -r -p "Deploy as ${new_git_tag} [y/n]? " choice
+case "${choice}" in
+	y | Y) ;;
+	n | N) exit 0 ;;
+	*) exit 1 ;;
+esac
+
+echo -e "\nCreating GitHub release..."
+gh release create "${new_git_tag}" --title "${new_git_tag}" --notes "${changelog_entry}"
 
-echo -e "\nPublishing to the buildpack registry..."
-heroku buildpacks:publish "$BP_NAME" "$newVersion"
+echo -e "\nPublishing to the Heroku Buildpack Registry..."
+heroku buildpacks:publish "${buildpack_registry_name}" "${new_git_tag}"
 echo
-heroku buildpacks:versions "${BP_NAME}" | head -n 3
+heroku buildpacks:versions "${buildpack_registry_name}" | head -n 3
diff --git a/hatchet.json b/hatchet.json
index a9f518db2..0967ef424 100644
--- a/hatchet.json
+++ b/hatchet.json
@@ -1,8 +1 @@
-{
-  "hatchet": {
-    "directory": ".hatchet/"
-  },
-  "heroku": [
-    "https://github.com/heroku/python-getting-started"
-  ]
-}
+{}
diff --git a/hatchet.lock b/hatchet.lock
index 51aa7c698..dcd024e99 100644
--- a/hatchet.lock
+++ b/hatchet.lock
@@ -1,3 +1 @@
----
-- - ".hatchet/repos/heroku/python-getting-started"
-  - main
+--- []
diff --git a/lib/build_data.sh b/lib/build_data.sh
new file mode 100644
index 000000000..856bb3df3
--- /dev/null
+++ b/lib/build_data.sh
@@ -0,0 +1,191 @@
+#!/usr/bin/env bash
+
+# This is technically redundant, since all consumers of this lib will have enabled these,
+# however, it helps Shellcheck realise the options under which these functions will run.
+set -euo pipefail
+
+BUILD_DATA_FILE="${CACHE_DIR:?}/build-data/python.json"
+PREVIOUS_BUILD_DATA_FILE="${CACHE_DIR:?}/build-data/python-prev.json"
+
+# Legacy `key=value` format file used by older Python buildpack versions.
+LEGACY_BUILD_DATA_FILE="${CACHE_DIR:?}/build-data/python"
+
+# Initializes the build data store, preserving the file from the previous build if it exists.
+# Call this at the start of `bin/compile` before using any other functions from this file.
+#
+# Usage:
+# ```
+# build_data::setup
+# ```
+function build_data::setup() {
+	if [[ -f "${BUILD_DATA_FILE}" ]]; then
+		# Rename the existing build data file rather than overwriting it, so we can lookup values
+		# from the previous build (such as when determining whether to invalidate the cache).
+		mv "${BUILD_DATA_FILE}" "${PREVIOUS_BUILD_DATA_FILE}"
+	else
+		mkdir -p "$(dirname "${BUILD_DATA_FILE}")"
+	fi
+
+	echo "{}" >"${BUILD_DATA_FILE}"
+}
+
+# Sets a string build data value. The value will be wrapped in double quotes and escaped for JSON.
+#
+# Usage:
+# ```
+# build_data::set_string "python_version" "1.2.3"
+# build_data::set_string "failure_reason" "install-dependencies::pip"
+# ```
+function build_data::set_string() {
+	local key="${1}"
+	local value="${2}"
+	build_data::_set "${key}" "${value}" "true"
+}
+
+# Sets a build data value for the elapsed time in seconds between the provided start time and the
+# current time, represented as a float with microseconds precision.
+#
+# Usage:
+# ```
+# local dependencies_install_start_time=$(build_data::current_unix_realtime)
+# # ... some operation ...
+# build_data::set_duration "dependencies_install_duration" "${dependencies_install_start_time}"
+# ```
+function build_data::set_duration() {
+	local key="${1}"
+	local start_time="${2}"
+	local end_time duration
+	end_time="$(build_data::current_unix_realtime)"
+	duration="$(awk -v start="${start_time}" -v end="${end_time}" 'BEGIN { printf "%f", (end - start) }')"
+	build_data::set_raw "${key}" "${duration}"
+}
+
+# Sets a build data value as raw JSON data. The value parameter must be valid JSON value, that's also
+# a supported Honeycomb data type (string, integer, float, or boolean only; no arrays or objects).
+# For strings, use `build_data::set_string` instead since it will handle the escaping/quoting for you.
+# And for durations, use `build_data::set_duration`.
+#
+# Usage:
+# ```
+# build_data::set_raw "python_version_outdated" "true"
+# build_data::set_raw "foo_size_mb" "42.5"
+# ```
+function build_data::set_raw() {
+	local key="${1}"
+	local value="${2}"
+	build_data::_set "${key}" "${value}" "false"
+}
+
+# Internal helper to write a key/value pair to the build data store. The buildpack shouldn't call this directly.
+# Takes a key, value, and a boolean flag indicating whether the value needs to be quoted.
+#
+# Usage:
+# ```
+# build_data::_set "foo_string" "quote me" "true"
+# build_data::_set "bar_number" "99" "false"
+# ```
+function build_data::_set() {
+	local key="${1}"
+	# Truncate the value to an arbitrary 200 characters since it will sometimes contain user-provided
+	# inputs which may be unbounded in size. Ideally individual call sites will perform more aggressive
+	# truncation themselves based on the expected value size, however this is here as a fallback.
+	# (Honeycomb supports string fields up to 64KB in size, however, it's not worth filling up the
+	# build data store or bloating the payload passed back to Vacuole/submitted to Honeycomb given the
+	# extra content in those cases is not normally useful.)
+	local value="${2:0:200}"
+	local needs_quoting="${3}"
+
+	if [[ "${needs_quoting}" == "true" ]]; then
+		# Values passed using `--arg` are treated as strings, and so have double quotes added and any JSON
+		# special characters (such as newlines, carriage returns, double quotes, backslashes) are escaped.
+		local jq_args=(--arg value "${value}")
+	else
+		# Values passed using `--argjson` are treated as raw JSON values, and so aren't escaped or quoted.
+		local jq_args=(--argjson value "${value}")
+	fi
+
+	if [[ -f "${BUILD_DATA_FILE}" ]]; then
+		local new_data_file_contents
+		new_data_file_contents="$(jq --exit-status --arg key "${key}" "${jq_args[@]}" '. + { ($key): ($value) }' "${BUILD_DATA_FILE}")"
+		echo "${new_data_file_contents}" >"${BUILD_DATA_FILE}"
+	else
+		output::error <<-EOF
+			Error: Can't find the buildpack's build data file.
+
+			The Python buildpack's internal build data file is missing:
+			${BUILD_DATA_FILE}
+
+			This file is required for the buildpack to work correctly,
+			and so you must not delete it when removing files from the
+			build cache or /tmp directories.
+		EOF
+		build_data::setup
+		build_data::set_string "failure_reason" "build-data::data-file-deleted"
+		exit 1
+	fi
+}
+
+# Check whether an entry exists in the build data store for the current build.
+# Returns zero if the key was found and non-zero otherwise.
+#
+# Usage:
+# ```
+# build_data::has "failure_reason"
+# ```
+function build_data::has() {
+	local key="${1}"
+
+	jq --exit-status --arg key "${key}" 'has($key)' "${BUILD_DATA_FILE}" >/dev/null
+}
+
+# Retrieve the value of an entry in the build data store from the previous successful build.
+# Returns the empty string if the key wasn't found in the store.
+#
+# Usage:
+# ```
+# build_data::get_previous "python_version"
+# ```
+function build_data::get_previous() {
+	local key="${1}"
+
+	# Older versions of this buildpack used a `key=value` format file instead of JSON,
+	# so we need to support this file format/location too, so older caches can be read.
+	# We check for this file first, so that we correctly handle the case where an app
+	# downgraded and then re-upgraded buildpack version, so has both files in the cache.
+	if [[ -f "${LEGACY_BUILD_DATA_FILE}" ]]; then
+		# The legacy file contains one entry per line, of form `key=value`. Entries were written in an
+		# append-only manner so there could be duplicate entries for each key, so we return only the
+		# last matching entry in the file. The empty string is returned if the key wasn't found.
+		tac "${LEGACY_BUILD_DATA_FILE}" | { grep --perl-regexp --only-matching --max-count=1 "^${key}=\K.*$" || true; }
+	elif [[ -f "${PREVIOUS_BUILD_DATA_FILE}" ]]; then
+		# By default jq will return `null` if the key isn't found, so we must handle this explicitly.
+		# We don't use `--exit-status` since `false` is a valid value for us to retrieve.
+		jq --raw-output --arg key "${key}" 'if has($key) then .[$key] else empty end' "${PREVIOUS_BUILD_DATA_FILE}"
+	fi
+}
+
+# Returns the current time since the UNIX Epoch, as a float with microseconds precision.
+#
+# Usage:
+# ```
+# local dependencies_install_start_time=$(build_data::current_unix_realtime)
+# # ... some operation ...
+# build_data::set_duration "dependencies_install_duration" "${dependencies_install_start_time}"
+# ```
+function build_data::current_unix_realtime() {
+	# We use a subshell with `LC_ALL=C` to ensure the output format isn't affected by system locale.
+	(
+		LC_ALL=C
+		echo "${EPOCHREALTIME}"
+	)
+}
+
+# Prints the contents of the build data store in sorted JSON format.
+#
+# Usage:
+# ```
+# build_data::print_bin_report_json
+# ```
+function build_data::print_bin_report_json() {
+	jq --exit-status --sort-keys '.' "${BUILD_DATA_FILE}"
+}
diff --git a/lib/cache.sh b/lib/cache.sh
new file mode 100644
index 000000000..f2103a069
--- /dev/null
+++ b/lib/cache.sh
@@ -0,0 +1,214 @@
+#!/usr/bin/env bash
+
+# This is technically redundant, since all consumers of this lib will have enabled these,
+# however, it helps Shellcheck realise the options under which these functions will run.
+set -euo pipefail
+
+# Read the full Python version of the Python install in the cache, or the empty string
+# if the cache is empty or doesn't contain a Python version metadata file.
+function cache::cached_python_full_version() {
+	local cache_dir="${1}"
+
+	if [[ -f "${cache_dir}/.heroku/python-version" ]]; then
+		local version
+		version="$(cat "${cache_dir}/.heroku/python-version")"
+		# For historical reasons the version has always been stored as `python-X.Y.Z`,
+		# so we have to remove the `python-` prefix.
+		echo "${version#python-}"
+	fi
+}
+
+# Validates and restores the contents of the build cache if appropriate.
+# The cache is discarded if any of the following have changed:
+# - Stack
+# - Python version
+# - Package manager
+# - Package manager version
+# - requirements.txt contents (pip only)
+function cache::restore() {
+	local build_dir="${1}"
+	local cache_dir="${2}"
+	local stack="${3}"
+	local cached_python_full_version="${4}"
+	local python_full_version="${5}"
+	local package_manager="${6}"
+
+	local cache_restore_start_time
+	cache_restore_start_time=$(build_data::current_unix_realtime)
+
+	if [[ ! -d "${cache_dir}/.heroku/python" ]]; then
+		build_data::set_string "cache_status" "empty"
+		build_data::set_duration "cache_restore_duration" "${cache_restore_start_time}"
+		return 0
+	fi
+
+	local cache_invalidation_reasons=()
+
+	local cached_stack
+	cached_stack="$(cat "${cache_dir}/.heroku/python-stack" || true)"
+	if [[ "${cached_stack}" != "${stack}" ]]; then
+		cache_invalidation_reasons+=("The stack has changed from ${cached_stack:-"unknown"} to ${stack}")
+	fi
+
+	if [[ "${cached_python_full_version}" != "${python_full_version}" ]]; then
+		cache_invalidation_reasons+=("The Python version has changed from ${cached_python_full_version:-"unknown"} to ${python_full_version}")
+	fi
+
+	local cached_package_manager
+	cached_package_manager="$(build_data::get_previous "package_manager")"
+	if [[ -z "${cached_package_manager}" ]]; then
+		# The build data store only exists in caches created by v252+ of the buildpack (released 2024-06-17).
+		cache_invalidation_reasons+=("The buildpack cache format has changed")
+	elif [[ "${cached_package_manager}" != "${package_manager}" ]]; then
+		cache_invalidation_reasons+=("The package manager has changed from ${cached_package_manager:-"unknown"} to ${package_manager}")
+	else
+		case "${package_manager}" in
+			pip)
+				local cached_pip_version
+				cached_pip_version="$(build_data::get_previous "pip_version")"
+				if [[ "${cached_pip_version}" != "${PIP_VERSION:?}" ]]; then
+					cache_invalidation_reasons+=("The pip version has changed from ${cached_pip_version:-"unknown"} to ${PIP_VERSION}")
+				fi
+				# We invalidate the cache if requirements.txt changes since pip is a package installer
+				# rather than a project/environment manager, and so does not deterministically manage
+				# installed Python packages. For example, if a package entry in a requirements file is
+				# later removed, pip will not uninstall the package. This check can be removed if we
+				# ever switch to only caching pip's HTTP/wheel cache rather than site-packages.
+				# TODO: Switch this to using sha256sum like the Pipenv implementation.
+				if ! cmp --silent "${cache_dir}/.heroku/requirements.txt" "${build_dir}/requirements.txt"; then
+					cache_invalidation_reasons+=("The contents of requirements.txt changed")
+				fi
+				;;
+			pipenv)
+				local cached_pipenv_version
+				cached_pipenv_version="$(build_data::get_previous "pipenv_version")"
+				if [[ "${cached_pipenv_version}" != "${PIPENV_VERSION:?}" ]]; then
+					cache_invalidation_reasons+=("The Pipenv version has changed from ${cached_pipenv_version:-"unknown"} to ${PIPENV_VERSION}")
+				fi
+				# `pipenv {install,sync}` by design don't actually uninstall packages on their own (!!):
+				# and we can't use `pipenv clean` since it isn't compatible with `--system`.
+				# https://github.com/pypa/pipenv/issues/3365
+				# We have to explicitly check for the presence of the Pipfile.lock.sha256 file,
+				# since we only started writing it to the build cache as of buildpack v292 (released 2025-07-23).
+				local pipfile_lock_checksum_file="${cache_dir}/.heroku/python/Pipfile.lock.sha256"
+				if [[ -f "${pipfile_lock_checksum_file}" ]] && ! sha256sum --check --strict --status "${pipfile_lock_checksum_file}"; then
+					cache_invalidation_reasons+=("The contents of Pipfile.lock changed")
+				fi
+				;;
+			poetry)
+				local cached_poetry_version
+				cached_poetry_version="$(build_data::get_previous "poetry_version")"
+				if [[ "${cached_poetry_version}" != "${POETRY_VERSION:?}" ]]; then
+					cache_invalidation_reasons+=("The Poetry version has changed from ${cached_poetry_version:-"unknown"} to ${POETRY_VERSION}")
+				fi
+				;;
+			uv)
+				local cached_uv_version
+				cached_uv_version="$(build_data::get_previous "uv_version")"
+				if [[ "${cached_uv_version}" != "${UV_VERSION:?}" ]]; then
+					cache_invalidation_reasons+=("The uv version has changed from ${cached_uv_version:-"unknown"} to ${UV_VERSION}")
+				fi
+				;;
+			*)
+				utils::abort_internal_error "Unhandled package manager: ${package_manager}"
+				;;
+		esac
+	fi
+
+	if [[ -f "${cache_dir}/.heroku/python/include/sqlite3.h" ]]; then
+		cache_invalidation_reasons+=("The legacy SQLite3 headers and CLI binary need to be uninstalled")
+	fi
+
+	if [[ -n "${cache_invalidation_reasons[*]}" ]]; then
+		output::step "Discarding cache since:"
+		local reason
+		for reason in "${cache_invalidation_reasons[@]}"; do
+			echo "       - ${reason}"
+		done
+
+		rm -rf \
+			"${cache_dir}/.heroku/python" \
+			"${cache_dir}/.heroku/python-poetry" \
+			"${cache_dir}/.heroku/python-stack" \
+			"${cache_dir}/.heroku/python-uv" \
+			"${cache_dir}/.heroku/python-version" \
+			"${cache_dir}/.heroku/requirements.txt"
+
+		build_data::set_string "cache_status" "discarded"
+	else
+		output::step "Restoring cache"
+		mkdir -p "${build_dir}/.heroku"
+		# Moving the files directly in place is much faster than copying when both the cache and
+		# build directory are on the same filesystem mount. The Python directory is guaranteed
+		# to not already exist thanks to the earlier `checks::existing_python_dir_present()`.
+		mv "${cache_dir}/.heroku/python" "${build_dir}/.heroku/"
+		build_data::set_string "cache_status" "reused"
+	fi
+
+	# Remove any legacy cache contents written by older buildpack versions.
+	rm -rf \
+		"${cache_dir}/build-data/python" \
+		"${cache_dir}/build-data/python-prev" \
+		"${cache_dir}/.heroku/python-sqlite3-version" \
+		"${cache_dir}/.heroku/src" \
+		"${cache_dir}/.heroku/vendor"
+
+	build_data::set_duration "cache_restore_duration" "${cache_restore_start_time}"
+}
+
+# Copies Python and dependencies from the build directory to the cache, for use by subsequent builds.
+function cache::save() {
+	local build_dir="${1}"
+	local cache_dir="${2}"
+	local stack="${3}"
+	local python_full_version="${4}"
+	local package_manager="${5}"
+
+	local cache_save_start_time
+	cache_save_start_time=$(build_data::current_unix_realtime)
+
+	output::step "Saving cache"
+
+	mkdir -p "${cache_dir}/.heroku"
+	rm -rf "${cache_dir}/.heroku/python"
+
+	local build_dir_filesystem cache_dir_filesystem
+	build_dir_filesystem="$(df --output=target "${build_dir}")"
+	cache_dir_filesystem="$(df --output=target "${cache_dir}")"
+
+	# For improved performance, we copy using hard-links if possible. This requires that the build
+	# and cache directory are on the same filesystem mount - which is the case for standard builds
+	# but not Heroku CI or build-in-app-dir. Ideally we would be able to use `--reflink=auto` here
+	# (which would avoid the need for a conditional and also mean accidental edits by users in later
+	# buildpacks to one location doesn't affect the other), however, with the current filesystems
+	# used in production benchmarking showed `--reflink=auto` was much slower than hardlinks.
+	if [[ "${build_dir_filesystem}" == "${cache_dir_filesystem}" ]]; then
+		local additional_copy_args=(--link)
+	else
+		local additional_copy_args=()
+	fi
+
+	# We must explicitly use `--no-dereference` since the default cp behaviour varies based on other
+	# options used (such as `--link`), and we don't want symlinks to be resolved since otherwise the
+	# copy will fail when copying packages that contain broken symlinks.
+	cp --recursive --no-dereference "${additional_copy_args[@]}" "${build_dir}/.heroku/python" "${cache_dir}/.heroku/"
+
+	# Metadata used by subsequent builds to determine whether the cache can be reused.
+	# These are written/consumed via separate files and not the build data store for compatibility
+	# with buildpack versions prior to the build data store existing (which was only added in v252).
+	echo "${stack}" >"${cache_dir}/.heroku/python-stack"
+	# For historical reasons the Python version was always stored with a `python-` prefix.
+	# We continue to use that format so that the file can be read by older buildpack versions.
+	echo "python-${python_full_version}" >"${cache_dir}/.heroku/python-version"
+
+	if [[ "${package_manager}" == "pip" ]]; then
+		# TODO: Switch this to using sha256sum like the Pipenv implementation.
+		cp "${build_dir}/requirements.txt" "${cache_dir}/.heroku/"
+	elif [[ "${package_manager}" == "pipenv" ]]; then
+		# This must use a relative path for the lockfile, since the output file will contain
+		# the path specified, and the build directory path changes every build.
+		sha256sum Pipfile.lock >"${cache_dir}/.heroku/python/Pipfile.lock.sha256"
+	fi
+
+	build_data::set_duration "cache_save_duration" "${cache_save_start_time}"
+}
diff --git a/lib/checks.sh b/lib/checks.sh
new file mode 100644
index 000000000..5e9e4b65e
--- /dev/null
+++ b/lib/checks.sh
@@ -0,0 +1,152 @@
+#!/usr/bin/env bash
+
+function checks::ensure_supported_stack() {
+	local stack="${1}"
+
+	case "${stack}" in
+		heroku-22 | heroku-24 | heroku-26)
+			return 0
+			;;
+		cedar* | heroku-16 | heroku-18 | heroku-20)
+			# This error will only ever be seen on non-Heroku environments, since the
+			# Heroku build system rejects builds using EOL stacks.
+			output::error <<-EOF
+				Error: The '${stack}' stack is no longer supported.
+
+				This buildpack no longer supports the '${stack}' stack since it has
+				reached its end-of-life:
+				https://devcenter.heroku.com/articles/stack#stack-support-details
+
+				Upgrade to a newer stack to continue using this buildpack.
+			EOF
+			build_data::set_string "failure_reason" "checks::stack::eol"
+			build_data::set_string "failure_detail" "${stack}"
+			exit 1
+			;;
+		*)
+			output::error <<-EOF
+				Error: The '${stack}' stack isn't recognised.
+
+				This buildpack doesn't recognise or support the '${stack}' stack.
+
+				If '${stack}' is a valid stack, make sure that you are using the latest
+				version of this buildpack and haven't pinned to an older release:
+				https://devcenter.heroku.com/articles/managing-buildpacks#view-your-buildpacks
+				https://devcenter.heroku.com/articles/managing-buildpacks#classic-buildpacks-references
+			EOF
+			build_data::set_string "failure_reason" "checks::stack::unknown"
+			build_data::set_string "failure_detail" "${stack}"
+			exit 1
+			;;
+	esac
+}
+
+function checks::duplicate_python_buildpack() {
+	local build_dir="${1}"
+
+	# The check for the `PYTHONHOME` env var prevents this warning triggering in the case
+	# where the Python install was committed to the Git repo (which will be handled later).
+	# (The env var can only have come from the `export` file of an earlier buildpack,
+	# since app provided config vars haven't been exported to the environment here.)
+	if [[ -f "${build_dir}/.heroku/python/bin/python" && -v PYTHONHOME ]]; then
+		output::error <<-EOF
+			Error: The Python buildpack has already been run this build.
+
+			An existing Python installation was found in the build directory
+			from a buildpack run earlier in the build.
+
+			This normally means there are duplicate Python buildpacks set
+			on your app, which isn't supported, can cause errors and
+			slow down builds.
+
+			Check the buildpacks set on your app and remove any duplicate
+			Python buildpack entries:
+			https://devcenter.heroku.com/articles/managing-buildpacks#view-your-buildpacks
+			https://devcenter.heroku.com/articles/managing-buildpacks#remove-classic-buildpacks
+
+			Note: This error replaces the deprecation warning which was
+			displayed in build logs starting 13th December 2024.
+		EOF
+		build_data::set_string "failure_reason" "checks::duplicate-python-buildpack"
+		exit 1
+	fi
+}
+
+function checks::existing_python_dir_present() {
+	local build_dir="${1}"
+
+	# We use `-e` here to catch the case where `python` is a file rather than a directory.
+	if [[ -e "${build_dir}/.heroku/python" ]]; then
+		output::error <<-EOF
+			Error: Existing '.heroku/python/' directory found.
+
+			Your app's source code contains an existing directory named
+			'.heroku/python/', which is where the Python buildpack needs
+			to install its files. This existing directory contains:
+
+			$(find .heroku/python/ -maxdepth 2 || true)
+
+			Writing to internal locations used by the Python buildpack
+			isn't supported and can cause unexpected errors.
+
+			If you have committed a '.heroku/python/' directory to your
+			Git repo, you must delete it or use a different location.
+
+			Otherwise, check that an earlier buildpack or 'bin/pre_compile'
+			hook hasn't created this directory.
+
+			Note: This error replaces the deprecation warning which was
+			displayed in build logs starting 13th December 2024.
+		EOF
+		build_data::set_string "failure_reason" "checks::existing-python-dir"
+		exit 1
+	fi
+}
+
+function checks::existing_venv_dir_present() {
+	local build_dir="${1}"
+	local venv_name
+
+	for venv_name in ".venv" "venv"; do
+		if [[ -f "${build_dir}/${venv_name}/pyvenv.cfg" ]]; then
+			output::error <<-EOF
+				Error: Existing '${venv_name}/' directory found.
+
+				Your app's source code contains an existing directory named
+				'${venv_name}/', which looks like a Python virtual environment:
+
+				$(find "${venv_name}/" -maxdepth 2 | sort || true)
+
+				Including a virtual environment directory in your app source
+				isn't supported since the files within it are specific to a
+				single machine and so won't work when run somewhere else.
+
+				If you've committed a '${venv_name}/' directory to your Git repo, you
+				must delete it and add the directory to your .gitignore file.
+
+				To do this:
+				1. Run 'git rm --cached -r ${venv_name}/' to remove the directory
+				   from the Git index.
+				2. Create a '.gitignore' file in the root of your repository
+				   if it doesn't already exist.
+				3. Add the '${venv_name}/' directory to the .gitignore file as a
+				   new entry on its own line (don't include the quotes).
+				4. Stage the change using 'git add .gitignore' and then
+				   'git commit' all changes.
+
+				For more information, see:
+				https://docs.github.com/en/get-started/git-basics/ignoring-files
+
+				If the directory was created by a 'bin/pre_compile' hook or
+				an earlier buildpack, you must instead update them to create
+				the virtual environment in a different location.
+
+				Note: This error replaces the previous warning which had been
+				displayed in build logs since 2nd September 2025.
+			EOF
+			build_data::set_string "failure_reason" "checks::existing-venv-dir"
+			build_data::set_string "failure_detail" "${venv_name}"
+			exit 1
+		fi
+	done
+}
diff --git a/lib/hooks.sh b/lib/hooks.sh
new file mode 100644
index 000000000..b99dc4950
--- /dev/null
+++ b/lib/hooks.sh
@@ -0,0 +1,41 @@
+#!/usr/bin/env bash
+
+# This is technically redundant, since all consumers of this lib will have enabled these,
+# however, it helps Shellcheck realise the options under which these functions will run.
+set -euo pipefail
+
+# Used to run the `bin/pre_compile` and `bin/post_compile` scripts if found in the app source,
+# allowing for build customisation.
+function hooks::run_hook() {
+	local hook_name="${1}"
+	local script_path="bin/${hook_name}"
+
+	if [[ -f "${script_path}" ]]; then
+		local hook_start_time
+		hook_start_time=$(build_data::current_unix_realtime)
+		output::step "Running ${script_path} hook"
+		build_data::set_raw "${hook_name}_hook" "true"
+		chmod +x "${script_path}"
+
+		# shellcheck disable=SC2310 # This function is invoked in an 'if' condition so set -e will be disabled.
+		if ! sub_env "${script_path}" |& output::indent; then
+			output::error <<-EOF
+				Error: Failed to run the ${script_path} script.
+
+				We found a '${script_path}' script in your app source, so ran
+				it to allow for customisation of the build process.
+
+				However, this script exited with a non-zero exit status.
+
+				Fix any errors output by your script above, or remove/rename
+				the script to prevent it from being run during the build.
+			EOF
+			build_data::set_string "failure_reason" "hooks::${hook_name}"
+			exit 1
+		fi
+
+		build_data::set_duration "${hook_name}_hook_duration" "${hook_start_time}"
+	else
+		build_data::set_raw "${hook_name}_hook" "false"
+	fi
+}
diff --git a/lib/kvstore.sh b/lib/kvstore.sh
deleted file mode 100644
index bd5c6fad0..000000000
--- a/lib/kvstore.sh
+++ /dev/null
@@ -1,75 +0,0 @@
-#!/usr/bin/env bash
-
-# Taken from: https://github.com/heroku/heroku-buildpack-nodejs/blob/main/lib/kvstore.sh
-
-kv_create() {
-  local f="${1}"
-  mkdir -p "$(dirname "${f}")"
-  touch "${f}"
-}
-
-kv_clear() {
-  local f="${1}"
-  echo "" >"${f}"
-}
-
-kv_set() {
-  if [[ $# -eq 3 ]]; then
-    local f="${1}"
-    if [[ -f "${f}" ]]; then
-      echo "${2}=${3}" >>"${f}"
-    fi
-  fi
-}
-
-kv_get() {
-  if [[ $# -eq 2 ]]; then
-    local f="${1}"
-    if [[ -f "${f}" ]]; then
-      grep "^${2}=" "${f}" | sed -e "s/^${2}=//" | tail -n 1
-    fi
-  fi
-}
-
-# get the value, but wrap it in quotes if it contains a space
-kv_get_escaped() {
-  local value
-  value=$(kv_get "${1}" "${2}")
-  if [[ "${value}" =~ [[:space:]]+ ]]; then
-    echo "\"${value}\""
-  else
-    echo "${value}"
-  fi
-}
-
-kv_keys() {
-  local f="${1}"
-  local keys=()
-
-  if [[ -f "${f}" ]]; then
-    # Iterate over each line, splitting on the '=' character
-    #
-    # The || [[ -n "${key}" ]] statement addresses an issue with reading the last line
-    # of a file when there is no newline at the end. This will not happen if the file
-    # is created with this module, but can happen if it is written by hand.
-    # See: https://stackoverflow.com/questions/12916352/shell-script-read-missing-last-line
-    while IFS="=" read -r key value || [[ -n "${key}" ]]; do
-      # if there are any empty lines in the store, skip them
-      if [[ -n "${key}" ]]; then
-        keys+=("${key}")
-      fi
-    done <"${f}"
-
-    echo "${keys[@]}" | tr ' ' '\n' | sort -u
-  fi
-}
-
-kv_list() {
-  local f="${1}"
-
-  kv_keys "${f}" | tr ' ' '\n' | while read -r key; do
-    if [[ -n "${key}" ]]; then
-      echo "${key}=$(kv_get_escaped "${f}" "${key}")"
-    fi
-  done
-}
diff --git a/lib/metadata.sh b/lib/metadata.sh
deleted file mode 100644
index 20aab3da3..000000000
--- a/lib/metadata.sh
+++ /dev/null
@@ -1,72 +0,0 @@
-#!/usr/bin/env bash
-
-# Based on: https://github.com/heroku/heroku-buildpack-nodejs/blob/main/lib/metadata.sh
-
-source "${BUILDPACK_DIR}/lib/kvstore.sh"
-
-# Variables shared by this whole module
-BUILD_DATA_FILE=""
-PREVIOUS_BUILD_DATA_FILE=""
-
-# Must be called before you can use any other methods
-meta_init() {
-  local cache_dir="${1}"
-  local buildpack_name="${2}"
-  BUILD_DATA_FILE="${cache_dir}/build-data/${buildpack_name}"
-  PREVIOUS_BUILD_DATA_FILE="${cache_dir}/build-data/${buildpack_name}-prev"
-}
-
-# Moves the data from the last build into the correct place, and clears the store
-# This should be called after meta_init in bin/compile
-meta_setup() {
-  # if the file already exists because it's from the last build, save it
-  if [[ -f "${BUILD_DATA_FILE}" ]]; then
-    cp "${BUILD_DATA_FILE}" "${PREVIOUS_BUILD_DATA_FILE}"
-  fi
-
-  kv_create "${BUILD_DATA_FILE}"
-  kv_clear "${BUILD_DATA_FILE}"
-}
-
-# Force removal of exiting data file state. This is mostly useful during testing and not
-# expected to be used during buildpack execution.
-meta_force_clear() {
-  [[ -f "${BUILD_DATA_FILE}" ]] && rm "${BUILD_DATA_FILE}"
-  [[ -f "${PREVIOUS_BUILD_DATA_FILE}" ]] && rm "${PREVIOUS_BUILD_DATA_FILE}"
-}
-
-meta_get() {
-  kv_get "${BUILD_DATA_FILE}" "${1}"
-}
-
-meta_set() {
-  kv_set "${BUILD_DATA_FILE}" "${1}" "${2}"
-}
-
-# Similar to mtime from buildpack-stdlib
-meta_time() {
-  local key="${1}"
-  local start="${2}"
-  local end="${3:-$(nowms)}"
-  local time
-  time="$(echo "${start}" "${end}" | awk '{ printf "%.3f", ($2 - $1)/1000 }')"
-  kv_set "${BUILD_DATA_FILE}" "${key}" "${time}"
-}
-
-# Retrieve a value from a previous build if it exists
-# This is useful to give the user context about what changed if the
-# build has failed. Ex:
-#   - changed stacks
-#   - deployed with a new major version of Node
-#   - etc
-meta_prev_get() {
-  kv_get "${PREVIOUS_BUILD_DATA_FILE}" "${1}"
-}
-
-log_meta_data() {
-  # print all values on one line in logfmt format
-  # https://brandur.org/logfmt
-  # the echo call ensures that all values are printed on a single line
-  # shellcheck disable=SC2005 disable=SC2046
-  echo $(kv_list "${BUILD_DATA_FILE}")
-}
diff --git a/lib/output.sh b/lib/output.sh
new file mode 100644
index 000000000..1f6dda760
--- /dev/null
+++ b/lib/output.sh
@@ -0,0 +1,78 @@
+#!/usr/bin/env bash
+
+# This is technically redundant, since all consumers of this lib will have enabled these,
+# however, it helps Shellcheck realise the options under which these functions will run.
+set -euo pipefail
+
+ANSI_BLUE=$'\e[1;34m'
+ANSI_RED=$'\e[1;31m'
+ANSI_YELLOW=$'\e[1;33m'
+ANSI_RESET=$'\e[0m'
+
+# Output a single line step message to stdout.
+#
+# Usage:
+# ```
+# output::step "Installing Python ..."
+# ```
+function output::step() {
+	echo "-----> ${1}"
+}
+
+# Indent passed stdout. Typically used to indent command output within a step.
+#
+# Usage:
+# ```
+# pip install ... |& output::indent
+# ```
+function output::indent() {
+	sed --unbuffered "s/^/       /"
+}
+
+# Output a styled multi-line notice message to stderr.
+#
+# Usage:
+# ```
+# output::notice <<-EOF
+# 	Note: The note summary.
+#
+# 	Detailed description.
+# EOF
+# ```
+function output::notice() {
+	echo >&2
+	sed --expression "s/^/${ANSI_BLUE} !     /" --expression "s/$/${ANSI_RESET}/" >&2
+	echo >&2
+}
+
+# Output a styled multi-line warning message to stderr.
+#
+# Usage:
+# ```
+# output::warning <<-EOF
+# 	Warning: The warning summary.
+#
+# 	Detailed description.
+# EOF
+# ```
+function output::warning() {
+	echo >&2
+	sed --expression "s/^/${ANSI_YELLOW} !     /" --expression "s/$/${ANSI_RESET}/" >&2
+	echo >&2
+}
+
+# Output a styled multi-line error message to stderr.
+#
+# Usage:
+# ```
+# output::error <<-EOF
+# 	Error: The error summary.
+#
+# 	Detailed description.
+# EOF
+# ```
+function output::error() {
+	echo >&2
+	sed --expression "s/^/${ANSI_RED} !     /" --expression "s/$/${ANSI_RESET}/" >&2
+	echo >&2
+}
diff --git a/lib/package_manager.sh b/lib/package_manager.sh
new file mode 100644
index 000000000..95c4868b6
--- /dev/null
+++ b/lib/package_manager.sh
@@ -0,0 +1,164 @@
+#!/usr/bin/env bash
+
+# This is technically redundant, since all consumers of this lib will have enabled these,
+# however, it helps Shellcheck realise the options under which these functions will run.
+set -euo pipefail
+
+function package_manager::determine_package_manager() {
+	local build_dir="${1}"
+	local package_managers_found=()
+	local package_managers_found_display_text=()
+
+	if [[ -f "${build_dir}/Pipfile.lock" ]]; then
+		package_managers_found+=(pipenv)
+		package_managers_found_display_text+=("Pipfile.lock (Pipenv)")
+	elif [[ -f "${build_dir}/Pipfile" ]]; then
+		output::error <<-'EOF'
+			Error: No 'Pipfile.lock' found!
+
+			A 'Pipfile' file was found, however, the associated 'Pipfile.lock'
+			Pipenv lockfile wasn't. This means your app dependency versions
+			aren't pinned, which means the package versions used on Heroku
+			might not match those installed in other environments.
+
+			Using Pipenv in this way is unsafe and no longer supported.
+
+			Run 'pipenv lock' locally to generate the lockfile, and make sure
+			that 'Pipfile.lock' isn't listed in '.gitignore' or '.slugignore'.
+
+			Alternatively, if you wish to switch to another package manager,
+			delete your 'Pipfile' and then add either a 'requirements.txt',
+			'poetry.lock' or 'uv.lock' file.
+
+			If you aren't sure which package manager to use, we recommend
+			trying uv, since it supports lockfiles, is extremely fast, and
+			is actively maintained by a full-time team:
+			https://docs.astral.sh/uv/
+		EOF
+		build_data::set_string "failure_reason" "package-manager::pipenv-missing-lockfile"
+		exit 1
+	fi
+
+	if [[ -f "${build_dir}/requirements.txt" ]]; then
+		package_managers_found+=(pip)
+		package_managers_found_display_text+=("requirements.txt (pip)")
+	fi
+
+	if [[ -f "${build_dir}/poetry.lock" ]]; then
+		package_managers_found+=(poetry)
+		package_managers_found_display_text+=("poetry.lock (Poetry)")
+	fi
+
+	if [[ -f "${build_dir}/uv.lock" ]]; then
+		package_managers_found+=(uv)
+		package_managers_found_display_text+=("uv.lock (uv)")
+	fi
+
+	local num_package_managers_found=${#package_managers_found[@]}
+
+	case "${num_package_managers_found}" in
+		1)
+			echo "${package_managers_found[0]}"
+			return 0
+			;;
+		0)
+			if [[ -f "${build_dir}/setup.py" ]]; then
+				output::error <<-EOF
+					Error: Implicit setup.py file support has been sunset.
+
+					Your app currently only has a setup.py file and no Python
+					package manager files. This means that the buildpack can't
+					tell which package manager you want to use, and whether to
+					install your project in editable mode or not.
+
+					Previously the buildpack guessed and used pip to install your
+					dependencies in editable mode. However, this fallback was
+					deprecated in September 2025 and has now been sunset.
+
+					You must now add an explicit package manager file to your app,
+					such as a requirements.txt, poetry.lock or uv.lock file.
+
+					To continue using your setup.py file with pip in editable
+					mode, create a new file in the root directory of your app
+					named 'requirements.txt' containing the requirement
+					'--editable .' (without quotes).
+
+					Alternatively, if you wish to switch to another package
+					manager, we recommend uv, since it supports lockfiles, is
+					faster, and is actively maintained by a full-time team:
+					https://docs.astral.sh/uv/
+				EOF
+				build_data::set_string "failure_reason" "package-manager::setup-py-only"
+				exit 1
+			fi
+
+			output::error <<-EOF
+				Error: Couldn't find any supported Python package manager files.
+
+				A Python app on Heroku must have either a 'requirements.txt',
+				'Pipfile.lock', 'poetry.lock' or 'uv.lock' package manager file
+				in the root directory of its source code.
+
+				Currently the root directory of your app contains:
+
+				$(ls -1A --indicator-style=slash "${build_dir}" || true)
+
+				If your app already has a package manager file, check that it:
+
+				1. Is in the top level directory (not a subdirectory).
+				2. Has the correct spelling (the filenames are case-sensitive).
+				3. Isn't listed in '.gitignore' or '.slugignore'.
+				4. Has been added to the Git repository using 'git add --all'
+				   and then committed using 'git commit'.
+
+				Otherwise, add a package manager file to your app. If your app has
+				no dependencies, then create an empty 'requirements.txt' file.
+
+				If you aren't sure which package manager to use, we recommend
+				trying uv, since it supports lockfiles, is extremely fast, and
+				is actively maintained by a full-time team:
+				https://docs.astral.sh/uv/
+
+				For help with using Python on Heroku, see:
+				https://devcenter.heroku.com/articles/getting-started-with-python
+				https://devcenter.heroku.com/articles/python-support
+			EOF
+			build_data::set_string "failure_reason" "package-manager::none-found"
+			exit 1
+			;;
+		*)
+			output::error <<-EOF
+				Error: Multiple Python package manager files were found.
+
+				Exactly one package manager file should be present in your app's
+				source code, however, several were found:
+
+				$(printf -- "%s\n" "${package_managers_found_display_text[@]}")
+
+				Previously, the buildpack guessed which package manager to use
+				and installed your dependencies with the first package manager
+				listed above. However, this implicit behaviour was deprecated
+				in November 2024 and is now no longer supported.
+
+				You must decide which package manager you want to use with your
+				app, and then delete the file(s) and any config from the others.
+
+				If you aren't sure which package manager to use, we recommend
+				trying uv, since it supports lockfiles, is extremely fast, and
+				is actively maintained by a full-time team:
+				https://docs.astral.sh/uv/
+
+				Note: If you use a third-party uv or Poetry buildpack, you must
+				remove it from your app, since it's no longer required and the
+				requirements.txt file it generates will trigger this error. See:
+				https://devcenter.heroku.com/articles/managing-buildpacks#remove-classic-buildpacks
+			EOF
+			build_data::set_string "failure_reason" "package-manager::multiple-found"
+			build_data::set_string "failure_detail" "$(
+				IFS=,
+				echo "${package_managers_found[*]}"
+			)"
+			exit 1
+			;;
+	esac
+}
diff --git a/lib/pip.sh b/lib/pip.sh
new file mode 100644
index 000000000..479ad5e32
--- /dev/null
+++ b/lib/pip.sh
@@ -0,0 +1,152 @@
+#!/usr/bin/env bash
+
+# This is technically redundant, since all consumers of this lib will have enabled these,
+# however, it helps Shellcheck realise the options under which these functions will run.
+set -euo pipefail
+
+PIP_VERSION=$(utils::get_requirement_version 'pip')
+# This is hardcoded rather than managed by Dependabot since we can't update to newer versions due to:
+# https://github.com/heroku/heroku-buildpack-python/pull/1630#issuecomment-2324236653
+# Also, once we drop support for older Pythons we'll stop installing setuptools entirely.
+SETUPTOOLS_VERSION='70.3.0'
+
+function pip::install_pip() {
+	local python_home="${1}"
+	local python_major_version="${2}"
+	local export_file="${3}"
+	local profile_d_file="${4}"
+
+	build_data::set_string "pip_version" "${PIP_VERSION}"
+
+	local packages_to_install=(
+		"pip==${PIP_VERSION}"
+	)
+	local packages_display_text="pip ${PIP_VERSION}"
+
+	# We only install setuptools on Python 3.12 and older, since:
+	# - pip now uses isolated build environments into which it installs setuptools and wheel
+	#   if needed when installing packages from an sdist.
+	# - Most of the Python ecosystem has stopped installing them for Python 3.12+ already.
+	# See the Python CNB's removal for more details: https://github.com/heroku/buildpacks-python/pull/243
+	if [[ "${python_major_version}" == +(3.10|3.11|3.12) ]]; then
+		build_data::set_string "setuptools_version" "${SETUPTOOLS_VERSION}"
+		packages_to_install+=(
+			"setuptools==${SETUPTOOLS_VERSION}"
+		)
+		packages_display_text+=" and setuptools ${SETUPTOOLS_VERSION}"
+	fi
+
+	# Note: We still perform this install step even if the cache was reused, since we have no guarantee
+	# that the cached package versions are correct (different versions could have been specified in the
+	# app's requirements.txt in the last build). The install will be a no-op if the versions match.
+	output::step "Installing ${packages_display_text}"
+
+	# We use the pip wheel bundled within Python's standard library to install our chosen
+	# pip version, since it's faster than `ensurepip` followed by an upgrade in place.
+	local bundled_pip_module_path
+	bundled_pip_module_path="$(utils::bundled_pip_module_path "${python_home}" "${python_major_version}")"
+
+	# `--isolated`: Prevents any custom pip configuration added by third party buildpacks (via env
+	#               vars or global config files) from breaking package manager bootstrapping.
+	# shellcheck disable=SC2310 # This function is invoked in an 'if' condition so set -e will be disabled.
+	if ! {
+		python "${bundled_pip_module_path}" \
+			install \
+			--disable-pip-version-check \
+			--isolated \
+			--no-cache-dir \
+			--no-input \
+			--quiet \
+			"${packages_to_install[@]}" \
+			|& output::indent
+	}; then
+		output::error <<-EOF
+			Error: Unable to install pip.
+
+			In some cases, this happens due to a temporary issue with
+			the network connection or Python Package Index (PyPI).
+
+			Try building again to see if the error resolves itself.
+
+			If that doesn't help, check the status of PyPI here:
+			https://status.python.org
+		EOF
+		build_data::set_string "failure_reason" "install-package-manager::pip"
+		exit 1
+	fi
+
+	# Saves us having to pass `--disable-pip-version-check` each time pip is used. Note: We can't use
+	# this for the pip install usage above, since `--isolated` disables reading of `PIP_` env vars.
+	export PIP_DISABLE_PIP_VERSION_CHECK="1"
+
+	# Set the same env vars in the environment used by later buildpacks.
+	cat >>"${export_file}" <<-EOF
+		export PIP_DISABLE_PIP_VERSION_CHECK="1"
+	EOF
+
+	# And the environment used at app run-time.
+	cat >>"${profile_d_file}" <<-EOF
+		export PIP_DISABLE_PIP_VERSION_CHECK="1"
+	EOF
+}
+
+function pip::install_dependencies() {
+	# Make select pip config vars set on the Heroku app available to pip.
+	# TODO: Expose all config vars (after suitable checks are added for unsafe env vars)
+	# to allow for the env var interpolation feature of requirements files to work.
+	#
+	# PIP_EXTRA_INDEX_URL allows for an alternate pypi URL to be used.
+	# shellcheck disable=SC2154 # TODO: Env var is referenced but not assigned.
+	if [[ -r "${ENV_DIR}/PIP_EXTRA_INDEX_URL" ]]; then
+		PIP_EXTRA_INDEX_URL="$(cat "${ENV_DIR}/PIP_EXTRA_INDEX_URL")"
+		export PIP_EXTRA_INDEX_URL
+	fi
+
+	local pip_install_command=(
+		pip
+		install
+		-r requirements.txt
+	)
+
+	# Install test dependencies too when the buildpack is invoked via `bin/test-compile` on Heroku CI.
+	# We install both requirements files at the same time to allow pip to resolve version conflicts.
+	if [[ -v INSTALL_TEST && -f requirements-test.txt ]]; then
+		pip_install_command+=(-r requirements-test.txt)
+	fi
+
+	# We only display the most relevant command args here, to improve the signal to noise ratio.
+	output::step "Installing dependencies using '${pip_install_command[*]}'"
+
+	local install_log
+	install_log=$(mktemp)
+
+	# The sed usage is to reduce the verbosity of output lines like:
+	# ...when using Python 3.10 and older:
+	# "Requirement already satisfied: typing-extensions==4.15.0 in ./.heroku/python/lib/python3.10/site-packages (from -r requirements.txt (line 2)) (4.15.0)"
+	# ...when using Python 3.11+:
+	# "Requirement already satisfied: typing-extensions==4.15.0 in /app/.heroku/python/lib/python3.14/site-packages (from -r requirements.txt (line 5)) (4.15.0)"
+	# shellcheck disable=SC2310 # This function is invoked in an 'if' condition so set -e will be disabled.
+	if ! {
+		"${pip_install_command[@]}" \
+			--exists-action=w \
+			--no-cache-dir \
+			--no-input \
+			--progress-bar off \
+			--src='/app/.heroku/python/src' \
+			|& tee "${install_log}" \
+			|& sed --unbuffered --regexp-extended \
+				--expression 's# in (/app|\.)/\.heroku/python/lib/python[0-9.]+/site-packages##' \
+			|& output::indent
+	}; then
+		# TODO: Overhaul warnings and combine them with error handling.
+		show-warnings "${install_log}"
+
+		output::error <<-EOF
+			Error: Unable to install dependencies using pip.
+
+			See the log output above for more information.
+		EOF
+		build_data::set_string "failure_reason" "install-dependencies::pip"
+		exit 1
+	fi
+}
diff --git a/lib/pipenv.sh b/lib/pipenv.sh
new file mode 100644
index 000000000..073f00e87
--- /dev/null
+++ b/lib/pipenv.sh
@@ -0,0 +1,169 @@
+#!/usr/bin/env bash
+
+# This is technically redundant, since all consumers of this lib will have enabled these,
+# however, it helps Shellcheck realise the options under which these functions will run.
+set -euo pipefail
+
+PIPENV_VERSION=$(utils::get_requirement_version 'pipenv')
+
+function pipenv::install_pipenv() {
+	local python_home="${1}"
+	local python_major_version="${2}"
+	local export_file="${3}"
+	local profile_d_file="${4}"
+
+	# Ideally we would only make Pipenv available during the build to reduce slug size, however,
+	# the buildpack has historically not done that and so some apps are relying on it at run-time
+	# (for example via `pipenv run` commands in their Procfile). As such, we have to store it in
+	# the build directory, but must do so via the symlinked `/app/.heroku/python` path so the
+	# venv doesn't break when the build directory is relocated to /app at run-time.
+	local pipenv_root="${python_home}/pipenv"
+
+	# We nest the venv and then symlink the `pipenv` script to prevent the rest of `venv/bin/`
+	# (such as entrypoint scripts from Pipenv's dependencies, or the venv's activation scripts)
+	# from being added to PATH and exposed to the app.
+	local pipenv_bin_dir="${pipenv_root}/bin"
+	local pipenv_venv_dir="${pipenv_root}/venv"
+
+	build_data::set_string "pipenv_version" "${PIPENV_VERSION}"
+
+	# The earlier buildpack cache invalidation step will have already handled the case where the
+	# Pipenv version has changed, so here we only need to check that a Pipenv install exists.
+	# Note: We don't need to use the `-e` trick of `install_poetry()` since we're installing into
+	# a constant path, rather than the cache directory (which can change location).
+	if [[ -f "${pipenv_bin_dir}/pipenv" ]]; then
+		output::step "Using cached Pipenv ${PIPENV_VERSION}"
+	else
+		output::step "Installing Pipenv ${PIPENV_VERSION}"
+
+		mkdir -p "${pipenv_root}"
+
+		# We use the pip wheel bundled within Python's standard library to install Pipenv,
+		# since Pipenv vendors its own pip, so doesn't need an install in the venv.
+		python -m venv --without-pip "${pipenv_venv_dir}"
+
+		local bundled_pip_module_path
+		bundled_pip_module_path="$(utils::bundled_pip_module_path "${python_home}" "${python_major_version}")"
+
+		# `--isolated`: Prevents any custom pip configuration added by third party buildpacks (via env
+		#               vars or global config files) from breaking package manager bootstrapping.
+		# shellcheck disable=SC2310 # This function is invoked in an 'if' condition so set -e will be disabled.
+		if ! {
+			"${pipenv_venv_dir}/bin/python" "${bundled_pip_module_path}" \
+				install \
+				--disable-pip-version-check \
+				--isolated \
+				--no-cache-dir \
+				--no-input \
+				--quiet \
+				"pipenv==${PIPENV_VERSION}" \
+				|& output::indent
+		}; then
+			output::error <<-EOF
+				Error: Unable to install Pipenv.
+
+				In some cases, this happens due to a temporary issue with
+				the network connection or Python Package Index (PyPI).
+
+				Try building again to see if the error resolves itself.
+
+				If that doesn't help, check the status of PyPI here:
+				https://status.python.org
+			EOF
+			build_data::set_string "failure_reason" "install-package-manager::pipenv"
+			exit 1
+		fi
+
+		mkdir -p "${pipenv_bin_dir}"
+		ln --symbolic --no-target-directory "${pipenv_venv_dir}/bin/pipenv" "${pipenv_bin_dir}/pipenv"
+	fi
+
+	export PATH="${pipenv_bin_dir}:${PATH}"
+	# Force Pipenv to manage the system Python site-packages instead of using venvs.
+	export PIPENV_SYSTEM="1"
+	# Hide Pipenv's notice about finding/using an existing virtual environment.
+	export PIPENV_VERBOSITY="-1"
+	# Work around a Pipenv bug when using `--system`, whereby it doesn't correctly install dependencies
+	# that happen to also be a dependency of Pipenv (such as `certifi` and `packaging`). In general
+	# Pipenv's support for its `--system` mode is very buggy. Longer term we should explore moving
+	# to venvs, however, that will need to be coordinated across all package managers and will also
+	# change paths for Python which could break other use cases. Be careful removing this even if the
+	# `pip_basic` test that installs certifi/packaging still passes, since the repro seems to depend
+	# on specific package version combinations / other factors and so the testcase is very fragile.
+	export VIRTUAL_ENV="${python_home}"
+
+	# Set the same env vars in the environment used by later buildpacks.
+	cat >>"${export_file}" <<-EOF
+		export PATH="${pipenv_bin_dir}:\${PATH}"
+		export PIPENV_SYSTEM="1"
+		export PIPENV_VERBOSITY="-1"
+		export VIRTUAL_ENV="${python_home}"
+	EOF
+
+	# And the environment used at app run-time.
+	cat >>"${profile_d_file}" <<-EOF
+		export PATH="${pipenv_bin_dir}:\${PATH}"
+		export PIPENV_SYSTEM="1"
+		export PIPENV_VERBOSITY="-1"
+		export VIRTUAL_ENV="${python_home}"
+	EOF
+}
+
+# Previous versions of the buildpack used to cache the checksum of the lockfile to allow
+# for skipping pipenv install if the lockfile was unchanged. However, this is not always safe
+# to do (the lockfile can refer to dependencies that can change independently of the lockfile,
+# for example, when using a local non-editable file dependency), so we no longer ever skip
+# install, and instead defer to Pipenv to determine whether install is actually a no-op.
+function pipenv::install_dependencies() {
+	# Make select pip config vars set on the Heroku app available to the pip used by Pipenv.
+	# TODO: Expose all config vars (after suitable checks are added for unsafe env vars).
+	#
+	# PIP_EXTRA_INDEX_URL allows for an alternate pypi URL to be used.
+	# shellcheck disable=SC2154 # TODO: Env var is referenced but not assigned.
+	if [[ -r "${ENV_DIR}/PIP_EXTRA_INDEX_URL" ]]; then
+		PIP_EXTRA_INDEX_URL="$(cat "${ENV_DIR}/PIP_EXTRA_INDEX_URL")"
+		export PIP_EXTRA_INDEX_URL
+	fi
+
+	# Note: We can't use `pipenv sync` since it doesn't support `--deploy` and so won't abort
+	# if the lockfile is out of date.
+	local pipenv_install_command=(
+		pipenv
+		install
+		--deploy
+	)
+
+	# Install test dependencies too when the buildpack is invoked via `bin/test-compile` on Heroku CI.
+	if [[ -v INSTALL_TEST ]]; then
+		pipenv_install_command+=(--dev)
+	fi
+
+	# We only display the most relevant command args here, to improve the signal to noise ratio.
+	output::step "Installing dependencies using '${pipenv_install_command[*]}'"
+
+	local install_log
+	install_log=$(mktemp)
+
+	# TODO: Expose app config vars to the install command as part of doing so for all package managers.
+	# `PIPENV_NOSPIN`: Disable progress spinners.
+	# `PIP_SRC`: Override the editable VCS repo location from its default of inside the build directory
+	#            (Pipenv uses pip internally, and doesn't offer its own config option for this).
+	# shellcheck disable=SC2310 # This function is invoked in an 'if' condition so set -e will be disabled.
+	if ! {
+		PIPENV_NOSPIN="1" PIP_SRC="/app/.heroku/python/src" \
+			"${pipenv_install_command[@]}" \
+			|& tee "${install_log}" \
+			|& output::indent
+	}; then
+		# TODO: Overhaul warnings and combine them with error handling.
+		show-warnings "${install_log}"
+
+		output::error <<-EOF
+			Error: Unable to install dependencies using Pipenv.
+
+			See the log output above for more information.
+		EOF
+		build_data::set_string "failure_reason" "install-dependencies::pipenv"
+		exit 1
+	fi
+}
diff --git a/lib/poetry.sh b/lib/poetry.sh
new file mode 100644
index 000000000..507185b03
--- /dev/null
+++ b/lib/poetry.sh
@@ -0,0 +1,157 @@
+#!/usr/bin/env bash
+
+# This is technically redundant, since all consumers of this lib will have enabled these,
+# however, it helps Shellcheck realise the options under which these functions will run.
+set -euo pipefail
+
+POETRY_VERSION=$(utils::get_requirement_version 'poetry')
+
+function poetry::install_poetry() {
+	local python_home="${1}"
+	local python_major_version="${2}"
+	local cache_dir="${3}"
+	local export_file="${4}"
+
+	# We store Poetry in the build cache, since we only need it during the build.
+	local poetry_root="${cache_dir}/.heroku/python-poetry"
+
+	# We nest the venv and then symlink the `poetry` script to prevent the rest of `venv/bin/`
+	# (such as entrypoint scripts from Poetry's dependencies, or the venv's activation scripts)
+	# from being added to PATH and exposed to the app.
+	local poetry_bin_dir="${poetry_root}/bin"
+	local poetry_venv_dir="${poetry_root}/venv"
+
+	build_data::set_string "poetry_version" "${POETRY_VERSION}"
+
+	# The earlier buildpack cache invalidation step will have already handled the case where the
+	# Poetry version has changed, so here we only need to check that a valid Poetry install exists.
+	# venvs are not relocatable, so if the cache directory were ever to change location, the cached
+	# Poetry installation would stop working. To save having to track the cache location via build
+	# metadata, we instead rely on the fact that relocating the venv would also break the absolute
+	# path `poetry` symlink created below, and that the `-e` condition not only checks that the
+	# `poetry` symlink exists, but that its target is also valid.
+	# Note: Whilst the Codon cache location remains stable from build to build, for Heroku CI the
+	# cache directory currently does not, so the cached Poetry will always be invalidated there.
+	if [[ -e "${poetry_bin_dir}/poetry" ]]; then
+		output::step "Using cached Poetry ${POETRY_VERSION}"
+	else
+		output::step "Installing Poetry ${POETRY_VERSION}"
+
+		# The Poetry directory will already exist in the relocated cache case mentioned above.
+		rm -rf "${poetry_root}"
+		mkdir -p "${poetry_root}"
+
+		# We use the pip wheel bundled within Python's standard library to install Poetry.
+		# Whilst Poetry does still require pip for some tasks (such as package uninstalls),
+		# it bundles its own copy for use as a fallback. As such we don't need to install pip
+		# into the Poetry venv (and in fact, Poetry wouldn't use this install anyway, since
+		# it only finds an external pip if it exists in the target venv).
+		python -m venv --without-pip "${poetry_venv_dir}"
+
+		local bundled_pip_module_path
+		bundled_pip_module_path="$(utils::bundled_pip_module_path "${python_home}" "${python_major_version}")"
+
+		# `--isolated`: Prevents any custom pip configuration added by third party buildpacks (via env
+		#               vars or global config files) from breaking package manager bootstrapping.
+		# shellcheck disable=SC2310 # This function is invoked in an 'if' condition so set -e will be disabled.
+		if ! {
+			"${poetry_venv_dir}/bin/python" "${bundled_pip_module_path}" \
+				install \
+				--disable-pip-version-check \
+				--isolated \
+				--no-cache-dir \
+				--no-input \
+				--quiet \
+				"poetry==${POETRY_VERSION}" \
+				|& output::indent
+		}; then
+			output::error <<-EOF
+				Error: Unable to install Poetry.
+
+				In some cases, this happens due to a temporary issue with
+				the network connection or Python Package Index (PyPI).
+
+				Try building again to see if the error resolves itself.
+
+				If that doesn't help, check the status of PyPI here:
+				https://status.python.org
+			EOF
+			build_data::set_string "failure_reason" "install-package-manager::poetry"
+			exit 1
+		fi
+
+		mkdir -p "${poetry_bin_dir}"
+		# NB: This symlink must not use `--relative`, since we want the symlink to break if the cache
+		# (and thus venv) were ever relocated - so that it triggers a reinstall (see above).
+		ln --symbolic --no-target-directory "${poetry_venv_dir}/bin/poetry" "${poetry_bin_dir}/poetry"
+	fi
+
+	export PATH="${poetry_bin_dir}:${PATH}"
+	# Force Poetry to manage the system Python site-packages instead of using venvs.
+	export POETRY_VIRTUALENVS_CREATE="false"
+	# Force Poetry to use our Python rather than scanning PATH (which might pick system Python).
+	# Though this currently doesn't work as documented: https://github.com/python-poetry/poetry/issues/10226
+	export POETRY_VIRTUALENVS_USE_POETRY_PYTHON="true"
+
+	# Set the same env vars in the environment used by later buildpacks.
+	cat >>"${export_file}" <<-EOF
+		export PATH="${poetry_bin_dir}:\${PATH}"
+		export POETRY_VIRTUALENVS_CREATE="false"
+		export POETRY_VIRTUALENVS_USE_POETRY_PYTHON="true"
+	EOF
+}
+
+# Note: We cache site-packages since:
+# - It results in faster builds than only caching Poetry's download/wheel cache.
+# - It improves the UX of the build log, since Poetry will display which packages were
+#   added/removed since the last successful build.
+# - It's safe to do so, since `poetry sync` fully manages the environment (including
+#   e.g. uninstalling packages when they are removed from the lockfile).
+#
+# With site-packages cached there is no need to persist Poetry's download/wheel cache in the build
+# cache, so we let Poetry write it to the home directory where it will be discarded at the end of
+# the build. We don't use `--no-cache` since the cache still offers benefits (such as avoiding
+# repeat downloads of PEP-517/518 build requirements).
+function poetry::install_dependencies() {
+	local poetry_install_command=(
+		poetry
+		sync
+	)
+
+	# On Heroku CI, all default Poetry dependency groups are installed (i.e. all groups minus those
+	# marked as `optional = true`). Otherwise, only the 'main' Poetry dependency group is installed.
+	if [[ ! -v INSTALL_TEST ]]; then
+		poetry_install_command+=(--only main)
+	fi
+
+	# We only display the most relevant command args here, to improve the signal to noise ratio.
+	output::step "Installing dependencies using '${poetry_install_command[*]}'"
+
+	local install_log
+	install_log=$(mktemp)
+
+	# `--compile`: Compiles Python bytecode, to improve app boot times (pip does this by default).
+	# `--no-ansi`: Whilst we'd prefer to enable colour if possible, Poetry also emits ANSI escape
+	#              codes for redrawing lines, which renders badly in persisted build logs.
+	# shellcheck disable=SC2310 # This function is invoked in an 'if' condition so set -e will be disabled.
+	if ! {
+		"${poetry_install_command[@]}" \
+			--compile \
+			--no-ansi \
+			--no-interaction \
+			|& tee "${install_log}" \
+			|& sed --unbuffered --expression '/Skipping virtualenv creation/d' \
+			|& output::indent
+	}; then
+		# TODO: Overhaul warnings and combine them with error handling.
+		show-warnings "${install_log}"
+
+		output::error <<-EOF
+			Error: Unable to install dependencies using Poetry.
+
+			See the log output above for more information.
+		EOF
+		build_data::set_string "failure_reason" "install-dependencies::poetry"
+		exit 1
+	fi
+}
diff --git a/lib/python.sh b/lib/python.sh
new file mode 100644
index 000000000..0fa91862d
--- /dev/null
+++ b/lib/python.sh
@@ -0,0 +1,129 @@
+#!/usr/bin/env bash
+
+# This is technically redundant, since all consumers of this lib will have enabled these,
+# however, it helps Shellcheck realise the options under which these functions will run.
+set -euo pipefail
+
+S3_BASE_URL="https://heroku-buildpack-python.s3.dualstack.us-east-1.amazonaws.com"
+
+function python::install() {
+	local build_dir="${1}"
+	local stack="${2}"
+	local python_full_version="${3}"
+	local python_major_version="${4}"
+	local python_version_origin="${5}"
+
+	local install_python_start_time
+	install_python_start_time=$(build_data::current_unix_realtime)
+	local install_dir="${build_dir}/.heroku/python"
+
+	if [[ -f "${install_dir}/bin/python" ]]; then
+		output::step "Using cached install of Python ${python_full_version}"
+	else
+		output::step "Installing Python ${python_full_version}"
+
+		mkdir -p "${install_dir}"
+
+		# Calculating the Ubuntu version from the stack name saves having to shell out to `lsb_release`.
+		local ubuntu_version="${stack/heroku-/}.04"
+		local arch
+		arch=$(dpkg --print-architecture)
+		# e.g.: https://heroku-buildpack-python.s3.dualstack.us-east-1.amazonaws.com/python-3.14.0-ubuntu-24.04-amd64.tar.zst
+		local python_url="${S3_BASE_URL}/python-${python_full_version}-ubuntu-${ubuntu_version}-${arch}.tar.zst"
+
+		local error_log
+		error_log=$(mktemp)
+
+		# shellcheck disable=SC2310 # This function is invoked in an 'if' condition so set -e will be disabled.
+		if ! {
+			{
+				# We set max-time for improved UX/metrics for hanging downloads compared to relying on the build
+				# system timeout. We don't use `--speed-limit` since it gives worse error messages when used with
+				# retries and piping to tar. The Python archives are ~10 MB so only take ~1s to download on Heroku,
+				# so we set low timeouts to reduce delays before retries. However, we allow customising the timeouts
+				# to support non-Heroku environments that may be far from `us-east-1` or have a slower connection.
+				# We use `--no-progress-meter` rather than `--silent` so that retry status messages are printed.
+				curl \
+					--connect-timeout "${CURL_CONNECT_TIMEOUT:-3}" \
+					--fail \
+					--max-time "${CURL_TIMEOUT:-60}" \
+					--no-progress-meter \
+					--retry-max-time "${CURL_TIMEOUT:-60}" \
+					--retry 5 \
+					--retry-connrefused \
+					"${python_url}" \
+					| tar \
+						--directory "${install_dir}" \
+						--extract \
+						--zstd
+			} \
+				|& tee "${error_log}" \
+				|& output::indent
+		}; then
+			local latest_known_patch_version
+			latest_known_patch_version="$(python_version::resolve_python_version "${python_major_version}" "${python_version_origin}")"
+			# Ideally we would inspect the HTTP status code directly instead of grepping, however:
+			# 1. We want to pipe to tar (since it's faster than performing the download and
+			#    decompression/extraction as separate steps), so can't write to stdout.
+			# 2. We want to display the original stderr to the user, so can't write to stderr.
+			# 3. Curl's `--write-out` feature only supports outputting to a file (as opposed to
+			#    stdout/stderr) as of curl v8.3.0, which is newer than the curl on Heroku-22.
+			# This has an integration test run against all stacks, which will mean we will know
+			# if future versions of curl change the error message string.
+			#
+			# We have to check for HTTP 403s too, since S3 will return a 403 instead of a 404 for
+			# missing files, if the S3 bucket does not have public list permissions enabled.
+			if [[ "${python_full_version}" != "${latest_known_patch_version}" ]] && grep --quiet "The requested URL returned error: 40[34]" "${error_log}"; then
+				output::error <<-EOF
+					Error: The requested Python version isn't available.
+
+					Your app's ${python_version_origin} file specifies a Python version
+					of ${python_full_version}, however, we couldn't find that version on S3.
+
+					Check that this Python version has been released upstream,
+					and that the Python buildpack has added support for it:
+					https://www.python.org/downloads/
+					https://github.com/heroku/heroku-buildpack-python/blob/main/CHANGELOG.md
+
+					If it has, make sure that you are using the latest version
+					of this buildpack, and haven't pinned to an older release:
+					https://devcenter.heroku.com/articles/managing-buildpacks#view-your-buildpacks
+					https://devcenter.heroku.com/articles/managing-buildpacks#classic-buildpacks-references
+
+					We also strongly recommend that you don't pin your app to an
+					exact Python version such as ${python_full_version}, and instead only specify
+					the major Python version of ${python_major_version} in your ${python_version_origin} file.
+					This will allow your app to receive the latest available Python
+					patch version automatically, and prevent this type of error.
+				EOF
+				build_data::set_string "failure_reason" "python-version::unknown-patch"
+				build_data::set_string "failure_detail" "${python_full_version}"
+			else
+				output::error <<-EOF
+					Error: Unable to download/install Python.
+
+					An error occurred while downloading/installing the Python
+					runtime archive from:
+					${python_url}
+
+					In some cases, this happens due to a temporary issue with
+					the network connection or server.
+
+					First, make sure that you are using the latest version
+					of this buildpack, and haven't pinned to an older release:
+					https://devcenter.heroku.com/articles/managing-buildpacks#view-your-buildpacks
+					https://devcenter.heroku.com/articles/managing-buildpacks#classic-buildpacks-references
+
+					Then try building again to see if the error resolves itself.
+				EOF
+				build_data::set_string "failure_reason" "install-python"
+				# e.g.: 'curl: (6) Could not resolve host: heroku-buildpack-python.s3.dualstack.us-east-1.amazonaws.com'
+				build_data::set_string "failure_detail" "$(head --lines=1 "${error_log}" || true)"
+			fi
+
+			exit 1
+		fi
+	fi
+
+	build_data::set_duration "python_install_duration" "${install_python_start_time}"
+}
diff --git a/lib/python_version.sh b/lib/python_version.sh
new file mode 100644
index 000000000..0b814cd61
--- /dev/null
+++ b/lib/python_version.sh
@@ -0,0 +1,746 @@
+#!/usr/bin/env bash
+
+# This is technically redundant, since all consumers of this lib will have enabled these,
+# however, it helps Shellcheck realise the options under which these functions will run.
+set -euo pipefail
+
+LATEST_PYTHON_3_10="3.10.20"
+LATEST_PYTHON_3_11="3.11.15"
+LATEST_PYTHON_3_12="3.12.13"
+LATEST_PYTHON_3_13="3.13.14"
+LATEST_PYTHON_3_14="3.14.6"
+
+OLDEST_SUPPORTED_PYTHON_3_MINOR_VERSION=10
+NEWEST_SUPPORTED_PYTHON_3_MINOR_VERSION=14
+
+DEFAULT_PYTHON_FULL_VERSION="${LATEST_PYTHON_3_14}"
+DEFAULT_PYTHON_MAJOR_VERSION="${DEFAULT_PYTHON_FULL_VERSION%.*}"
+
+# Integer with no redundant leading zeros.
+INT_REGEX="(0|[1-9][0-9]*)"
+# Versions of form N.N or N.N.N.
+PYTHON_VERSION_REGEX="${INT_REGEX}\.${INT_REGEX}(\.${INT_REGEX})?"
+# Versions of form N.N.N only.
+PYTHON_FULL_VERSION_REGEX="${INT_REGEX}\.${INT_REGEX}\.${INT_REGEX}"
+
+# Misspellings of the `.python-version` file seen in the wild.
+MISSPELLED_PYTHON_VERSION_FILE_NAMES=(
+	" .python-version"
+	". python-version"
+	".python_version.txt"
+	".python_version"
+	".python-version "
+	",python-version"
+	".python-version."
+	".python-version.py"
+	".python-version.rtf"
+	".python-version.txt"
+	".python-version.TXT"
+	".Python-version"
+	".python.version"
+	".pythonversion"
+	"'.python-version'"
+	"python_version.txt"
+	"python_version"
+	"python-version."
+	"python-version.txt"
+	"python-version"
+)
+
+# Determine what Python version has been requested for the project.
+#
+# Returns a version request of form N.N or N.N.N, with basic validation checks that the version
+# matches those forms. EOL version checks will be performed later, when this version request is
+# resolved to an exact Python version.
+#
+# If an app specifies the Python version via multiple means, then the order of precedence is:
+# 1. `runtime.txt` file (deprecated)
+# 2. `.python-version` file (recommended)
+# 3. The `python_full_version` field in the `Pipfile.lock` file
+# 4. The `python_version` field in the `Pipfile.lock` file
+#
+# If a version wasn't specified by the app, then new apps/those with an empty cache will use
+# a buildpack default version for the first build, and then subsequent cached builds will use
+# the same Python major version in perpetuity (aka sticky versions). Sticky versioning leads to
+# confusing UX so is something we want to deprecate/sunset in the future (and have already done
+# so in the Python CNB).
+function python_version::read_requested_python_version() {
+	local build_dir="${1}"
+	local package_manager="${2}"
+	local cached_python_full_version="${3}"
+	# We use the Bash 4.3+ `nameref` feature to pass back multiple values from this function
+	# without having to hardcode globals. See: https://stackoverflow.com/a/38997681
+	declare -n version="${4}"
+	declare -n origin="${5}"
+
+	local runtime_txt_path="${build_dir}/runtime.txt"
+	if [[ -f "${runtime_txt_path}" ]]; then
+		version="$(python_version::parse_runtime_txt "${runtime_txt_path}")"
+		origin="runtime.txt"
+		return 0
+	fi
+
+	local misspelled_python_version_file_name
+	for misspelled_python_version_file_name in "${MISSPELLED_PYTHON_VERSION_FILE_NAMES[@]}"; do
+		if [[ -f "${build_dir}/${misspelled_python_version_file_name}" ]]; then
+			# We use quotes around the current filename since one of the misspellings seen in the
+			# wild is where the filename contains trailing whitespace.
+			output::error <<-EOF
+				Error: Your .python-version file is spelled incorrectly.
+
+				Your app's .python-version file currently has the filename:
+				'${misspelled_python_version_file_name}'
+
+				However, the correct spelling is (without quotes):
+				'.python-version'
+
+				You must rename your file to the correct name.
+			EOF
+			build_data::set_string "failure_reason" "python-version-file::misspelled"
+			build_data::set_string "failure_detail" "${misspelled_python_version_file_name}"
+			exit 1
+		fi
+	done
+
+	local python_version_file_path="${build_dir}/.python-version"
+	if [[ -f "${python_version_file_path}" ]]; then
+		version="$(python_version::parse_python_version_file "${python_version_file_path}")"
+		origin=".python-version"
+		return 0
+	fi
+
+	# Record the names of files similar to `.python-version` in the root of the app, so we can track
+	# additional misspellings that might need to be added to `MISSPELLED_PYTHON_VERSION_FILE_NAMES`.
+	local python_version_files
+	python_version_files="$(
+		find . -maxdepth 1 -type f -iregex '\./.*python.?version.*' -printf '%P\n' | sort | tr '\n' ',' || true
+	)"
+	if [[ -n "${python_version_files}" ]]; then
+		build_data::set_string "python_version_files" "${python_version_files}"
+	fi
+
+	if [[ "${package_manager}" == "pipenv" ]]; then
+		version="$(python_version::read_pipenv_python_version "${build_dir}")"
+		# The Python version fields in a Pipfile.lock are optional.
+		if [[ -n "${version}" ]]; then
+			origin="Pipfile.lock"
+			return 0
+		fi
+	fi
+
+	# Protect against unsupported (e.g. PyPy) or invalid versions being found in the cache metadata.
+	if [[ "${cached_python_full_version}" =~ ^${PYTHON_FULL_VERSION_REGEX}$ ]]; then
+		local cached_python_major_version="${cached_python_full_version%.*}"
+		version="${cached_python_major_version}"
+		origin="cached"
+	else
+		version="${DEFAULT_PYTHON_MAJOR_VERSION}"
+		# shellcheck disable=SC2034 # This isn't unused, Shellcheck doesn't follow namerefs.
+		origin="default"
+	fi
+}
+
+# Parse the contents of a runtime.txt file and return the Python version substring (e.g. `3.12` or `3.12.0`).
+function python_version::parse_runtime_txt() {
+	local runtime_txt_path="${1}"
+	local trimmed_contents
+	# The file contents with commented lines and leading/trailing whitespace removed.
+	trimmed_contents="$(python_version::read_trimmed_version_lines "${runtime_txt_path}")"
+
+	# The version must be of form `python-N.N` or `python-N.N.N`.
+	if [[ "${trimmed_contents}" =~ ^python-(${PYTHON_VERSION_REGEX})$ ]]; then
+		local version="${BASH_REMATCH[1]}"
+		echo "${version}"
+	else
+		local instructions
+		instructions="$(python_version::python_version_file_instructions "runtime.txt" "${DEFAULT_PYTHON_MAJOR_VERSION}")"
+		# We intentionally don't display the current contents of the file here, to prevent users
+		# from copying that into the .python-version file instead of our example valid version.
+		output::error <<-EOF
+			Error: Invalid Python version in runtime.txt.
+
+			The Python version specified in your runtime.txt file isn't
+			in the correct format.
+
+			However, the runtime.txt file is deprecated since it has been
+			replaced by the more widely supported .python-version file:
+			https://devcenter.heroku.com/changelog-items/3141
+
+			As such, we recommend that you switch to using .python-version
+			instead of fixing your runtime.txt file.
+
+			${instructions}
+		EOF
+		build_data::set_string "failure_reason" "runtime-txt::invalid-version"
+		build_data::set_string "failure_detail" "${trimmed_contents:0:100}"
+		exit 1
+	fi
+}
+
+# Parse the contents of a .python-version file and return the Python version substring (e.g. `3.12` or `3.12.0`).
+function python_version::parse_python_version_file() {
+	local python_version_file_path="${1}"
+	local versions=()
+	local version
+
+	# shellcheck disable=SC2312 # Shellcheck doesn't take the `wait $!` into account.
+	mapfile -t versions < <(python_version::read_trimmed_version_lines "${python_version_file_path}")
+	# Ensure that if `python_version::read_trimmed_version_lines` fails inside the process
+	# substitution that the non-zero exit status is propagated.
+	wait $!
+
+	# We validate all of the version lines up front, since in the case where there are multiple invalid
+	# versions, we want to show an "invalid version" error rather than the "multiple versions" error.
+	for version in "${versions[@]}"; do
+		if [[ "${version}" =~ ^${PYTHON_VERSION_REGEX}$ ]]; then
+			continue
+		fi
+
+		# If we didn't find a valid Python version string, we check the text encoding so that we
+		# can display a more helpful error message if it turns out that the version was valid but
+		# that the file was just saved in the wrong encoding (such as UTF-8 with BOM or UTF-16).
+		#
+		# Example values `file` can return:
+		# `ASCII text`
+		# `ASCII text, with CRLF line terminators`
+		# `ASCII text, with no line terminators`
+		# `Unicode text, UTF-8 text`
+		# `Unicode text, UTF-8 (with BOM) text`
+		# `Unicode text, UTF-16, little-endian text, with CRLF line terminators`
+		# `data` (such as when the file contains a NUL or other control code characters)
+		# `very short file (no magic)` (such as when the file contains a single ESC character)
+		#
+		# Note: File can also return `empty` but in that case we wouldn't be iterating over found lines.
+		local file_encoding
+		# We exclude some file type tests to avoid false positives, since we only need the encoding.
+		file_encoding="$(file --brief --dereference --exclude json --exclude soft "${python_version_file_path}")"
+
+		case "${file_encoding}" in
+			# Cases where the text encoding isn't the issue, and so the version itself must be invalid.
+			*"ASCII text"* | *"UTF-8 text"* | *"very short file"* | "data")
+				# Replace everything but printable ASCII, spaces and tabs with the Unicode replacement
+				# character, so any invisible unwanted characters (such as ASCII control codes or the
+				# Unicode zero width space character) are visible in the error message.
+				local escaped_version
+				escaped_version="$(
+					LC_ALL=C
+					echo "${version//[^[:print:][:blank:]]/�}"
+				)"
+				output::error <<-EOF
+					Error: Invalid Python version in .python-version.
+
+					The Python version specified in your .python-version file
+					isn't in the correct format.
+
+					The following version was found:
+					${escaped_version}
+
+					However, the Python version must be specified as either:
+					1. The major version only, for example: ${DEFAULT_PYTHON_MAJOR_VERSION} (recommended)
+					2. An exact patch version, for example: ${DEFAULT_PYTHON_MAJOR_VERSION}.999
+
+					Don't include quotes, a 'python-' prefix or wildcards. Any
+					code comments must be on a separate line prefixed with '#'.
+
+					For example, to request the latest version of Python ${DEFAULT_PYTHON_MAJOR_VERSION},
+					update your .python-version file so it contains exactly:
+					${DEFAULT_PYTHON_MAJOR_VERSION}
+
+					We strongly recommend that you don't specify the Python patch
+					version number, since it will pin your app to an exact Python
+					version and so stop your app from receiving security updates
+					each time it builds.
+				EOF
+				build_data::set_string "failure_reason" "python-version-file::invalid-version"
+				build_data::set_string "failure_detail" "${version:0:100}"
+				exit 1
+				;;
+			# Unsupported text encodings such as UTF-8 with BOM or UTF-16.
+			*)
+				output::error <<-EOF
+					Error: Unable to read .python-version.
+
+					Your .python-version file couldn't be read because it's using
+					an unsupported text encoding:
+					${file_encoding}
+
+					Configure your editor to save files as UTF-8, without a BOM,
+					then delete and recreate the file using the correct encoding.
+
+					If that doesn't work, make sure you don't have a .gitattributes
+					file that's overriding the text encoding.
+
+					Note: On Windows, if you pipe or redirect output to a file
+					it can result in the file being encoded in UTF-16 LE when
+					using certain terminals and Windows settings. We recommend
+					you create the file using a text editor instead.
+				EOF
+				build_data::set_string "failure_reason" "python-version-file::invalid-encoding"
+				build_data::set_string "failure_detail" "${file_encoding}"
+				exit 1
+				;;
+		esac
+	done
+
+	case "${#versions[@]}" in
+		1)
+			echo "${versions[0]}"
+			return 0
+			;;
+		0)
+			output::error <<-EOF
+				Error: No Python version found in .python-version.
+
+				No Python version was found in your .python-version file.
+
+				Update the file so that it contains your app's major Python
+				version number. Don't include quotes or a 'python-' prefix.
+
+				For example, to request the latest version of Python ${DEFAULT_PYTHON_MAJOR_VERSION},
+				update your .python-version file so it contains exactly:
+				${DEFAULT_PYTHON_MAJOR_VERSION}
+
+				If the file already contains a version, check the line doesn't
+				begin with a '#', otherwise it will be treated as a comment.
+			EOF
+			build_data::set_string "failure_reason" "python-version-file::no-version"
+			exit 1
+			;;
+		*)
+			output::error <<-EOF
+				Error: Multiple Python versions found in .python-version.
+
+				Multiple versions were found in your .python-version file:
+
+				$(
+					IFS=$'\n'
+					echo "${versions[*]}"
+				)
+
+				Update the file so it contains only one Python version.
+
+				For example, to request the latest version of Python ${DEFAULT_PYTHON_MAJOR_VERSION},
+				update your .python-version file so it contains exactly:
+				${DEFAULT_PYTHON_MAJOR_VERSION}
+			EOF
+			build_data::set_string "failure_reason" "python-version-file::multiple-versions"
+			build_data::set_string "failure_detail" "$(
+				IFS=,
+				echo "${versions[*]}"
+			)"
+			exit 1
+			;;
+	esac
+}
+
+# Outputs all populated (non-empty and not commented with '#') lines from the passed file,
+# with leading/trailing whitespace (including Unicode whitespace) trimmed from each line.
+# We replace any NUL characters with a placeholder since Bash variables can't store them.
+function python_version::read_trimmed_version_lines() {
+	local file="${1}"
+	LC_ALL=C.UTF-8 sed \
+		--regexp-extended \
+		--expression 's/^[[:space:]]+//' \
+		--expression 's/[[:space:]]+$//' \
+		--expression 's/\x0/␀/g' \
+		--expression '/^(#|$)/d' \
+		"${file}"
+}
+
+# Read the Python version from a Pipfile.lock, which can exist in one of two optional fields,
+# `python_full_version` (as N.N.N) and `python_version` (as N.N). If both fields are
+# defined, we will use the value set in `python_full_version`. See:
+# https://pipenv.pypa.io/en/stable/specifiers.html#specifying-versions-of-python
+function python_version::read_pipenv_python_version() {
+	local build_dir="${1}"
+	local pipfile_lock_path="${build_dir}/Pipfile.lock"
+	local version
+
+	if ! version=$(jq --raw-output '._meta.requires.python_full_version // ._meta.requires.python_version' "${pipfile_lock_path}" 2>&1); then
+		local jq_error_message="${version}"
+		output::error <<-EOF
+			Error: Can't parse Pipfile.lock.
+
+			A Pipfile.lock file was found, however, it couldn't be parsed:
+			${jq_error_message}
+
+			This is likely due to it not being valid JSON.
+
+			Run 'pipenv lock' to regenerate/fix the lockfile.
+		EOF
+		build_data::set_string "failure_reason" "pipfile-lock::invalid-json"
+		build_data::set_string "failure_detail" "${jq_error_message:0:100}"
+		exit 1
+	fi
+
+	# Neither of the optional fields were found.
+	if [[ "${version}" == "null" ]]; then
+		return 0
+	fi
+
+	# We don't use separate version validation rules for both fields (e.g. ensuring a patch version
+	# only exists for `python_full_version`) since Pipenv doesn't distinguish between them either:
+	# https://github.com/pypa/pipenv/blob/v2024.1.0/pipenv/project.py#L392-L398
+	if [[ "${version}" =~ ^${PYTHON_VERSION_REGEX}$ ]]; then
+		echo "${version}"
+	else
+		output::error <<-EOF
+			Error: Invalid Python version in Pipfile.lock.
+
+			The Python version specified in your Pipfile.lock file by the
+			'python_version' or 'python_full_version' fields isn't valid.
+
+			The following version was found:
+			${version}
+
+			However, the Python version must be specified as either:
+			1. The major version only, for example: ${DEFAULT_PYTHON_MAJOR_VERSION} (recommended)
+			2. An exact patch version, for example: ${DEFAULT_PYTHON_MAJOR_VERSION}.999
+
+			Wildcards aren't supported.
+
+			Please update your Pipfile to use a valid Python version and
+			then run 'pipenv lock' to regenerate Pipfile.lock.
+
+			We strongly recommend that you don't specify the Python patch
+			version number, since it will pin your app to an exact Python
+			version and so stop your app from receiving security updates
+			each time it builds.
+
+			For more information, see:
+			https://pipenv.pypa.io/en/stable/specifiers.html#specifying-versions-of-python
+		EOF
+		build_data::set_string "failure_reason" "pipfile-lock::invalid-version"
+		build_data::set_string "failure_detail" "${version:0:50}"
+		exit 1
+	fi
+}
+
+# Resolve a requested Python version (which can be of form N.N or N.N.N) to a specific
+# Python version of form N.N.N. Rejects Python major versions that aren't supported.
+function python_version::resolve_python_version() {
+	local requested_python_version="${1}"
+	local python_version_origin="${2}"
+
+	if [[ ! "${requested_python_version}" =~ ^${PYTHON_VERSION_REGEX}$ ]]; then
+		# The Python version was previously validated, so this should never occur.
+		utils::abort_internal_error "Invalid Python version: ${requested_python_version}"
+	fi
+
+	local major="${BASH_REMATCH[1]}"
+	local minor="${BASH_REMATCH[2]}"
+
+	if ((major < 3 || (major == 3 && minor < OLDEST_SUPPORTED_PYTHON_3_MINOR_VERSION))); then
+		if [[ "${python_version_origin}" == "cached" ]]; then
+			local instructions
+			instructions="$(python_version::python_version_file_instructions "${python_version_origin}" "3.${OLDEST_SUPPORTED_PYTHON_3_MINOR_VERSION}")"
+			output::error <<-EOF
+				Error: The cached Python version has reached end-of-life.
+
+				Your app doesn't specify a Python version, and so normally
+				would use the version cached from the last build (${requested_python_version}).
+
+				However, Python ${major}.${minor} has reached its upstream end-of-life,
+				and is therefore no longer receiving security updates:
+				https://devguide.python.org/versions/#supported-versions
+
+				As such, it's no longer supported by this buildpack:
+				https://devcenter.heroku.com/articles/python-support#supported-python-versions
+
+				Please upgrade to at least Python 3.${OLDEST_SUPPORTED_PYTHON_3_MINOR_VERSION} by configuring an
+				explicit Python version for your app.
+
+				${instructions}
+			EOF
+		else
+			output::error <<-EOF
+				Error: The requested Python version has reached end-of-life.
+
+				Python ${major}.${minor} has reached its upstream end-of-life, and is
+				therefore no longer receiving security updates:
+				https://devguide.python.org/versions/#supported-versions
+
+				As such, it's no longer supported by this buildpack:
+				https://devcenter.heroku.com/articles/python-support#supported-python-versions
+
+				Please upgrade to at least Python 3.${OLDEST_SUPPORTED_PYTHON_3_MINOR_VERSION} by changing the
+				version in your ${python_version_origin} file.
+
+				If possible, we recommend upgrading all the way to Python ${DEFAULT_PYTHON_MAJOR_VERSION},
+				since it contains many performance and usability improvements.
+			EOF
+		fi
+		build_data::set_string "failure_reason" "python-version::eol"
+		build_data::set_string "failure_detail" "${major}.${minor}"
+		exit 1
+	fi
+
+	if (((major == 3 && minor > NEWEST_SUPPORTED_PYTHON_3_MINOR_VERSION) || major >= 4)); then
+		if [[ "${python_version_origin}" == "cached" ]]; then
+			output::error <<-EOF
+				Error: The cached Python version isn't recognised.
+
+				Your app doesn't specify a Python version, and so normally
+				would use the version cached from the last build (${requested_python_version}).
+
+				However, Python ${major}.${minor} isn't recognised by this version
+				of the buildpack.
+
+				This can occur if you have downgraded the version of the
+				buildpack to an older version.
+
+				Please switch back to a newer version of this buildpack:
+				https://devcenter.heroku.com/articles/managing-buildpacks#view-your-buildpacks
+				https://devcenter.heroku.com/articles/managing-buildpacks#classic-buildpacks-references
+
+				Alternatively, request an older Python version by creating
+				a .python-version file in the root directory of your app,
+				that contains a Python version like:
+				3.${NEWEST_SUPPORTED_PYTHON_3_MINOR_VERSION}
+			EOF
+		else
+			output::error <<-EOF
+				Error: The requested Python version isn't recognised.
+
+				The requested Python version ${major}.${minor} isn't recognised.
+
+				Check that this Python version has been officially released,
+				and that the Python buildpack has added support for it:
+				https://devguide.python.org/versions/#supported-versions
+				https://devcenter.heroku.com/articles/python-support#supported-python-versions
+
+				If it has, make sure that you are using the latest version
+				of this buildpack, and haven't pinned to an older release:
+				https://devcenter.heroku.com/articles/managing-buildpacks#view-your-buildpacks
+				https://devcenter.heroku.com/articles/managing-buildpacks#classic-buildpacks-references
+
+				Otherwise, switch to a supported version (such as Python 3.${NEWEST_SUPPORTED_PYTHON_3_MINOR_VERSION})
+				by changing the version in your ${python_version_origin} file.
+			EOF
+		fi
+		build_data::set_string "failure_reason" "python-version::unknown-major"
+		build_data::set_string "failure_detail" "${major}.${minor}"
+		exit 1
+	fi
+
+	# If an exact Python version was requested, there's nothing to resolve.
+	# Otherwise map major version specifiers to the latest patch release.
+	case "${requested_python_version}" in
+		*.*.*) echo "${requested_python_version}" ;;
+		3.10) echo "${LATEST_PYTHON_3_10}" ;;
+		3.11) echo "${LATEST_PYTHON_3_11}" ;;
+		3.12) echo "${LATEST_PYTHON_3_12}" ;;
+		3.13) echo "${LATEST_PYTHON_3_13}" ;;
+		3.14) echo "${LATEST_PYTHON_3_14}" ;;
+		*) utils::abort_internal_error "Unhandled Python major version: ${requested_python_version}" ;;
+	esac
+}
+
+function python_version::warn_or_error_if_python_version_file_missing() {
+	local python_version_origin="${1}"
+	local python_major_version="${2}"
+	local package_manager="${3}"
+
+	if [[ "${python_version_origin}" == ".python-version" ]]; then
+		return 0
+	fi
+
+	local instructions
+	instructions="$(python_version::python_version_file_instructions "${python_version_origin}" "${python_major_version}")"
+
+	case "${python_version_origin}" in
+		default | cached)
+			if [[ "${package_manager}" == "uv" ]]; then
+				output::error <<-EOF
+					Error: No Python version was specified.
+
+					When using the package manager uv on Heroku, you must specify
+					your app's Python version with a .python-version file.
+
+					To add a .python-version file:
+
+					1. Make sure you are in the root directory of your app
+					   and not a subdirectory.
+					2. Run 'uv python pin ${python_major_version}'
+					   (adjust to match your app's major Python version).
+					3. Commit the changes to your Git repository using
+					   'git add --all' and then 'git commit'.
+
+					Note: We strongly recommend that you don't specify the Python
+					patch version number in your .python-version file, since it will
+					pin your app to an exact Python version and so stop your app from
+					receiving security updates each time it builds.
+				EOF
+				build_data::set_string "failure_reason" "python-version-file::not-found"
+				exit 1
+			fi
+
+			output::warning <<-EOF
+				Warning: No Python version was specified.
+
+				Your app doesn't specify a Python version and so the buildpack
+				picked a default version for you.
+
+				Relying on this default version isn't recommended, since it
+				can change over time and may not be consistent with your local
+				development environment, CI or other instances of your app.
+
+				Please configure an explicit Python version for your app.
+
+				${instructions}
+
+				If your app already has a .python-version file, check that it:
+
+				1. Is in the top level directory (not a subdirectory).
+				2. Is named exactly '.python-version' in all lowercase.
+				3. Isn't listed in '.gitignore' or '.slugignore'.
+				4. Has been added to the Git repository using 'git add --all'
+				   and then committed using 'git commit'.
+
+				In the future we will require the use of a .python-version
+				file and this warning will be made an error.
+			EOF
+			;;
+		runtime.txt)
+			if [[ "${package_manager}" == "uv" ]]; then
+				output::error <<-EOF
+					Error: The runtime.txt file isn't supported when using uv.
+
+					When using the package manager uv on Heroku, you must specify
+					your app's Python version with a .python-version file and not
+					a runtime.txt file.
+
+					To switch to a .python-version file:
+
+					1. Make sure you are in the root directory of your app
+					   and not a subdirectory.
+					2. Delete your runtime.txt file.
+					3. Run 'uv python pin ${python_major_version}'
+					   (adjust to match your app's major Python version).
+					4. Commit the changes to your Git repository using
+					   'git add --all' and then 'git commit'.
+
+					Note: We strongly recommend that you don't specify the Python
+					patch version number in your .python-version file, since it will
+					pin your app to an exact Python version and so stop your app from
+					receiving security updates each time it builds.
+				EOF
+				build_data::set_string "failure_reason" "runtime-txt::not-supported"
+				exit 1
+			fi
+
+			output::warning <<-EOF
+				Warning: The runtime.txt file is deprecated.
+
+				The runtime.txt file is deprecated since it has been replaced
+				by the more widely supported .python-version file:
+				https://devcenter.heroku.com/changelog-items/3141
+
+				Please switch to using a .python-version file instead.
+
+				${instructions}
+
+				In the future support for runtime.txt will be removed and
+				this warning will be made an error.
+			EOF
+			;;
+		Pipfile.lock)
+			# Decide if we want to warn for this case.
+			;;
+		*) utils::abort_internal_error "Unhandled Python version origin: ${python_version_origin}" ;;
+	esac
+}
+
+function python_version::python_version_file_instructions() {
+	local python_version_origin="${1}"
+	local python_major_version="${2}"
+
+	if [[ "${python_version_origin}" == "runtime.txt" ]]; then
+		cat <<-EOF
+			Delete your runtime.txt file and create a new file in the
+			root directory of your app named:
+		EOF
+	else
+		cat <<-EOF
+			Create a new file in the root directory of your app named:
+		EOF
+	fi
+
+	cat <<-EOF
+		.python-version
+
+		Make sure to include the '.' character at the start of the
+		filename. Don't add a file extension such as '.txt'.
+
+		In the new file, specify your app's major Python version number
+		only. Don't include quotes or a 'python-' prefix.
+
+		For example, to request the latest version of Python ${python_major_version},
+		update your .python-version file so it contains exactly:
+		${python_major_version}
+
+		We strongly recommend that you don't specify the Python patch
+		version number, since it will pin your app to an exact Python
+		version and so stop your app from receiving security updates
+		each time it builds.
+	EOF
+}
+
+function python_version::warn_if_deprecated_major_version() {
+	local requested_major_version="${1}"
+	local version_origin="${2}"
+
+	if [[ "${requested_major_version}" == "3.10" ]]; then
+		output::warning <<-EOF
+			Warning: Support for Python 3.10 is deprecated!
+
+			Python 3.10 will reach its upstream end-of-life in October 2026,
+			at which point it will no longer receive security updates:
+			https://devguide.python.org/versions/#supported-versions
+
+			As such, support for Python 3.10 will be removed from this
+			buildpack on 6th January 2027.
+
+			Upgrade to a newer Python version as soon as possible, by
+			changing the version in your ${version_origin} file.
+
+			For more information, see:
+			https://devcenter.heroku.com/articles/python-support#supported-python-versions
+		EOF
+	fi
+}
+
+function python_version::warn_if_patch_update_available() {
+	local python_full_version="${1}"
+	local python_major_version="${2}"
+	local python_version_origin="${3}"
+
+	local latest_known_patch_version
+	latest_known_patch_version="$(python_version::resolve_python_version "${python_major_version}" "${python_version_origin}")"
+	# Extract the patch version component of the version strings (ie: the '2' in '3.13.2').
+	local requested_patch_number="${python_full_version##*.}"
+	local latest_patch_number="${latest_known_patch_version##*.}"
+
+	if ((requested_patch_number < latest_patch_number)); then
+		output::warning <<-EOF
+			Warning: A Python patch update is available!
+
+			Your app is using Python ${python_full_version}, however, there is a newer
+			patch release of Python ${python_major_version} available: ${latest_known_patch_version}
+
+			It is important to always use the latest patch version of
+			Python to keep your app secure.
+
+			Update your ${python_version_origin} file to use the new version.
+
+			We strongly recommend that you don't pin your app to an
+			exact Python version such as ${python_full_version}, and instead only specify
+			the major Python version of ${python_major_version} in your ${python_version_origin} file.
+			This will allow your app to receive the latest available Python
+			patch version automatically and prevent this warning.
+		EOF
+		build_data::set_raw "python_version_outdated" "true"
+	else
+		build_data::set_raw "python_version_outdated" "false"
+	fi
+}
diff --git a/lib/utils.sh b/lib/utils.sh
new file mode 100644
index 000000000..4a05e2897
--- /dev/null
+++ b/lib/utils.sh
@@ -0,0 +1,95 @@
+#!/usr/bin/env bash
+
+# This is technically redundant, since all consumers of this lib will have enabled these,
+# however, it helps Shellcheck realise the options under which these functions will run.
+set -euo pipefail
+
+# The requirement versions are effectively buildpack constants, however, we want
+# Dependabot to be able to update them, which requires that they be in requirements
+# files. The requirements files contain contents like `package==1.2.3` (and not just
+# the package version) so we have to extract the version substring from it.
+function utils::get_requirement_version() {
+	local package_name="${1}"
+	local requirement
+	requirement=$(cat "${BUILDPACK_DIR:?}/requirements/${package_name}.txt")
+	local requirement_version="${requirement#"${package_name}=="}"
+	echo "${requirement_version}"
+}
+
+# Python bundles pip within its standard library, which we can use to install our chosen
+# pip version from PyPI, saving us from having to download the usual pip bootstrap script.
+function utils::bundled_pip_module_path() {
+	local python_home="${1}"
+	local python_major_version="${2}"
+
+	local bundled_wheels_dir="${python_home}/lib/python${python_major_version}/ensurepip/_bundled"
+
+	# We have to use a glob since the bundled wheel filename contains the pip version, which differs
+	# between Python versions. We use compgen to avoid having to set nullglob, since there may be no
+	# matches in the case of a broken Python install. We also have to handle the case where there are
+	# multiple matching pip wheels, since in some versions of Python (e.g. 3.9.0) multiple versions of
+	# pip were accidentally bundled upstream (we use tail since we want the newest pip version).
+	if bundled_pip_wheel="$(compgen -G "${bundled_wheels_dir}/pip-*.whl" | tail --lines=1)"; then
+		# The pip module exists inside the pip wheel (which is a zip file), however, Python can load
+		# it directly by appending the module name to the zip filename, as though it were a path.
+		echo "${bundled_pip_wheel}/pip"
+	else
+		output::error <<-EOF
+			Internal Error: Unable to locate the Python stdlib's bundled pip.
+
+			Couldn't find the pip wheel file bundled inside the Python
+			stdlib's 'ensurepip' module:
+
+			$(find "${bundled_wheels_dir}/" 2>&1 || find "${python_home}/" -type d 2>&1 || true)
+		EOF
+		build_data::set_string "failure_reason" "internal-error::bundled-pip-not-found"
+		exit 1
+	fi
+}
+
+function utils::abort_internal_error() {
+	local message
+	message="${1} (line $(caller || true))"
+	output::error <<-EOF
+		Internal error: ${message}.
+	EOF
+	build_data::set_string "failure_reason" "internal-error::abort"
+	build_data::set_string "failure_detail" "${message}"
+	exit 1
+}
+
+function utils::err_trap() {
+	# We use `errtrace` which means the ERR trap can fire multiple times, such as when an error
+	# occurs in a buildpack function called from within a command substitution.
+	# shellcheck disable=SC2310 # This function is invoked in an 'if' condition so set -e will be disabled.
+	if build_data::has "failure_reason"; then
+		return
+	fi
+
+	local failing_command="${BASH_COMMAND}"
+	local stack_trace
+	stack_trace=$(
+		local frame=0
+		while read -r line_number function_name source_file < <(caller "${frame}" || true); do
+			echo "${function_name} @ ${source_file}:${line_number}"
+			((++frame))
+		done
+	)
+
+	output::error <<-EOF
+		Internal Error: An unhandled buildpack error occurred.
+
+		An unhandled error occurred while executing the command:
+		${failing_command}
+
+		If this issue persists, please open a support ticket or file
+		an issue on the buildpack's GitHub repository:
+		https://help.heroku.com/
+		https://github.com/heroku/heroku-buildpack-python/issues
+
+		Stack trace:
+		${stack_trace}
+	EOF
+	build_data::set_string "failure_reason" "internal-error::unhandled"
+	build_data::set_string "failure_detail" "${failing_command}"
+}
diff --git a/lib/uv.sh b/lib/uv.sh
new file mode 100644
index 000000000..cdbef4acb
--- /dev/null
+++ b/lib/uv.sh
@@ -0,0 +1,181 @@
+#!/usr/bin/env bash
+
+# This is technically redundant, since all consumers of this lib will have enabled these,
+# however, it helps Shellcheck realise the options under which these functions will run.
+set -euo pipefail
+
+UV_VERSION=$(utils::get_requirement_version 'uv')
+
+function uv::install_uv() {
+	local cache_dir="${1}"
+	local export_file="${2}"
+	local python_home="${3}"
+
+	# We store uv in the build cache, since we only need it during the build.
+	local uv_dir="${cache_dir}/.heroku/python-uv"
+
+	build_data::set_string "uv_version" "${UV_VERSION}"
+
+	# The earlier buildpack cache invalidation step will have already handled the case where
+	# the uv version has changed, so here we only need to check whether the uv binary exists.
+	if [[ -f "${uv_dir}/uv" ]]; then
+		output::step "Using cached uv ${UV_VERSION}"
+	else
+		output::step "Installing uv ${UV_VERSION}"
+		mkdir -p "${uv_dir}"
+
+		local gnu_arch
+		# e.g.: `x86_64` or `aarch64`.
+		gnu_arch=$(arch)
+		local uv_url="https://releases.astral.sh/github/uv/releases/download/${UV_VERSION}/uv-${gnu_arch}-unknown-linux-gnu.tar.gz"
+
+		local error_log
+		error_log=$(mktemp)
+
+		# shellcheck disable=SC2310 # This function is invoked in an 'if' condition so set -e will be disabled.
+		if ! {
+			{
+				# We set max-time for improved UX/metrics for hanging downloads compared to relying on the build
+				# system timeout. We don't use `--speed-limit` since it gives worse error messages when used with
+				# retries and piping to tar. The uv archives are ~20 MB so only take ~1s to download on Heroku,
+				# so we set low timeouts to reduce delays before retries. However, we allow customising the timeouts
+				# to support non-Heroku environments that may be far from `us-east-1` or have a slower connection.
+				# We use `--no-progress-meter` rather than `--silent` so that retry status messages are printed.
+				# We have to use `--strip-components` since the uv binary is nested under a subdirectory.
+				curl \
+					--connect-timeout "${CURL_CONNECT_TIMEOUT:-3}" \
+					--fail \
+					--location \
+					--max-time "${CURL_TIMEOUT:-60}" \
+					--no-progress-meter \
+					--retry-max-time "${CURL_TIMEOUT:-60}" \
+					--retry 5 \
+					--retry-connrefused \
+					"${uv_url}" \
+					| tar \
+						--directory "${uv_dir}" \
+						--extract \
+						--gzip \
+						--strip-components 1
+			} \
+				|& tee "${error_log}" \
+				|& output::indent
+		}; then
+			output::error <<-EOF
+				Error: Unable to install uv.
+
+				Failed to download/install uv from:
+				${uv_url}
+
+				In some cases, this happens due to a temporary issue with
+				the network connection or Astral's CDN, Cloudflare.
+
+				Try building again to see if the error resolves itself.
+
+				If that doesn't help, check the status of Cloudflare here:
+				https://www.cloudflarestatus.com
+			EOF
+			build_data::set_string "failure_reason" "install-package-manager::uv"
+			# e.g.: 'curl: (56) Recv failure: Connection reset by peer'
+			build_data::set_string "failure_detail" "$(head --lines=1 "${error_log}" || true)"
+			exit 1
+		fi
+	fi
+
+	export PATH="${uv_dir}:${PATH}"
+	# Make uv manage the system site-packages of our Python install instead of creating a venv.
+	export UV_PROJECT_ENVIRONMENT="${python_home}"
+	# Prevent uv from downloading/using its own Python installation.
+	export UV_NO_MANAGED_PYTHON="1"
+	export UV_PYTHON_DOWNLOADS="never"
+	# Force uv to use hardlinks rather than the new default of reflinks, since the latter are
+	# significantly slower on Kodon: https://github.com/astral-sh/uv/issues/18259
+	export UV_LINK_MODE="hardlink"
+
+	# Set the same env vars in the environment used by later buildpacks.
+	cat >>"${export_file}" <<-EOF
+		export PATH="${uv_dir}:\${PATH}"
+		export UV_PROJECT_ENVIRONMENT="${python_home}"
+		export UV_NO_MANAGED_PYTHON="1"
+		export UV_PYTHON_DOWNLOADS="never"
+		export UV_LINK_MODE="hardlink"
+	EOF
+
+	# As a performance optimisation, uv attempts to use hardlinks instead of copying files from its
+	# download cache into site-packages, and will emit a warning if it has to fall back to copying.
+	# By default uv stores its cache under `$HOME/.cache`, and for standard Heroku builds `$HOME` is
+	# `/app`, which is on a different filesystem mount to the build directory (which is under `/tmp`),
+	# meaning hardlinks can't be used. To avoid this we tell uv to store its cache in `/tmp`.
+	# However, we have to do so conditionally, since for Heroku CI both the home directory and
+	# the build directory are `/app`, where hardlinks already work and changing the cache to `/tmp`
+	# would instead break them.
+	#
+	# There's also a third case, a non-CI build where the app has the undocumented `build-in-app-dir`
+	# labs enabled, however, for that scenario the build directory is `/app` and the home directory
+	# is `/tmp`, so we can't use hardlinks unless we wrote the cache to the build directory and
+	# manually deleted it after. For now we ignore this case since not many apps use that labs,
+	# and uv will still work after falling back to copying files (with a warning).
+	#
+	# Longer term, ideally uv's `--no-cache` option would co-locate the temporary cache it writes
+	# alongside site-packages (see https://github.com/astral-sh/uv/issues/11385), and we could use
+	# that everywhere since we don't actually need to persist uv's cache (see below).
+	# shellcheck disable=SC2312 # Invoke this command separately to avoid masking its return value.
+	if [[ "$(realpath "${python_home}")" =~ ^/tmp/ ]]; then
+		export UV_CACHE_DIR='/tmp/uv-cache'
+		echo 'export UV_CACHE_DIR="/tmp/uv-cache"' >>"${export_file}"
+	fi
+}
+
+# Note: We cache site-packages since:
+# - It results in faster builds than only caching uv's download/wheel cache.
+# - It improves the UX of the build log, since uv will display which packages were
+#   added/removed since the last successful build.
+# - It's safe to do so, since `uv sync` fully manages the environment (including
+#   e.g. uninstalling packages when they are removed from the lockfile).
+#
+# With site-packages cached there is no need to persist uv's cache in the build cache, so we let
+# uv write it to the home directory (or `UV_CACHE_DIR`, see above) where it will be discarded at
+# the end of the build. We don't use `--no-cache` since all it does is make uv switch to a temporary
+# cache directory under `/tmp`, which would mean hardlinks can't be used for Heroku CI (see above).
+function uv::install_dependencies() {
+	local uv_install_command=(
+		uv
+		sync
+		--locked
+	)
+
+	# Unless we're building on Heroku CI, we omit the default dependency groups (such as `dev`):
+	# https://docs.astral.sh/uv/concepts/projects/dependencies/#dependency-groups
+	if [[ ! -v INSTALL_TEST ]]; then
+		uv_install_command+=(--no-default-groups)
+	fi
+
+	# We only display the most relevant command args here, to improve the signal to noise ratio.
+	output::step "Installing dependencies using '${uv_install_command[*]}'"
+
+	local install_log
+	install_log=$(mktemp)
+
+	# TODO: Expose app config vars to the install command as part of doing so for all package managers.
+	# `--compile-bytecode`: Improves app boot times (pip does this by default).
+	# shellcheck disable=SC2310 # This function is invoked in an 'if' condition so set -e will be disabled.
+	if ! {
+		"${uv_install_command[@]}" \
+			--color always \
+			--compile-bytecode \
+			--no-progress \
+			|& tee "${install_log}" \
+			|& output::indent
+	}; then
+		# TODO: Overhaul warnings and combine them with error handling (for all package managers).
+		show-warnings "${install_log}"
+
+		output::error <<-EOF
+			Error: Unable to install dependencies using uv.
+
+			See the log output above for more information.
+		EOF
+		build_data::set_string "failure_reason" "install-dependencies::uv"
+		exit 1
+	fi
+}
diff --git a/requirements/pip.txt b/requirements/pip.txt
index f293eef6f..657e2159e 100644
--- a/requirements/pip.txt
+++ b/requirements/pip.txt
@@ -1 +1 @@
-pip==24.0
+pip==26.1.2
diff --git a/requirements/pipenv.txt b/requirements/pipenv.txt
index 34b9e5c44..5392a7319 100644
--- a/requirements/pipenv.txt
+++ b/requirements/pipenv.txt
@@ -1 +1 @@
-pipenv==2024.0.1
+pipenv==2026.6.2
diff --git a/requirements/poetry.txt b/requirements/poetry.txt
new file mode 100644
index 000000000..c3973d4c7
--- /dev/null
+++ b/requirements/poetry.txt
@@ -0,0 +1 @@
+poetry==2.4.1
diff --git a/requirements/setuptools.txt b/requirements/setuptools.txt
deleted file mode 100644
index d125505ce..000000000
--- a/requirements/setuptools.txt
+++ /dev/null
@@ -1 +0,0 @@
-setuptools==70.3.0
diff --git a/requirements/uv.txt b/requirements/uv.txt
new file mode 100644
index 000000000..f329fecf5
--- /dev/null
+++ b/requirements/uv.txt
@@ -0,0 +1 @@
+uv==0.11.28
diff --git a/requirements/wheel.txt b/requirements/wheel.txt
deleted file mode 100644
index ee8fec0fb..000000000
--- a/requirements/wheel.txt
+++ /dev/null
@@ -1 +0,0 @@
-wheel==0.43.0
diff --git a/spec/fixtures/ci_pip/.python-version b/spec/fixtures/ci_pip/.python-version
new file mode 100644
index 000000000..6324d401a
--- /dev/null
+++ b/spec/fixtures/ci_pip/.python-version
@@ -0,0 +1 @@
+3.14
diff --git a/spec/fixtures/ci_requirements/app.json b/spec/fixtures/ci_pip/app.json
similarity index 54%
rename from spec/fixtures/ci_requirements/app.json
rename to spec/fixtures/ci_pip/app.json
index 99d1d237f..59617c169 100644
--- a/spec/fixtures/ci_requirements/app.json
+++ b/spec/fixtures/ci_pip/app.json
@@ -2,7 +2,7 @@
   "environments": {
     "test": {
       "scripts": {
-        "test": "pytest --version"
+        "test": "./bin/print-env-vars.sh && pytest --version"
       }
     }
   }
diff --git a/spec/fixtures/ci_pip/bin/compile b/spec/fixtures/ci_pip/bin/compile
new file mode 100755
index 000000000..fcb7055e3
--- /dev/null
+++ b/spec/fixtures/ci_pip/bin/compile
@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack, and tests that the environment is
+# configured as expected for buildpacks that run after the Python buildpack.
+
+set -euo pipefail
+
+BUILD_DIR="${1}"
+
+cd "${BUILD_DIR}"
+
+exec bin/print-env-vars.sh
diff --git a/spec/fixtures/requirements_editable/bin/detect b/spec/fixtures/ci_pip/bin/detect
similarity index 100%
rename from spec/fixtures/requirements_editable/bin/detect
rename to spec/fixtures/ci_pip/bin/detect
diff --git a/spec/fixtures/ci_pip/bin/post_compile b/spec/fixtures/ci_pip/bin/post_compile
new file mode 100644
index 000000000..15dc8c2f3
--- /dev/null
+++ b/spec/fixtures/ci_pip/bin/post_compile
@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+# This intentionally uses a relative path to test that the CWD is correct.
+exec bin/print-env-vars.sh
diff --git a/spec/fixtures/ci_pip/bin/print-env-vars.sh b/spec/fixtures/ci_pip/bin/print-env-vars.sh
new file mode 100755
index 000000000..6cc32b420
--- /dev/null
+++ b/spec/fixtures/ci_pip/bin/print-env-vars.sh
@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+printenv | sort | grep -vE '^(_|BUILDPACK_LOG_FILE|CI_NODE_.+|DYNO|HEROKU_TEST_RUN_.+|HOME|OLDPWD|PORT|PWD|SHLVL|STACK|TERM)='
diff --git a/spec/fixtures/ci_pip/requirements-test.txt b/spec/fixtures/ci_pip/requirements-test.txt
new file mode 100644
index 000000000..d197ada2f
--- /dev/null
+++ b/spec/fixtures/ci_pip/requirements-test.txt
@@ -0,0 +1 @@
+pytest==8.3.4
diff --git a/spec/fixtures/ci_pip/requirements.txt b/spec/fixtures/ci_pip/requirements.txt
new file mode 100644
index 000000000..f6e499a84
--- /dev/null
+++ b/spec/fixtures/ci_pip/requirements.txt
@@ -0,0 +1,2 @@
+# This package has been picked since it has no dependencies and is small/fast to install.
+typing-extensions==4.15.0
diff --git a/spec/fixtures/ci_pipenv/.python-version b/spec/fixtures/ci_pipenv/.python-version
new file mode 100644
index 000000000..6324d401a
--- /dev/null
+++ b/spec/fixtures/ci_pipenv/.python-version
@@ -0,0 +1 @@
+3.14
diff --git a/spec/fixtures/pipenv_python_3.6/Pipfile b/spec/fixtures/ci_pipenv/Pipfile
similarity index 67%
rename from spec/fixtures/pipenv_python_3.6/Pipfile
rename to spec/fixtures/ci_pipenv/Pipfile
index 62a39bb91..6d6473eb4 100644
--- a/spec/fixtures/pipenv_python_3.6/Pipfile
+++ b/spec/fixtures/ci_pipenv/Pipfile
@@ -4,9 +4,7 @@ verify_ssl = true
 name = "pypi"
 
 [packages]
-urllib3 = "*"
+typing-extensions = "*"
 
 [dev-packages]
-
-[requires]
-python_version = "3.6"
+pytest = "*"
diff --git a/spec/fixtures/ci_pipenv/Pipfile.lock b/spec/fixtures/ci_pipenv/Pipfile.lock
new file mode 100644
index 000000000..f86d87a9d
--- /dev/null
+++ b/spec/fixtures/ci_pipenv/Pipfile.lock
@@ -0,0 +1,70 @@
+{
+    "_meta": {
+        "hash": {
+            "sha256": "9ac30f761973e7bb9a0425635eb284370fede0e49a74b475c418f98bf13f3075"
+        },
+        "pipfile-spec": 6,
+        "requires": {},
+        "sources": [
+            {
+                "name": "pypi",
+                "url": "https://pypi.org/simple",
+                "verify_ssl": true
+            }
+        ]
+    },
+    "default": {
+        "typing-extensions": {
+            "hashes": [
+                "sha256:0cea48d173cc12fa28ecabc3b837ea3cf6f38c6d1136f85cbaaf598984861466",
+                "sha256:f0fa19c6845758ab08074a0cfa8b7aecb71c999ca73d62883bc25cc018c4e548"
+            ],
+            "index": "pypi",
+            "markers": "python_version >= '3.9'",
+            "version": "==4.15.0"
+        }
+    },
+    "develop": {
+        "iniconfig": {
+            "hashes": [
+                "sha256:c76315c77db068650d49c5b56314774a7804df16fee4402c1f19d6d15d8c4730",
+                "sha256:f631c04d2c48c52b84d0d0549c99ff3859c98df65b3101406327ecc7d53fbf12"
+            ],
+            "markers": "python_version >= '3.10'",
+            "version": "==2.3.0"
+        },
+        "packaging": {
+            "hashes": [
+                "sha256:29572ef2b1f17581046b3a2227d5c611fb25ec70ca1ba8554b24b0e69331a484",
+                "sha256:d443872c98d677bf60f6a1f2f8c1cb748e8fe762d2bf9d3148b5599295b0fc4f"
+            ],
+            "markers": "python_version >= '3.8'",
+            "version": "==25.0"
+        },
+        "pluggy": {
+            "hashes": [
+                "sha256:7dcc130b76258d33b90f61b658791dede3486c3e6bfb003ee5c9bfb396dd22f3",
+                "sha256:e920276dd6813095e9377c0bc5566d94c932c33b27a3e3945d8389c374dd4746"
+            ],
+            "markers": "python_version >= '3.9'",
+            "version": "==1.6.0"
+        },
+        "pygments": {
+            "hashes": [
+                "sha256:636cb2477cec7f8952536970bc533bc43743542f70392ae026374600add5b887",
+                "sha256:86540386c03d588bb81d44bc3928634ff26449851e99741617ecb9037ee5ec0b"
+            ],
+            "markers": "python_version >= '3.8'",
+            "version": "==2.19.2"
+        },
+        "pytest": {
+            "hashes": [
+                "sha256:3e9c069ea73583e255c3b21cf46b8d3c56f6e3a1a8f6da94ccb0fcf57b9d73c8",
+                "sha256:67be0030d194df2dfa7b556f2e56fb3c3315bd5c8822c6951162b92b32ce7dad"
+            ],
+            "index": "pypi",
+            "markers": "python_version >= '3.10'",
+            "version": "==9.0.1"
+        }
+    }
+}
diff --git a/spec/fixtures/ci_pipenv/app.json b/spec/fixtures/ci_pipenv/app.json
new file mode 100644
index 000000000..59617c169
--- /dev/null
+++ b/spec/fixtures/ci_pipenv/app.json
@@ -0,0 +1,9 @@
+{
+  "environments": {
+    "test": {
+      "scripts": {
+        "test": "./bin/print-env-vars.sh && pytest --version"
+      }
+    }
+  }
+}
diff --git a/spec/fixtures/ci_pipenv/bin/compile b/spec/fixtures/ci_pipenv/bin/compile
new file mode 100755
index 000000000..fcb7055e3
--- /dev/null
+++ b/spec/fixtures/ci_pipenv/bin/compile
@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack, and tests that the environment is
+# configured as expected for buildpacks that run after the Python buildpack.
+
+set -euo pipefail
+
+BUILD_DIR="${1}"
+
+cd "${BUILD_DIR}"
+
+exec bin/print-env-vars.sh
diff --git a/spec/fixtures/ci_pipenv/bin/detect b/spec/fixtures/ci_pipenv/bin/detect
new file mode 100755
index 000000000..68cdcc4a2
--- /dev/null
+++ b/spec/fixtures/ci_pipenv/bin/detect
@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack.
+
+set -euo pipefail
+
+echo "Inline"
diff --git a/spec/fixtures/ci_pipenv/bin/post_compile b/spec/fixtures/ci_pipenv/bin/post_compile
new file mode 100644
index 000000000..15dc8c2f3
--- /dev/null
+++ b/spec/fixtures/ci_pipenv/bin/post_compile
@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+# This intentionally uses a relative path to test that the CWD is correct.
+exec bin/print-env-vars.sh
diff --git a/spec/fixtures/ci_pipenv/bin/print-env-vars.sh b/spec/fixtures/ci_pipenv/bin/print-env-vars.sh
new file mode 100755
index 000000000..6cc32b420
--- /dev/null
+++ b/spec/fixtures/ci_pipenv/bin/print-env-vars.sh
@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+printenv | sort | grep -vE '^(_|BUILDPACK_LOG_FILE|CI_NODE_.+|DYNO|HEROKU_TEST_RUN_.+|HOME|OLDPWD|PORT|PWD|SHLVL|STACK|TERM)='
diff --git a/spec/fixtures/ci_poetry/.python-version b/spec/fixtures/ci_poetry/.python-version
new file mode 100644
index 000000000..6324d401a
--- /dev/null
+++ b/spec/fixtures/ci_poetry/.python-version
@@ -0,0 +1 @@
+3.14
diff --git a/spec/fixtures/ci_poetry/app.json b/spec/fixtures/ci_poetry/app.json
new file mode 100644
index 000000000..59617c169
--- /dev/null
+++ b/spec/fixtures/ci_poetry/app.json
@@ -0,0 +1,9 @@
+{
+  "environments": {
+    "test": {
+      "scripts": {
+        "test": "./bin/print-env-vars.sh && pytest --version"
+      }
+    }
+  }
+}
diff --git a/spec/fixtures/ci_poetry/bin/compile b/spec/fixtures/ci_poetry/bin/compile
new file mode 100755
index 000000000..fcb7055e3
--- /dev/null
+++ b/spec/fixtures/ci_poetry/bin/compile
@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack, and tests that the environment is
+# configured as expected for buildpacks that run after the Python buildpack.
+
+set -euo pipefail
+
+BUILD_DIR="${1}"
+
+cd "${BUILD_DIR}"
+
+exec bin/print-env-vars.sh
diff --git a/spec/fixtures/ci_poetry/bin/detect b/spec/fixtures/ci_poetry/bin/detect
new file mode 100755
index 000000000..68cdcc4a2
--- /dev/null
+++ b/spec/fixtures/ci_poetry/bin/detect
@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack.
+
+set -euo pipefail
+
+echo "Inline"
diff --git a/spec/fixtures/ci_poetry/bin/post_compile b/spec/fixtures/ci_poetry/bin/post_compile
new file mode 100644
index 000000000..15dc8c2f3
--- /dev/null
+++ b/spec/fixtures/ci_poetry/bin/post_compile
@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+# This intentionally uses a relative path to test that the CWD is correct.
+exec bin/print-env-vars.sh
diff --git a/spec/fixtures/ci_poetry/bin/print-env-vars.sh b/spec/fixtures/ci_poetry/bin/print-env-vars.sh
new file mode 100755
index 000000000..6cc32b420
--- /dev/null
+++ b/spec/fixtures/ci_poetry/bin/print-env-vars.sh
@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+printenv | sort | grep -vE '^(_|BUILDPACK_LOG_FILE|CI_NODE_.+|DYNO|HEROKU_TEST_RUN_.+|HOME|OLDPWD|PORT|PWD|SHLVL|STACK|TERM)='
diff --git a/spec/fixtures/ci_poetry/poetry.lock b/spec/fixtures/ci_poetry/poetry.lock
new file mode 100644
index 000000000..51cc64181
--- /dev/null
+++ b/spec/fixtures/ci_poetry/poetry.lock
@@ -0,0 +1,108 @@
+# This file is automatically @generated by Poetry 2.2.1 and should not be changed by hand.
+
+[[package]]
+name = "colorama"
+version = "0.4.6"
+description = "Cross-platform colored terminal text."
+optional = false
+python-versions = "!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*,!=3.5.*,!=3.6.*,>=2.7"
+groups = ["dev"]
+markers = "sys_platform == \"win32\""
+files = [
+    {file = "colorama-0.4.6-py2.py3-none-any.whl", hash = "sha256:4f1d9991f5acc0ca119f9d443620b77f9d6b33703e51011c16baf57afb285fc6"},
+    {file = "colorama-0.4.6.tar.gz", hash = "sha256:08695f5cb7ed6e0531a20572697297273c47b8cae5a63ffc6d6ed5c201be6e44"},
+]
+
+[[package]]
+name = "iniconfig"
+version = "2.3.0"
+description = "brain-dead simple config-ini parsing"
+optional = false
+python-versions = ">=3.10"
+groups = ["dev"]
+files = [
+    {file = "iniconfig-2.3.0-py3-none-any.whl", hash = "sha256:f631c04d2c48c52b84d0d0549c99ff3859c98df65b3101406327ecc7d53fbf12"},
+    {file = "iniconfig-2.3.0.tar.gz", hash = "sha256:c76315c77db068650d49c5b56314774a7804df16fee4402c1f19d6d15d8c4730"},
+]
+
+[[package]]
+name = "packaging"
+version = "25.0"
+description = "Core utilities for Python packages"
+optional = false
+python-versions = ">=3.8"
+groups = ["dev"]
+files = [
+    {file = "packaging-25.0-py3-none-any.whl", hash = "sha256:29572ef2b1f17581046b3a2227d5c611fb25ec70ca1ba8554b24b0e69331a484"},
+    {file = "packaging-25.0.tar.gz", hash = "sha256:d443872c98d677bf60f6a1f2f8c1cb748e8fe762d2bf9d3148b5599295b0fc4f"},
+]
+
+[[package]]
+name = "pluggy"
+version = "1.6.0"
+description = "plugin and hook calling mechanisms for python"
+optional = false
+python-versions = ">=3.9"
+groups = ["dev"]
+files = [
+    {file = "pluggy-1.6.0-py3-none-any.whl", hash = "sha256:e920276dd6813095e9377c0bc5566d94c932c33b27a3e3945d8389c374dd4746"},
+    {file = "pluggy-1.6.0.tar.gz", hash = "sha256:7dcc130b76258d33b90f61b658791dede3486c3e6bfb003ee5c9bfb396dd22f3"},
+]
+
+[package.extras]
+dev = ["pre-commit", "tox"]
+testing = ["coverage", "pytest", "pytest-benchmark"]
+
+[[package]]
+name = "pygments"
+version = "2.19.2"
+description = "Pygments is a syntax highlighting package written in Python."
+optional = false
+python-versions = ">=3.8"
+groups = ["dev"]
+files = [
+    {file = "pygments-2.19.2-py3-none-any.whl", hash = "sha256:86540386c03d588bb81d44bc3928634ff26449851e99741617ecb9037ee5ec0b"},
+    {file = "pygments-2.19.2.tar.gz", hash = "sha256:636cb2477cec7f8952536970bc533bc43743542f70392ae026374600add5b887"},
+]
+
+[package.extras]
+windows-terminal = ["colorama (>=0.4.6)"]
+
+[[package]]
+name = "pytest"
+version = "9.0.1"
+description = "pytest: simple powerful testing with Python"
+optional = false
+python-versions = ">=3.10"
+groups = ["dev"]
+files = [
+    {file = "pytest-9.0.1-py3-none-any.whl", hash = "sha256:67be0030d194df2dfa7b556f2e56fb3c3315bd5c8822c6951162b92b32ce7dad"},
+    {file = "pytest-9.0.1.tar.gz", hash = "sha256:3e9c069ea73583e255c3b21cf46b8d3c56f6e3a1a8f6da94ccb0fcf57b9d73c8"},
+]
+
+[package.dependencies]
+colorama = {version = ">=0.4", markers = "sys_platform == \"win32\""}
+iniconfig = ">=1.0.1"
+packaging = ">=22"
+pluggy = ">=1.5,<2"
+pygments = ">=2.7.2"
+
+[package.extras]
+dev = ["argcomplete", "attrs (>=19.2)", "hypothesis (>=3.56)", "mock", "requests", "setuptools", "xmlschema"]
+
+[[package]]
+name = "typing-extensions"
+version = "4.15.0"
+description = "Backported and Experimental Type Hints for Python 3.9+"
+optional = false
+python-versions = ">=3.9"
+groups = ["main"]
+files = [
+    {file = "typing_extensions-4.15.0-py3-none-any.whl", hash = "sha256:f0fa19c6845758ab08074a0cfa8b7aecb71c999ca73d62883bc25cc018c4e548"},
+    {file = "typing_extensions-4.15.0.tar.gz", hash = "sha256:0cea48d173cc12fa28ecabc3b837ea3cf6f38c6d1136f85cbaaf598984861466"},
+]
+
+[metadata]
+lock-version = "2.1"
+python-versions = ">=3.14"
+content-hash = "a0f8d6facd04ce28abc860e56bb4af6e1acac71a1f2a93e4e6ed4e13a299e055"
diff --git a/spec/fixtures/ci_poetry/pyproject.toml b/spec/fixtures/ci_poetry/pyproject.toml
new file mode 100644
index 000000000..161499343
--- /dev/null
+++ b/spec/fixtures/ci_poetry/pyproject.toml
@@ -0,0 +1,16 @@
+[project]
+name = "ci-poetry"
+version = "0.0.0"
+requires-python = ">=3.14"
+dependencies = [
+    "typing-extensions",
+]
+
+[dependency-groups]
+dev = [
+    "pytest",
+]
+
+
+[tool.poetry]
+package-mode = false
diff --git a/spec/fixtures/ci_requirements/requirements-test.txt b/spec/fixtures/ci_requirements/requirements-test.txt
deleted file mode 100644
index e079f8a60..000000000
--- a/spec/fixtures/ci_requirements/requirements-test.txt
+++ /dev/null
@@ -1 +0,0 @@
-pytest
diff --git a/spec/fixtures/ci_requirements/requirements.txt b/spec/fixtures/ci_requirements/requirements.txt
deleted file mode 100644
index a42590beb..000000000
--- a/spec/fixtures/ci_requirements/requirements.txt
+++ /dev/null
@@ -1 +0,0 @@
-urllib3
diff --git a/spec/fixtures/ci_uv/.python-version b/spec/fixtures/ci_uv/.python-version
new file mode 100644
index 000000000..6324d401a
--- /dev/null
+++ b/spec/fixtures/ci_uv/.python-version
@@ -0,0 +1 @@
+3.14
diff --git a/spec/fixtures/ci_uv/app.json b/spec/fixtures/ci_uv/app.json
new file mode 100644
index 000000000..59617c169
--- /dev/null
+++ b/spec/fixtures/ci_uv/app.json
@@ -0,0 +1,9 @@
+{
+  "environments": {
+    "test": {
+      "scripts": {
+        "test": "./bin/print-env-vars.sh && pytest --version"
+      }
+    }
+  }
+}
diff --git a/spec/fixtures/ci_uv/bin/compile b/spec/fixtures/ci_uv/bin/compile
new file mode 100755
index 000000000..fcb7055e3
--- /dev/null
+++ b/spec/fixtures/ci_uv/bin/compile
@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack, and tests that the environment is
+# configured as expected for buildpacks that run after the Python buildpack.
+
+set -euo pipefail
+
+BUILD_DIR="${1}"
+
+cd "${BUILD_DIR}"
+
+exec bin/print-env-vars.sh
diff --git a/spec/fixtures/ci_uv/bin/detect b/spec/fixtures/ci_uv/bin/detect
new file mode 100755
index 000000000..68cdcc4a2
--- /dev/null
+++ b/spec/fixtures/ci_uv/bin/detect
@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack.
+
+set -euo pipefail
+
+echo "Inline"
diff --git a/spec/fixtures/ci_uv/bin/post_compile b/spec/fixtures/ci_uv/bin/post_compile
new file mode 100644
index 000000000..15dc8c2f3
--- /dev/null
+++ b/spec/fixtures/ci_uv/bin/post_compile
@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+# This intentionally uses a relative path to test that the CWD is correct.
+exec bin/print-env-vars.sh
diff --git a/spec/fixtures/ci_uv/bin/print-env-vars.sh b/spec/fixtures/ci_uv/bin/print-env-vars.sh
new file mode 100755
index 000000000..6cc32b420
--- /dev/null
+++ b/spec/fixtures/ci_uv/bin/print-env-vars.sh
@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+printenv | sort | grep -vE '^(_|BUILDPACK_LOG_FILE|CI_NODE_.+|DYNO|HEROKU_TEST_RUN_.+|HOME|OLDPWD|PORT|PWD|SHLVL|STACK|TERM)='
diff --git a/spec/fixtures/ci_uv/pyproject.toml b/spec/fixtures/ci_uv/pyproject.toml
new file mode 100644
index 000000000..443befffc
--- /dev/null
+++ b/spec/fixtures/ci_uv/pyproject.toml
@@ -0,0 +1,12 @@
+[project]
+name = "ci-uv"
+version = "0.0.0"
+requires-python = ">=3.14"
+dependencies = [
+    "typing-extensions",
+]
+
+[dependency-groups]
+dev = [
+    "pytest",
+]
diff --git a/spec/fixtures/ci_uv/uv.lock b/spec/fixtures/ci_uv/uv.lock
new file mode 100644
index 000000000..da352f67b
--- /dev/null
+++ b/spec/fixtures/ci_uv/uv.lock
@@ -0,0 +1,92 @@
+version = 1
+revision = 3
+requires-python = ">=3.14"
+
+[[package]]
+name = "ci-uv"
+version = "0.0.0"
+source = { virtual = "." }
+dependencies = [
+    { name = "typing-extensions" },
+]
+
+[package.dev-dependencies]
+dev = [
+    { name = "pytest" },
+]
+
+[package.metadata]
+requires-dist = [{ name = "typing-extensions" }]
+
+[package.metadata.requires-dev]
+dev = [{ name = "pytest" }]
+
+[[package]]
+name = "colorama"
+version = "0.4.6"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/d8/53/6f443c9a4a8358a93a6792e2acffb9d9d5cb0a5cfd8802644b7b1c9a02e4/colorama-0.4.6.tar.gz", hash = "sha256:08695f5cb7ed6e0531a20572697297273c47b8cae5a63ffc6d6ed5c201be6e44", size = 27697, upload-time = "2022-10-25T02:36:22.414Z" }
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+]
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+[[package]]
+name = "iniconfig"
+version = "2.3.0"
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+]
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+[[package]]
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+wheels = [
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+wheels = [
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+]
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+[[package]]
+name = "pytest"
+version = "9.0.1"
+source = { registry = "https://pypi.org/simple" }
+dependencies = [
+    { name = "colorama", marker = "sys_platform == 'win32'" },
+    { name = "iniconfig" },
+    { name = "packaging" },
+    { name = "pluggy" },
+    { name = "pygments" },
+]
+sdist = { url = "https://files.pythonhosted.org/packages/07/56/f013048ac4bc4c1d9be45afd4ab209ea62822fb1598f40687e6bf45dcea4/pytest-9.0.1.tar.gz", hash = "sha256:3e9c069ea73583e255c3b21cf46b8d3c56f6e3a1a8f6da94ccb0fcf57b9d73c8", size = 1564125, upload-time = "2025-11-12T13:05:09.333Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/0b/8b/6300fb80f858cda1c51ffa17075df5d846757081d11ab4aa35cef9e6258b/pytest-9.0.1-py3-none-any.whl", hash = "sha256:67be0030d194df2dfa7b556f2e56fb3c3315bd5c8822c6951162b92b32ce7dad", size = 373668, upload-time = "2025-11-12T13:05:07.379Z" },
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+[[package]]
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+source = { registry = "https://pypi.org/simple" }
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+wheels = [
+    { url = "https://files.pythonhosted.org/packages/18/67/36e9267722cc04a6b9f15c7f3441c2363321a3ea07da7ae0c0707beb2a9c/typing_extensions-4.15.0-py3-none-any.whl", hash = "sha256:f0fa19c6845758ab08074a0cfa8b7aecb71c999ca73d62883bc25cc018c4e548", size = 44614, upload-time = "2025-08-25T13:49:24.86Z" },
+]
diff --git a/spec/fixtures/django_collectstatic_disabled_file/manage.py b/spec/fixtures/django_collectstatic_disabled_file/manage.py
new file mode 100644
index 000000000..5ed9a654d
--- /dev/null
+++ b/spec/fixtures/django_collectstatic_disabled_file/manage.py
@@ -0,0 +1,22 @@
+#!/usr/bin/env python
+"""Django's command-line utility for administrative tasks."""
+import os
+import sys
+
+
+def main():
+    """Run administrative tasks."""
+    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "nonexistent-module.settings")
+    try:
+        from django.core.management import execute_from_command_line
+    except ImportError as exc:
+        raise ImportError(
+            "Couldn't import Django. Are you sure it's installed and "
+            "available on your PYTHONPATH environment variable? Did you "
+            "forget to activate a virtual environment?"
+        ) from exc
+    execute_from_command_line(sys.argv)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/spec/fixtures/django_invalid_settings_module/manage.py b/spec/fixtures/django_invalid_settings_module/manage.py
new file mode 100644
index 000000000..5ed9a654d
--- /dev/null
+++ b/spec/fixtures/django_invalid_settings_module/manage.py
@@ -0,0 +1,22 @@
+#!/usr/bin/env python
+"""Django's command-line utility for administrative tasks."""
+import os
+import sys
+
+
+def main():
+    """Run administrative tasks."""
+    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "nonexistent-module.settings")
+    try:
+        from django.core.management import execute_from_command_line
+    except ImportError as exc:
+        raise ImportError(
+            "Couldn't import Django. Are you sure it's installed and "
+            "available on your PYTHONPATH environment variable? Did you "
+            "forget to activate a virtual environment?"
+        ) from exc
+    execute_from_command_line(sys.argv)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/spec/fixtures/django_broken_project/requirements.txt b/spec/fixtures/django_invalid_settings_module/requirements.txt
similarity index 100%
rename from spec/fixtures/django_broken_project/requirements.txt
rename to spec/fixtures/django_invalid_settings_module/requirements.txt
diff --git a/spec/fixtures/requirements_django_latest/requirements.txt b/spec/fixtures/django_no_manage_py/requirements.txt
similarity index 100%
rename from spec/fixtures/requirements_django_latest/requirements.txt
rename to spec/fixtures/django_no_manage_py/requirements.txt
diff --git a/spec/fixtures/django_staticfiles_app_not_enabled/manage.py b/spec/fixtures/django_staticfiles_app_not_enabled/manage.py
new file mode 100644
index 000000000..8bd034f0d
--- /dev/null
+++ b/spec/fixtures/django_staticfiles_app_not_enabled/manage.py
@@ -0,0 +1,22 @@
+#!/usr/bin/env python
+"""Django's command-line utility for administrative tasks."""
+import os
+import sys
+
+
+def main():
+    """Run administrative tasks."""
+    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "testproject.settings")
+    try:
+        from django.core.management import execute_from_command_line
+    except ImportError as exc:
+        raise ImportError(
+            "Couldn't import Django. Are you sure it's installed and "
+            "available on your PYTHONPATH environment variable? Did you "
+            "forget to activate a virtual environment?"
+        ) from exc
+    execute_from_command_line(sys.argv)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/spec/fixtures/django_staticfiles_app_not_enabled/requirements.txt b/spec/fixtures/django_staticfiles_app_not_enabled/requirements.txt
new file mode 100644
index 000000000..94a0e8344
--- /dev/null
+++ b/spec/fixtures/django_staticfiles_app_not_enabled/requirements.txt
@@ -0,0 +1 @@
+Django
diff --git a/spec/fixtures/hooks/requirements.txt b/spec/fixtures/django_staticfiles_app_not_enabled/testproject/__init__.py
similarity index 100%
rename from spec/fixtures/hooks/requirements.txt
rename to spec/fixtures/django_staticfiles_app_not_enabled/testproject/__init__.py
diff --git a/spec/fixtures/django_staticfiles_app_not_enabled/testproject/settings.py b/spec/fixtures/django_staticfiles_app_not_enabled/testproject/settings.py
new file mode 100644
index 000000000..5922fd00c
--- /dev/null
+++ b/spec/fixtures/django_staticfiles_app_not_enabled/testproject/settings.py
@@ -0,0 +1,15 @@
+from pathlib import Path
+
+BASE_DIR = Path(__file__).resolve().parent.parent
+
+INSTALLED_APPS = [
+    "django.contrib.auth",
+    "django.contrib.contenttypes",
+    "django.contrib.sessions",
+    "django.contrib.messages",
+    # The staticfiles app (which is what provides the collectstatic command) is not enabled.
+    # "django.contrib.staticfiles",
+]
+
+STATIC_ROOT = BASE_DIR / "staticfiles"
+STATIC_URL = "static/"
diff --git a/spec/fixtures/django_staticfiles_latest_django/backend/manage.py b/spec/fixtures/django_staticfiles_latest_django/backend/manage.py
new file mode 100644
index 000000000..8bd034f0d
--- /dev/null
+++ b/spec/fixtures/django_staticfiles_latest_django/backend/manage.py
@@ -0,0 +1,22 @@
+#!/usr/bin/env python
+"""Django's command-line utility for administrative tasks."""
+import os
+import sys
+
+
+def main():
+    """Run administrative tasks."""
+    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "testproject.settings")
+    try:
+        from django.core.management import execute_from_command_line
+    except ImportError as exc:
+        raise ImportError(
+            "Couldn't import Django. Are you sure it's installed and "
+            "available on your PYTHONPATH environment variable? Did you "
+            "forget to activate a virtual environment?"
+        ) from exc
+    execute_from_command_line(sys.argv)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/spec/fixtures/django_staticfiles_latest_django/backend/requirements.txt b/spec/fixtures/django_staticfiles_latest_django/backend/requirements.txt
new file mode 100644
index 000000000..94a0e8344
--- /dev/null
+++ b/spec/fixtures/django_staticfiles_latest_django/backend/requirements.txt
@@ -0,0 +1 @@
+Django
diff --git a/spec/fixtures/python_3.10_outdated/requirements.txt b/spec/fixtures/django_staticfiles_latest_django/backend/testapp/__init__.py
similarity index 100%
rename from spec/fixtures/python_3.10_outdated/requirements.txt
rename to spec/fixtures/django_staticfiles_latest_django/backend/testapp/__init__.py
diff --git a/spec/fixtures/python_3.11_outdated/requirements.txt b/spec/fixtures/django_staticfiles_latest_django/backend/testapp/static/robots.txt
similarity index 100%
rename from spec/fixtures/python_3.11_outdated/requirements.txt
rename to spec/fixtures/django_staticfiles_latest_django/backend/testapp/static/robots.txt
diff --git a/spec/fixtures/python_3.12_outdated/requirements.txt b/spec/fixtures/django_staticfiles_latest_django/backend/testproject/__init__.py
similarity index 100%
rename from spec/fixtures/python_3.12_outdated/requirements.txt
rename to spec/fixtures/django_staticfiles_latest_django/backend/testproject/__init__.py
diff --git a/spec/fixtures/django_staticfiles_latest_django/backend/testproject/settings.py b/spec/fixtures/django_staticfiles_latest_django/backend/testproject/settings.py
new file mode 100644
index 000000000..91b07ab13
--- /dev/null
+++ b/spec/fixtures/django_staticfiles_latest_django/backend/testproject/settings.py
@@ -0,0 +1,32 @@
+import os
+import sys
+from pathlib import Path
+from pprint import pprint
+
+BASE_DIR = Path(__file__).resolve().parent.parent
+
+INSTALLED_APPS = [
+    "django.contrib.staticfiles",
+    "testapp",
+]
+
+STATIC_ROOT = BASE_DIR / "staticfiles"
+STATIC_URL = "static/"
+
+ENV_VARS_TO_OMIT = {
+    "_",
+    "BUILDPACK_LOG_FILE",
+    "DYNO",
+    "HOME",
+    "OLDPWD",
+    "REQUEST_ID",
+    "SHLVL",
+    "SOURCE_VERSION",
+    "STACK",
+}
+pprint({k: v for k, v in os.environ.items() if k not in ENV_VARS_TO_OMIT})
+print()
+pprint(sys.path)
+
+# Tests that app env vars are passed to the 'manage.py' script invocations.
+assert "EXPECTED_ENV_VAR" in os.environ
diff --git a/spec/fixtures/django_staticfiles_latest_django/requirements.txt b/spec/fixtures/django_staticfiles_latest_django/requirements.txt
new file mode 120000
index 000000000..ed17bf41b
--- /dev/null
+++ b/spec/fixtures/django_staticfiles_latest_django/requirements.txt
@@ -0,0 +1 @@
+backend/requirements.txt
\ No newline at end of file
diff --git a/spec/fixtures/django_staticfiles_legacy_django/.python-version b/spec/fixtures/django_staticfiles_legacy_django/.python-version
new file mode 100644
index 000000000..c8cfe3959
--- /dev/null
+++ b/spec/fixtures/django_staticfiles_legacy_django/.python-version
@@ -0,0 +1 @@
+3.10
diff --git a/spec/fixtures/django_broken_project/manage.py b/spec/fixtures/django_staticfiles_legacy_django/manage.py
similarity index 69%
rename from spec/fixtures/django_broken_project/manage.py
rename to spec/fixtures/django_staticfiles_legacy_django/manage.py
index eb3ab8af5..97ed576b6 100644
--- a/spec/fixtures/django_broken_project/manage.py
+++ b/spec/fixtures/django_staticfiles_legacy_django/manage.py
@@ -3,7 +3,7 @@
 import sys
 
 if __name__ == "__main__":
-    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "gettingstarted.settings")
+    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "testproject.settings")
 
     from django.core.management import execute_from_command_line
 
diff --git a/spec/fixtures/django_staticfiles_legacy_django/requirements.txt b/spec/fixtures/django_staticfiles_legacy_django/requirements.txt
new file mode 100644
index 000000000..7f5462e9c
--- /dev/null
+++ b/spec/fixtures/django_staticfiles_legacy_django/requirements.txt
@@ -0,0 +1,2 @@
+# This is the oldest Django version that works on Python 3.10 (our oldest supported Python version).
+Django==2.1.15
diff --git a/spec/fixtures/python_3.8_outdated/requirements.txt b/spec/fixtures/django_staticfiles_legacy_django/testapp/__init__.py
similarity index 100%
rename from spec/fixtures/python_3.8_outdated/requirements.txt
rename to spec/fixtures/django_staticfiles_legacy_django/testapp/__init__.py
diff --git a/spec/fixtures/python_3.9_outdated/requirements.txt b/spec/fixtures/django_staticfiles_legacy_django/testapp/static/robots.txt
similarity index 100%
rename from spec/fixtures/python_3.9_outdated/requirements.txt
rename to spec/fixtures/django_staticfiles_legacy_django/testapp/static/robots.txt
diff --git a/spec/fixtures/python_version_invalid/requirements.txt b/spec/fixtures/django_staticfiles_legacy_django/testproject/__init__.py
similarity index 100%
rename from spec/fixtures/python_version_invalid/requirements.txt
rename to spec/fixtures/django_staticfiles_legacy_django/testproject/__init__.py
diff --git a/spec/fixtures/django_staticfiles_legacy_django/testproject/settings.py b/spec/fixtures/django_staticfiles_legacy_django/testproject/settings.py
new file mode 100644
index 000000000..ad916f8e8
--- /dev/null
+++ b/spec/fixtures/django_staticfiles_legacy_django/testproject/settings.py
@@ -0,0 +1,35 @@
+import os
+import sys
+from pathlib import Path
+from pprint import pprint
+
+BASE_DIR = Path(__file__).resolve().parent.parent
+
+INSTALLED_APPS = [
+    "django.contrib.staticfiles",
+    "testapp",
+]
+
+STATIC_ROOT = BASE_DIR / "staticfiles"
+STATIC_URL = "static/"
+
+# Older versions of Django require that `SECRET_KEY` is set when running collectstatic.
+SECRET_KEY = "example"
+
+ENV_VARS_TO_OMIT = {
+    "_",
+    "BUILDPACK_LOG_FILE",
+    "DYNO",
+    "HOME",
+    "OLDPWD",
+    "REQUEST_ID",
+    "SHLVL",
+    "SOURCE_VERSION",
+    "STACK",
+}
+pprint({k: v for k, v in os.environ.items() if k not in ENV_VARS_TO_OMIT})
+print()
+pprint(sys.path)
+
+# Tests that app env vars are passed to the 'manage.py' script invocations.
+assert "EXPECTED_ENV_VAR" in os.environ
diff --git a/spec/fixtures/django_staticfiles_misconfigured/manage.py b/spec/fixtures/django_staticfiles_misconfigured/manage.py
new file mode 100644
index 000000000..8bd034f0d
--- /dev/null
+++ b/spec/fixtures/django_staticfiles_misconfigured/manage.py
@@ -0,0 +1,22 @@
+#!/usr/bin/env python
+"""Django's command-line utility for administrative tasks."""
+import os
+import sys
+
+
+def main():
+    """Run administrative tasks."""
+    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "testproject.settings")
+    try:
+        from django.core.management import execute_from_command_line
+    except ImportError as exc:
+        raise ImportError(
+            "Couldn't import Django. Are you sure it's installed and "
+            "available on your PYTHONPATH environment variable? Did you "
+            "forget to activate a virtual environment?"
+        ) from exc
+    execute_from_command_line(sys.argv)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/spec/fixtures/django_staticfiles_misconfigured/requirements.txt b/spec/fixtures/django_staticfiles_misconfigured/requirements.txt
new file mode 100644
index 000000000..94a0e8344
--- /dev/null
+++ b/spec/fixtures/django_staticfiles_misconfigured/requirements.txt
@@ -0,0 +1 @@
+Django
diff --git a/spec/fixtures/runtime_txt_only/subdir/some-file b/spec/fixtures/django_staticfiles_misconfigured/testproject/__init__.py
similarity index 100%
rename from spec/fixtures/runtime_txt_only/subdir/some-file
rename to spec/fixtures/django_staticfiles_misconfigured/testproject/__init__.py
diff --git a/spec/fixtures/django_staticfiles_misconfigured/testproject/settings.py b/spec/fixtures/django_staticfiles_misconfigured/testproject/settings.py
new file mode 100644
index 000000000..1a521e130
--- /dev/null
+++ b/spec/fixtures/django_staticfiles_misconfigured/testproject/settings.py
@@ -0,0 +1,6 @@
+INSTALLED_APPS = [
+    "django.contrib.staticfiles",
+]
+
+# This is an invalid STATIC_ROOT value if collectstatic is being used.
+STATIC_ROOT = None
diff --git a/spec/fixtures/hooks/bin/post_compile b/spec/fixtures/hooks/bin/post_compile
deleted file mode 100644
index 373d33889..000000000
--- a/spec/fixtures/hooks/bin/post_compile
+++ /dev/null
@@ -1,6 +0,0 @@
-#!/usr/bin/env bash
-
-set -euo pipefail
-
-echo 'post_compile ran with env vars:'
-printenv | cut -d '=' -f 1 | sort
diff --git a/spec/fixtures/hooks/bin/pre_compile b/spec/fixtures/hooks/bin/pre_compile
deleted file mode 100644
index 40d1a402e..000000000
--- a/spec/fixtures/hooks/bin/pre_compile
+++ /dev/null
@@ -1,6 +0,0 @@
-#!/usr/bin/env bash
-
-set -euo pipefail
-
-echo 'pre_compile ran with env vars:'
-printenv | cut -d '=' -f 1 | sort
diff --git a/spec/fixtures/hooks_delete_cache_dir/bin/post_compile b/spec/fixtures/hooks_delete_cache_dir/bin/post_compile
new file mode 100644
index 000000000..383d0656b
--- /dev/null
+++ b/spec/fixtures/hooks_delete_cache_dir/bin/post_compile
@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+set -x
+rm -rf "${CACHE_DIR:?}"
diff --git a/spec/fixtures/hooks_delete_cache_dir/requirements.txt b/spec/fixtures/hooks_delete_cache_dir/requirements.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/hooks_pre_compile_fail/bin/pre_compile b/spec/fixtures/hooks_pre_compile_fail/bin/pre_compile
new file mode 100644
index 000000000..07e0236cf
--- /dev/null
+++ b/spec/fixtures/hooks_pre_compile_fail/bin/pre_compile
@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+echo 'Some pre_compile error!' >&2
+exit 1
diff --git a/spec/fixtures/hooks_pre_compile_fail/requirements.txt b/spec/fixtures/hooks_pre_compile_fail/requirements.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/hooks_pre_compile_pass_post_compile_fail/bin/post_compile b/spec/fixtures/hooks_pre_compile_pass_post_compile_fail/bin/post_compile
new file mode 100644
index 000000000..9cdc2b9a1
--- /dev/null
+++ b/spec/fixtures/hooks_pre_compile_pass_post_compile_fail/bin/post_compile
@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+echo 'Some post_compile error!' >&2
+exit 1
diff --git a/spec/fixtures/hooks_pre_compile_pass_post_compile_fail/bin/pre_compile b/spec/fixtures/hooks_pre_compile_pass_post_compile_fail/bin/pre_compile
new file mode 100644
index 000000000..d1401761e
--- /dev/null
+++ b/spec/fixtures/hooks_pre_compile_pass_post_compile_fail/bin/pre_compile
@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+echo '~ pre_compile ran with env vars:'
+printenv | sort | grep -vE '^(_|BUILDPACK_LOG_FILE|DYNO|HOME|OLDPWD|PWD|REQUEST_ID|SHLVL|SOURCE_VERSION|STACK)='
+echo '~ pre_compile complete'
diff --git a/spec/fixtures/hooks_pre_compile_pass_post_compile_fail/requirements.txt b/spec/fixtures/hooks_pre_compile_pass_post_compile_fail/requirements.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/multiple_package_managers/Pipfile b/spec/fixtures/multiple_package_managers/Pipfile
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/multiple_package_managers/Pipfile.lock b/spec/fixtures/multiple_package_managers/Pipfile.lock
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/multiple_package_managers/poetry.lock b/spec/fixtures/multiple_package_managers/poetry.lock
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/multiple_package_managers/pyproject.toml b/spec/fixtures/multiple_package_managers/pyproject.toml
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/multiple_package_managers/requirements.txt b/spec/fixtures/multiple_package_managers/requirements.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/multiple_package_managers/setup.py b/spec/fixtures/multiple_package_managers/setup.py
new file mode 100644
index 000000000..ab45d8b72
--- /dev/null
+++ b/spec/fixtures/multiple_package_managers/setup.py
@@ -0,0 +1 @@
+# This file tests that the setup.py sunset error is not shown when other package manager files exist.
diff --git a/spec/fixtures/multiple_package_managers/uv.lock b/spec/fixtures/multiple_package_managers/uv.lock
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/nltk_txt_invalid/nltk.txt b/spec/fixtures/nltk_txt_invalid/nltk.txt
new file mode 100644
index 000000000..719ce91ff
--- /dev/null
+++ b/spec/fixtures/nltk_txt_invalid/nltk.txt
@@ -0,0 +1 @@
+invalid!
diff --git a/spec/fixtures/nltk_txt_invalid/requirements.txt b/spec/fixtures/nltk_txt_invalid/requirements.txt
new file mode 100644
index 000000000..846929621
--- /dev/null
+++ b/spec/fixtures/nltk_txt_invalid/requirements.txt
@@ -0,0 +1 @@
+nltk
diff --git a/spec/fixtures/no_python_project_files/.example-dotfile b/spec/fixtures/no_python_project_files/.example-dotfile
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/pip_basic/.python-version b/spec/fixtures/pip_basic/.python-version
new file mode 100644
index 000000000..6324d401a
--- /dev/null
+++ b/spec/fixtures/pip_basic/.python-version
@@ -0,0 +1 @@
+3.14
diff --git a/spec/fixtures/pip_basic/bin/compile b/spec/fixtures/pip_basic/bin/compile
new file mode 100755
index 000000000..7d1d552df
--- /dev/null
+++ b/spec/fixtures/pip_basic/bin/compile
@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack, and tests that the environment is
+# configured as expected for buildpacks that run after the Python buildpack.
+
+set -euo pipefail
+
+BUILD_DIR="${1}"
+CACHE_DIR="${2}"
+
+cd "${BUILD_DIR}"
+
+bin/print-env-vars.sh
+echo
+
+python -c 'import pprint, sys; pprint.pp(sys.path)'
+echo
+
+pip --version
+pip list
+echo
+
+python -c 'import typing_extensions; print(typing_extensions)'
+echo
+
+jq --sort-keys '.' "${CACHE_DIR}/build-data/python.json"
diff --git a/spec/fixtures/pip_basic/bin/detect b/spec/fixtures/pip_basic/bin/detect
new file mode 100755
index 000000000..68cdcc4a2
--- /dev/null
+++ b/spec/fixtures/pip_basic/bin/detect
@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack.
+
+set -euo pipefail
+
+echo "Inline"
diff --git a/spec/fixtures/pip_basic/bin/post_compile b/spec/fixtures/pip_basic/bin/post_compile
new file mode 100644
index 000000000..15dc8c2f3
--- /dev/null
+++ b/spec/fixtures/pip_basic/bin/post_compile
@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+# This intentionally uses a relative path to test that the CWD is correct.
+exec bin/print-env-vars.sh
diff --git a/spec/fixtures/pip_basic/bin/print-env-vars.sh b/spec/fixtures/pip_basic/bin/print-env-vars.sh
new file mode 100755
index 000000000..ebc9ad735
--- /dev/null
+++ b/spec/fixtures/pip_basic/bin/print-env-vars.sh
@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+printenv | sort | grep -vE '^(_|BUILDPACK_LOG_FILE|DYNO|HOME|OLDPWD|PORT|PS1|PWD|REQUEST_ID|SHLVL|SOURCE_VERSION|STACK|TERM)='
diff --git a/spec/fixtures/pip_basic/cat b/spec/fixtures/pip_basic/cat
new file mode 100755
index 000000000..d213c595e
--- /dev/null
+++ b/spec/fixtures/pip_basic/cat
@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+
+echo "This custom script shouldn't take precedence over /usr/bin/cat!" >&2
+exit 1
diff --git a/spec/fixtures/pip_basic/manage.py b/spec/fixtures/pip_basic/manage.py
new file mode 100644
index 000000000..db7e7d588
--- /dev/null
+++ b/spec/fixtures/pip_basic/manage.py
@@ -0,0 +1,2 @@
+# Tests that manage.py alone doesn't trigger Django collectstatic.
+raise RuntimeError("This is not a Django app, so manage.py should not be run!")
diff --git a/spec/fixtures/pip_basic/requirements-test.txt b/spec/fixtures/pip_basic/requirements-test.txt
new file mode 100644
index 000000000..abe3e9819
--- /dev/null
+++ b/spec/fixtures/pip_basic/requirements-test.txt
@@ -0,0 +1,2 @@
+# This shouldn't be installed, since requirements-test.txt should only be used on Heroku CI.
+pytest
diff --git a/spec/fixtures/pip_basic/requirements.txt b/spec/fixtures/pip_basic/requirements.txt
new file mode 120000
index 000000000..eb513c3cd
--- /dev/null
+++ b/spec/fixtures/pip_basic/requirements.txt
@@ -0,0 +1 @@
+requirements/prod.txt
\ No newline at end of file
diff --git a/spec/fixtures/pip_basic/requirements/prod.txt b/spec/fixtures/pip_basic/requirements/prod.txt
new file mode 100644
index 000000000..728919fa5
--- /dev/null
+++ b/spec/fixtures/pip_basic/requirements/prod.txt
@@ -0,0 +1,5 @@
+# This requirements file is symlinked from the repo root's requirements.txt
+# in order to test that symlinked requirements files work.
+
+# This package has been picked since it has no dependencies and is small/fast to install.
+typing-extensions==4.15.0
diff --git a/spec/fixtures/pip_basic/setup.py b/spec/fixtures/pip_basic/setup.py
new file mode 100644
index 000000000..ab45d8b72
--- /dev/null
+++ b/spec/fixtures/pip_basic/setup.py
@@ -0,0 +1 @@
+# This file tests that the setup.py sunset error is not shown when other package manager files exist.
diff --git a/spec/fixtures/pip_compiled/requirements.txt b/spec/fixtures/pip_compiled/requirements.txt
new file mode 100644
index 000000000..ce7cf1ab7
--- /dev/null
+++ b/spec/fixtures/pip_compiled/requirements.txt
@@ -0,0 +1,2 @@
+# A quick to install package that relies on the Python headers from the base image.
+git+https://github.com/pypa/wheel.git@0.44.0#egg=extension.dist&subdirectory=tests/testdata/extension.dist
diff --git a/spec/fixtures/pip_editable/.python-version b/spec/fixtures/pip_editable/.python-version
new file mode 100644
index 000000000..6324d401a
--- /dev/null
+++ b/spec/fixtures/pip_editable/.python-version
@@ -0,0 +1 @@
+3.14
diff --git a/spec/fixtures/requirements_editable/bin/compile b/spec/fixtures/pip_editable/bin/compile
similarity index 89%
rename from spec/fixtures/requirements_editable/bin/compile
rename to spec/fixtures/pip_editable/bin/compile
index c506ad6b7..df17e9401 100755
--- a/spec/fixtures/requirements_editable/bin/compile
+++ b/spec/fixtures/pip_editable/bin/compile
@@ -9,4 +9,4 @@ BUILD_DIR="${1}"
 
 cd "${BUILD_DIR}"
 
-exec bin/test-entrypoints
+exec bin/test-entrypoints.sh
diff --git a/spec/fixtures/pip_editable/bin/detect b/spec/fixtures/pip_editable/bin/detect
new file mode 100755
index 000000000..68cdcc4a2
--- /dev/null
+++ b/spec/fixtures/pip_editable/bin/detect
@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack.
+
+set -euo pipefail
+
+echo "Inline"
diff --git a/spec/fixtures/requirements_editable/bin/post_compile b/spec/fixtures/pip_editable/bin/post_compile
similarity index 57%
rename from spec/fixtures/requirements_editable/bin/post_compile
rename to spec/fixtures/pip_editable/bin/post_compile
index 460dc2de7..6e77d159a 100755
--- a/spec/fixtures/requirements_editable/bin/post_compile
+++ b/spec/fixtures/pip_editable/bin/post_compile
@@ -2,4 +2,4 @@
 
 set -euo pipefail
 
-exec bin/test-entrypoints
+exec bin/test-entrypoints.sh
diff --git a/spec/fixtures/requirements_editable/bin/test-entrypoints b/spec/fixtures/pip_editable/bin/test-entrypoints.sh
similarity index 66%
rename from spec/fixtures/requirements_editable/bin/test-entrypoints
rename to spec/fixtures/pip_editable/bin/test-entrypoints.sh
index 4c27ba0f4..0e66f44bb 100755
--- a/spec/fixtures/requirements_editable/bin/test-entrypoints
+++ b/spec/fixtures/pip_editable/bin/test-entrypoints.sh
@@ -4,8 +4,8 @@ set -euo pipefail
 
 cd .heroku/python/lib/python*/site-packages/
 
-# List any path like strings in .egg-link, .pth, and finder files in site-packages.
-grep --extended-regexp --only-matching -- '/\S+' *.egg-link *.pth __editable___*_finder.py | sort
+# List any path like strings in the .pth and finder files in site-packages.
+grep --extended-regexp --only-matching -- '/\S+' *.pth __editable___*_finder.py | sort
 echo
 
 echo -n "Running entrypoint for the pyproject.toml-based local package: "
diff --git a/spec/fixtures/pip_editable/packages/local_package_pyproject_toml/local_package_pyproject_toml/__init__.py b/spec/fixtures/pip_editable/packages/local_package_pyproject_toml/local_package_pyproject_toml/__init__.py
new file mode 100644
index 000000000..6ce02c341
--- /dev/null
+++ b/spec/fixtures/pip_editable/packages/local_package_pyproject_toml/local_package_pyproject_toml/__init__.py
@@ -0,0 +1,2 @@
+def hello():
+    print("Hello from pyproject.toml!")
diff --git a/spec/fixtures/requirements_editable/packages/local_package_pyproject_toml/pyproject.toml b/spec/fixtures/pip_editable/packages/local_package_pyproject_toml/pyproject.toml
similarity index 100%
rename from spec/fixtures/requirements_editable/packages/local_package_pyproject_toml/pyproject.toml
rename to spec/fixtures/pip_editable/packages/local_package_pyproject_toml/pyproject.toml
diff --git a/spec/fixtures/pip_editable/packages/local_package_setup_py/local_package_setup_py/__init__.py b/spec/fixtures/pip_editable/packages/local_package_setup_py/local_package_setup_py/__init__.py
new file mode 100644
index 000000000..8dccb8a0c
--- /dev/null
+++ b/spec/fixtures/pip_editable/packages/local_package_setup_py/local_package_setup_py/__init__.py
@@ -0,0 +1,2 @@
+def hello():
+    print("Hello from setup.py!")
diff --git a/spec/fixtures/requirements_editable/packages/local_package_setup_py/setup.cfg b/spec/fixtures/pip_editable/packages/local_package_setup_py/setup.cfg
similarity index 100%
rename from spec/fixtures/requirements_editable/packages/local_package_setup_py/setup.cfg
rename to spec/fixtures/pip_editable/packages/local_package_setup_py/setup.cfg
diff --git a/spec/fixtures/requirements_editable/packages/local_package_setup_py/setup.py b/spec/fixtures/pip_editable/packages/local_package_setup_py/setup.py
similarity index 100%
rename from spec/fixtures/requirements_editable/packages/local_package_setup_py/setup.py
rename to spec/fixtures/pip_editable/packages/local_package_setup_py/setup.py
diff --git a/spec/fixtures/requirements_editable/requirements.txt b/spec/fixtures/pip_editable/requirements.txt
similarity index 66%
rename from spec/fixtures/requirements_editable/requirements.txt
rename to spec/fixtures/pip_editable/requirements.txt
index 54de167d1..a514dabc1 100644
--- a/spec/fixtures/requirements_editable/requirements.txt
+++ b/spec/fixtures/pip_editable/requirements.txt
@@ -2,4 +2,4 @@
 # https://github.com/pypa/setuptools/issues/3535
 -e ./packages/local_package_pyproject_toml
 -e ./packages/local_package_setup_py
--e git+https://github.com/benoitc/gunicorn@20.1.0#egg=gunicorn
+-e git+https://github.com/benoitc/gunicorn@56b5ad87f8d72a674145c273ed8f547513c2b409#egg=gunicorn
diff --git a/spec/fixtures/requirements_gdal/requirements.txt b/spec/fixtures/pip_gdal/requirements.txt
similarity index 100%
rename from spec/fixtures/requirements_gdal/requirements.txt
rename to spec/fixtures/pip_gdal/requirements.txt
diff --git a/spec/fixtures/pip_invalid_requirement/requirements.txt b/spec/fixtures/pip_invalid_requirement/requirements.txt
new file mode 100644
index 000000000..db42b7ee6
--- /dev/null
+++ b/spec/fixtures/pip_invalid_requirement/requirements.txt
@@ -0,0 +1 @@
+an-invalid-requirement!
diff --git a/spec/fixtures/pip_legacy_celery/requirements.txt b/spec/fixtures/pip_legacy_celery/requirements.txt
new file mode 100644
index 000000000..2abca0701
--- /dev/null
+++ b/spec/fixtures/pip_legacy_celery/requirements.txt
@@ -0,0 +1 @@
+celery==5.2.0
diff --git a/spec/fixtures/pip_oldest_python/requirements.txt b/spec/fixtures/pip_oldest_python/requirements.txt
new file mode 100644
index 000000000..f6e499a84
--- /dev/null
+++ b/spec/fixtures/pip_oldest_python/requirements.txt
@@ -0,0 +1,2 @@
+# This package has been picked since it has no dependencies and is small/fast to install.
+typing-extensions==4.15.0
diff --git a/spec/fixtures/pip_oldest_python/runtime.txt b/spec/fixtures/pip_oldest_python/runtime.txt
new file mode 100644
index 000000000..fadb07024
--- /dev/null
+++ b/spec/fixtures/pip_oldest_python/runtime.txt
@@ -0,0 +1 @@
+python-3.10.0
diff --git a/spec/fixtures/pip_pysqlite3/requirements.txt b/spec/fixtures/pip_pysqlite3/requirements.txt
new file mode 100644
index 000000000..043c5fdbe
--- /dev/null
+++ b/spec/fixtures/pip_pysqlite3/requirements.txt
@@ -0,0 +1,3 @@
+# We have to use an older version to test the custom SQLite headers error message,
+# since pysqlite3 0.6.0+ ships with precompiled wheels and so doesn't error.
+pysqlite3==0.5.4
diff --git a/spec/fixtures/pipenv_and_requirements_txt/requirements.txt b/spec/fixtures/pipenv_and_requirements_txt/requirements.txt
deleted file mode 100644
index a42590beb..000000000
--- a/spec/fixtures/pipenv_and_requirements_txt/requirements.txt
+++ /dev/null
@@ -1 +0,0 @@
-urllib3
diff --git a/spec/fixtures/pipenv_and_runtime_txt/Pipfile b/spec/fixtures/pipenv_and_runtime_txt/Pipfile
deleted file mode 100644
index 1d28b2380..000000000
--- a/spec/fixtures/pipenv_and_runtime_txt/Pipfile
+++ /dev/null
@@ -1,12 +0,0 @@
-[[source]]
-url = "https://pypi.org/simple"
-verify_ssl = true
-name = "pypi"
-
-[packages]
-urllib3 = "*"
-
-[dev-packages]
-
-[requires]
-python_version = "3.11"
diff --git a/spec/fixtures/pipenv_and_runtime_txt/Pipfile.lock b/spec/fixtures/pipenv_and_runtime_txt/Pipfile.lock
deleted file mode 100644
index 5b0ccff7d..000000000
--- a/spec/fixtures/pipenv_and_runtime_txt/Pipfile.lock
+++ /dev/null
@@ -1,30 +0,0 @@
-{
-    "_meta": {
-        "hash": {
-            "sha256": "c23e4774efa7153ba8addfbe118e9cc0c526a063275824cf25cb2198e0ff1b33"
-        },
-        "pipfile-spec": 6,
-        "requires": {
-            "python_version": "3.11"
-        },
-        "sources": [
-            {
-                "name": "pypi",
-                "url": "https://pypi.org/simple",
-                "verify_ssl": true
-            }
-        ]
-    },
-    "default": {
-        "urllib3": {
-            "hashes": [
-                "sha256:450b20ec296a467077128bff42b73080516e71b56ff59a60a02bef2232c4fa9d",
-                "sha256:d0570876c61ab9e520d776c38acbbb5b05a776d3f9ff98a5c8fd5162a444cf19"
-            ],
-            "index": "pypi",
-            "markers": "python_version >= '3.8'",
-            "version": "==2.2.1"
-        }
-    },
-    "develop": {}
-}
diff --git a/spec/fixtures/pipenv_and_runtime_txt/runtime.txt b/spec/fixtures/pipenv_and_runtime_txt/runtime.txt
deleted file mode 100644
index 74d315a82..000000000
--- a/spec/fixtures/pipenv_and_runtime_txt/runtime.txt
+++ /dev/null
@@ -1 +0,0 @@
-python-3.12.4
diff --git a/spec/fixtures/pipenv_basic/Pipfile b/spec/fixtures/pipenv_basic/Pipfile
new file mode 100644
index 000000000..ec52c677c
--- /dev/null
+++ b/spec/fixtures/pipenv_basic/Pipfile
@@ -0,0 +1,16 @@
+[[source]]
+url = "https://pypi.org/simple"
+verify_ssl = true
+name = "pypi"
+
+[packages]
+typing-extensions = "*"
+# Test that dependencies that happen to also be vendored dependencies of Pipenv are correctly installed,
+# since Pipenv's --system mode is buggy and requires a workaround to ensure they aren't skipped.
+certifi = "*"
+packaging = "*"
+
+[dev-packages]
+
+[requires]
+python_version = "3.14"
diff --git a/spec/fixtures/pipenv_basic/Pipfile.lock b/spec/fixtures/pipenv_basic/Pipfile.lock
new file mode 100644
index 000000000..059ed0e08
--- /dev/null
+++ b/spec/fixtures/pipenv_basic/Pipfile.lock
@@ -0,0 +1,48 @@
+{
+    "_meta": {
+        "hash": {
+            "sha256": "0ef98f1284f466d096b821c028367648e5141cc11150e42daa0b60172cbe5f43"
+        },
+        "pipfile-spec": 6,
+        "requires": {
+            "python_version": "3.14"
+        },
+        "sources": [
+            {
+                "name": "pypi",
+                "url": "https://pypi.org/simple",
+                "verify_ssl": true
+            }
+        ]
+    },
+    "default": {
+        "certifi": {
+            "hashes": [
+                "sha256:9943707519e4add1115f44c2bc244f782c0249876bf51b6599fee1ffbedd685c",
+                "sha256:ac726dd470482006e014ad384921ed6438c457018f4b3d204aea4281258b2120"
+            ],
+            "index": "pypi",
+            "markers": "python_version >= '3.7'",
+            "version": "==2026.1.4"
+        },
+        "packaging": {
+            "hashes": [
+                "sha256:29572ef2b1f17581046b3a2227d5c611fb25ec70ca1ba8554b24b0e69331a484",
+                "sha256:d443872c98d677bf60f6a1f2f8c1cb748e8fe762d2bf9d3148b5599295b0fc4f"
+            ],
+            "index": "pypi",
+            "markers": "python_version >= '3.8'",
+            "version": "==25.0"
+        },
+        "typing-extensions": {
+            "hashes": [
+                "sha256:0cea48d173cc12fa28ecabc3b837ea3cf6f38c6d1136f85cbaaf598984861466",
+                "sha256:f0fa19c6845758ab08074a0cfa8b7aecb71c999ca73d62883bc25cc018c4e548"
+            ],
+            "index": "pypi",
+            "markers": "python_version >= '3.9'",
+            "version": "==4.15.0"
+        }
+    },
+    "develop": {}
+}
diff --git a/spec/fixtures/pipenv_basic/bin/compile b/spec/fixtures/pipenv_basic/bin/compile
new file mode 100755
index 000000000..31c5a74fb
--- /dev/null
+++ b/spec/fixtures/pipenv_basic/bin/compile
@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack, and tests that the environment is
+# configured as expected for buildpacks that run after the Python buildpack.
+
+set -euo pipefail
+
+BUILD_DIR="${1}"
+CACHE_DIR="${2}"
+
+cd "${BUILD_DIR}"
+
+bin/print-env-vars.sh
+echo
+
+python -c 'import pprint, sys; pprint.pp(sys.path)'
+echo
+
+pipenv --version
+# We have to resort to using pip to list installed packages, since `pipenv graph` doesn't support `--system`.
+python -m ensurepip --default-pip >/dev/null
+pip list --disable-pip-version-check --exclude pip
+echo
+
+python -c 'import typing_extensions; print(typing_extensions)'
+# Test that dependencies that happen to also be vendored dependencies of Pipenv are correctly installed,
+# since Pipenv's --system mode is buggy and requires a workaround to ensure they aren't skipped.
+python -c 'import certifi; print(certifi)'
+python -c 'import packaging; print(packaging)'
+echo
+
+jq --sort-keys '.' "${CACHE_DIR}/build-data/python.json"
diff --git a/spec/fixtures/pipenv_basic/bin/detect b/spec/fixtures/pipenv_basic/bin/detect
new file mode 100755
index 000000000..68cdcc4a2
--- /dev/null
+++ b/spec/fixtures/pipenv_basic/bin/detect
@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack.
+
+set -euo pipefail
+
+echo "Inline"
diff --git a/spec/fixtures/pipenv_basic/bin/post_compile b/spec/fixtures/pipenv_basic/bin/post_compile
new file mode 100644
index 000000000..15dc8c2f3
--- /dev/null
+++ b/spec/fixtures/pipenv_basic/bin/post_compile
@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+# This intentionally uses a relative path to test that the CWD is correct.
+exec bin/print-env-vars.sh
diff --git a/spec/fixtures/pipenv_basic/bin/print-env-vars.sh b/spec/fixtures/pipenv_basic/bin/print-env-vars.sh
new file mode 100755
index 000000000..ebc9ad735
--- /dev/null
+++ b/spec/fixtures/pipenv_basic/bin/print-env-vars.sh
@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+printenv | sort | grep -vE '^(_|BUILDPACK_LOG_FILE|DYNO|HOME|OLDPWD|PORT|PS1|PWD|REQUEST_ID|SHLVL|SOURCE_VERSION|STACK|TERM)='
diff --git a/spec/fixtures/pipenv_editable/Pipfile b/spec/fixtures/pipenv_editable/Pipfile
index fcbd9c1a0..8bb51ee30 100644
--- a/spec/fixtures/pipenv_editable/Pipfile
+++ b/spec/fixtures/pipenv_editable/Pipfile
@@ -4,6 +4,7 @@ verify_ssl = true
 name = "pypi"
 
 [packages]
+gunicorn = {git = "git+https://github.com/benoitc/gunicorn", editable = true}
 local-package-pyproject-toml = {file = "packages/local_package_pyproject_toml", editable = true}
 local-package-setup-py = {file = "packages/local_package_setup_py", editable = true}
-gunicorn = {git = "git+https://github.com/benoitc/gunicorn", ref = "20.1.0", editable = true}
+pipenv-editable = {file = ".", editable = true}
diff --git a/spec/fixtures/pipenv_editable/Pipfile.lock b/spec/fixtures/pipenv_editable/Pipfile.lock
index 9ed2169b9..1ebf46629 100644
--- a/spec/fixtures/pipenv_editable/Pipfile.lock
+++ b/spec/fixtures/pipenv_editable/Pipfile.lock
@@ -1,7 +1,7 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "5de61064f835cc6b28000b3ac1b7b5c38a40829ccc38ff46088e36bb3bd628fa"
+            "sha256": "bedd8ea507283c5458c9c2cb1fd55a6e5e69fecba7814ffc96bf25e03feaeabf"
         },
         "pipfile-spec": 6,
         "requires": {},
@@ -18,7 +18,7 @@
             "editable": true,
             "git": "git+https://github.com/benoitc/gunicorn",
             "markers": "python_version >= '3.7'",
-            "ref": "61ccfd6c38d477a908e0f376757bbb884438053a"
+            "ref": "56b5ad87f8d72a674145c273ed8f547513c2b409"
         },
         "local-package-pyproject-toml": {
             "editable": true,
@@ -28,13 +28,17 @@
             "editable": true,
             "file": "packages/local_package_setup_py"
         },
-        "setuptools": {
+        "packaging": {
             "hashes": [
-                "sha256:6c1fccdac05a97e598fb0ae3bbed5904ccb317337a51139dcd51453611bbb987",
-                "sha256:c636ac361bc47580504644275c9ad802c50415c7522212252c033bd15f301f32"
+                "sha256:29572ef2b1f17581046b3a2227d5c611fb25ec70ca1ba8554b24b0e69331a484",
+                "sha256:d443872c98d677bf60f6a1f2f8c1cb748e8fe762d2bf9d3148b5599295b0fc4f"
             ],
             "markers": "python_version >= '3.8'",
-            "version": "==69.5.1"
+            "version": "==25.0"
+        },
+        "pipenv-editable": {
+            "editable": true,
+            "file": "."
         }
     },
     "develop": {}
diff --git a/spec/fixtures/pipenv_editable/bin/compile b/spec/fixtures/pipenv_editable/bin/compile
index c506ad6b7..df17e9401 100755
--- a/spec/fixtures/pipenv_editable/bin/compile
+++ b/spec/fixtures/pipenv_editable/bin/compile
@@ -9,4 +9,4 @@ BUILD_DIR="${1}"
 
 cd "${BUILD_DIR}"
 
-exec bin/test-entrypoints
+exec bin/test-entrypoints.sh
diff --git a/spec/fixtures/pipenv_editable/bin/post_compile b/spec/fixtures/pipenv_editable/bin/post_compile
index 460dc2de7..6e77d159a 100755
--- a/spec/fixtures/pipenv_editable/bin/post_compile
+++ b/spec/fixtures/pipenv_editable/bin/post_compile
@@ -2,4 +2,4 @@
 
 set -euo pipefail
 
-exec bin/test-entrypoints
+exec bin/test-entrypoints.sh
diff --git a/spec/fixtures/pipenv_editable/bin/test-entrypoints.sh b/spec/fixtures/pipenv_editable/bin/test-entrypoints.sh
new file mode 100755
index 000000000..8057cbdcf
--- /dev/null
+++ b/spec/fixtures/pipenv_editable/bin/test-entrypoints.sh
@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+cd .heroku/python/lib/python*/site-packages/
+
+# List any path like strings in the .pth and finder files in site-packages.
+grep --extended-regexp --only-matching -- '/\S+' *.pth __editable___*_finder.py | sort
+echo
+
+echo -n "Running entrypoint for the current package: "
+pipenv-editable
+
+echo -n "Running entrypoint for the pyproject.toml-based local package: "
+local_package_pyproject_toml
+
+echo -n "Running entrypoint for the setup.py-based local package: "
+local_package_setup_py
+
+echo -n "Running entrypoint for the VCS package: "
+gunicorn --version
diff --git a/spec/fixtures/pipenv_editable/packages/local_package_pyproject_toml/local_package_pyproject_toml/__init__.py b/spec/fixtures/pipenv_editable/packages/local_package_pyproject_toml/local_package_pyproject_toml/__init__.py
index b86d791d2..6ce02c341 100644
--- a/spec/fixtures/pipenv_editable/packages/local_package_pyproject_toml/local_package_pyproject_toml/__init__.py
+++ b/spec/fixtures/pipenv_editable/packages/local_package_pyproject_toml/local_package_pyproject_toml/__init__.py
@@ -1,2 +1,2 @@
 def hello():
-    print("Hello pyproject.toml!")
+    print("Hello from pyproject.toml!")
diff --git a/spec/fixtures/pipenv_editable/packages/local_package_setup_py/local_package_setup_py/__init__.py b/spec/fixtures/pipenv_editable/packages/local_package_setup_py/local_package_setup_py/__init__.py
index e98d42373..8dccb8a0c 100644
--- a/spec/fixtures/pipenv_editable/packages/local_package_setup_py/local_package_setup_py/__init__.py
+++ b/spec/fixtures/pipenv_editable/packages/local_package_setup_py/local_package_setup_py/__init__.py
@@ -1,2 +1,2 @@
 def hello():
-    print("Hello setup.py!")
+    print("Hello from setup.py!")
diff --git a/spec/fixtures/pipenv_editable/pipenv_editable/__init__.py b/spec/fixtures/pipenv_editable/pipenv_editable/__init__.py
new file mode 100644
index 000000000..0f03b9343
--- /dev/null
+++ b/spec/fixtures/pipenv_editable/pipenv_editable/__init__.py
@@ -0,0 +1,2 @@
+def main() -> None:
+    print("Hello from pipenv-editable!")
diff --git a/spec/fixtures/pipenv_editable/pyproject.toml b/spec/fixtures/pipenv_editable/pyproject.toml
new file mode 100644
index 000000000..934632a78
--- /dev/null
+++ b/spec/fixtures/pipenv_editable/pyproject.toml
@@ -0,0 +1,11 @@
+[project]
+name = "pipenv-editable"
+version = "0.0.0"
+requires-python = ">=3.14"
+
+[project.scripts]
+pipenv-editable = "pipenv_editable:main"
+
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"
diff --git a/spec/fixtures/pipenv_and_requirements_txt/Pipfile b/spec/fixtures/pipenv_lockfile_invalid_json/Pipfile
similarity index 100%
rename from spec/fixtures/pipenv_and_requirements_txt/Pipfile
rename to spec/fixtures/pipenv_lockfile_invalid_json/Pipfile
diff --git a/spec/fixtures/pipenv_lockfile_invalid_json/Pipfile.lock b/spec/fixtures/pipenv_lockfile_invalid_json/Pipfile.lock
new file mode 100644
index 000000000..0e5491864
--- /dev/null
+++ b/spec/fixtures/pipenv_lockfile_invalid_json/Pipfile.lock
@@ -0,0 +1 @@
+INVALID JSON
diff --git a/spec/fixtures/pipenv_lockfile_out_of_sync/.python-version b/spec/fixtures/pipenv_lockfile_out_of_sync/.python-version
new file mode 100644
index 000000000..6324d401a
--- /dev/null
+++ b/spec/fixtures/pipenv_lockfile_out_of_sync/.python-version
@@ -0,0 +1 @@
+3.14
diff --git a/spec/fixtures/pipenv_lockfile_out_of_sync/Pipfile b/spec/fixtures/pipenv_lockfile_out_of_sync/Pipfile
index 9bf60112c..c8c201a39 100644
--- a/spec/fixtures/pipenv_lockfile_out_of_sync/Pipfile
+++ b/spec/fixtures/pipenv_lockfile_out_of_sync/Pipfile
@@ -4,9 +4,7 @@ verify_ssl = true
 name = "pypi"
 
 [packages]
+# This dependency isn't in the lockfile.
 urllib3 = "*"
 
 [dev-packages]
-
-[requires]
-python_version = "3.12"
diff --git a/spec/fixtures/pipenv_lockfile_out_of_sync/Pipfile.lock b/spec/fixtures/pipenv_lockfile_out_of_sync/Pipfile.lock
index 4c426c2ae..d2c2cba4c 100644
--- a/spec/fixtures/pipenv_lockfile_out_of_sync/Pipfile.lock
+++ b/spec/fixtures/pipenv_lockfile_out_of_sync/Pipfile.lock
@@ -1,7 +1,7 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "a95c318e4395270fbd1e0f52dd8f12185db4c3258d4e03dd80de54b7c7aad8b1"
+            "sha256": "ebffa69a1fa192d1cef7cb42ad79231ca976565c5ce371a70160b3048d3cbc06"
         },
         "pipfile-spec": 6,
         "requires": {},
@@ -13,16 +13,6 @@
             }
         ]
     },
-    "default": {
-        "urllib3": {
-            "hashes": [
-                "sha256:450b20ec296a467077128bff42b73080516e71b56ff59a60a02bef2232c4fa9d",
-                "sha256:d0570876c61ab9e520d776c38acbbb5b05a776d3f9ff98a5c8fd5162a444cf19"
-            ],
-            "index": "pypi",
-            "markers": "python_version >= '3.8'",
-            "version": "==2.2.1"
-        }
-    },
+    "default": {},
     "develop": {}
 }
diff --git a/spec/fixtures/pipenv_mismatched_python_version/.python-version b/spec/fixtures/pipenv_mismatched_python_version/.python-version
new file mode 100644
index 000000000..d0c1d45b8
--- /dev/null
+++ b/spec/fixtures/pipenv_mismatched_python_version/.python-version
@@ -0,0 +1,2 @@
+# The version here intentionally doesn't match `python_version` in Pipfile.lock
+3.13
diff --git a/spec/fixtures/pipenv_python_3.12/Pipfile b/spec/fixtures/pipenv_mismatched_python_version/Pipfile
similarity index 80%
rename from spec/fixtures/pipenv_python_3.12/Pipfile
rename to spec/fixtures/pipenv_mismatched_python_version/Pipfile
index 9bf60112c..f438ee65c 100644
--- a/spec/fixtures/pipenv_python_3.12/Pipfile
+++ b/spec/fixtures/pipenv_mismatched_python_version/Pipfile
@@ -4,9 +4,7 @@ verify_ssl = true
 name = "pypi"
 
 [packages]
-urllib3 = "*"
-
-[dev-packages]
+typing-extensions = "*"
 
 [requires]
 python_version = "3.12"
diff --git a/spec/fixtures/pipenv_and_requirements_txt/Pipfile.lock b/spec/fixtures/pipenv_mismatched_python_version/Pipfile.lock
similarity index 53%
rename from spec/fixtures/pipenv_and_requirements_txt/Pipfile.lock
rename to spec/fixtures/pipenv_mismatched_python_version/Pipfile.lock
index cc5ce05bc..517924633 100644
--- a/spec/fixtures/pipenv_and_requirements_txt/Pipfile.lock
+++ b/spec/fixtures/pipenv_mismatched_python_version/Pipfile.lock
@@ -1,7 +1,7 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "13de6076b4dc8bbad334b7e4ae8e8ae63f7f8b4aad794c7f0173871b6927c8d0"
+            "sha256": "9661ed313a79ccb68c7dc4e639068f86ddd91e307ec2ed60498858d002e9b547"
         },
         "pipfile-spec": 6,
         "requires": {
@@ -16,14 +16,14 @@
         ]
     },
     "default": {
-        "urllib3": {
+        "typing-extensions": {
             "hashes": [
-                "sha256:450b20ec296a467077128bff42b73080516e71b56ff59a60a02bef2232c4fa9d",
-                "sha256:d0570876c61ab9e520d776c38acbbb5b05a776d3f9ff98a5c8fd5162a444cf19"
+                "sha256:0cea48d173cc12fa28ecabc3b837ea3cf6f38c6d1136f85cbaaf598984861466",
+                "sha256:f0fa19c6845758ab08074a0cfa8b7aecb71c999ca73d62883bc25cc018c4e548"
             ],
             "index": "pypi",
-            "markers": "python_version >= '3.8'",
-            "version": "==2.2.1"
+            "markers": "python_version >= '3.9'",
+            "version": "==4.15.0"
         }
     },
     "develop": {}
diff --git a/spec/fixtures/pipenv_no_lockfile/Pipfile b/spec/fixtures/pipenv_no_lockfile/Pipfile
index 67803f45b..a62d277f4 100644
--- a/spec/fixtures/pipenv_no_lockfile/Pipfile
+++ b/spec/fixtures/pipenv_no_lockfile/Pipfile
@@ -4,6 +4,9 @@ verify_ssl = true
 name = "pypi"
 
 [packages]
-urllib3 = "*"
+typing-extensions = "*"
 
 [dev-packages]
+
+[requires]
+python_version = "3.14"
diff --git a/spec/fixtures/pipenv_python_3.10/Pipfile.lock b/spec/fixtures/pipenv_python_3.10/Pipfile.lock
deleted file mode 100644
index 7b07be0dc..000000000
--- a/spec/fixtures/pipenv_python_3.10/Pipfile.lock
+++ /dev/null
@@ -1,30 +0,0 @@
-{
-    "_meta": {
-        "hash": {
-            "sha256": "0975b9caa75f76ce36c7cf6ee6fc4b63510c0970ff8e322e0b5e6ee7af2d32e8"
-        },
-        "pipfile-spec": 6,
-        "requires": {
-            "python_version": "3.10"
-        },
-        "sources": [
-            {
-                "name": "pypi",
-                "url": "https://pypi.org/simple",
-                "verify_ssl": true
-            }
-        ]
-    },
-    "default": {
-        "urllib3": {
-            "hashes": [
-                "sha256:450b20ec296a467077128bff42b73080516e71b56ff59a60a02bef2232c4fa9d",
-                "sha256:d0570876c61ab9e520d776c38acbbb5b05a776d3f9ff98a5c8fd5162a444cf19"
-            ],
-            "index": "pypi",
-            "markers": "python_version >= '3.8'",
-            "version": "==2.2.1"
-        }
-    },
-    "develop": {}
-}
diff --git a/spec/fixtures/pipenv_python_3.11/Pipfile b/spec/fixtures/pipenv_python_3.11/Pipfile
deleted file mode 100644
index 1d28b2380..000000000
--- a/spec/fixtures/pipenv_python_3.11/Pipfile
+++ /dev/null
@@ -1,12 +0,0 @@
-[[source]]
-url = "https://pypi.org/simple"
-verify_ssl = true
-name = "pypi"
-
-[packages]
-urllib3 = "*"
-
-[dev-packages]
-
-[requires]
-python_version = "3.11"
diff --git a/spec/fixtures/pipenv_python_3.11/Pipfile.lock b/spec/fixtures/pipenv_python_3.11/Pipfile.lock
deleted file mode 100644
index 5b0ccff7d..000000000
--- a/spec/fixtures/pipenv_python_3.11/Pipfile.lock
+++ /dev/null
@@ -1,30 +0,0 @@
-{
-    "_meta": {
-        "hash": {
-            "sha256": "c23e4774efa7153ba8addfbe118e9cc0c526a063275824cf25cb2198e0ff1b33"
-        },
-        "pipfile-spec": 6,
-        "requires": {
-            "python_version": "3.11"
-        },
-        "sources": [
-            {
-                "name": "pypi",
-                "url": "https://pypi.org/simple",
-                "verify_ssl": true
-            }
-        ]
-    },
-    "default": {
-        "urllib3": {
-            "hashes": [
-                "sha256:450b20ec296a467077128bff42b73080516e71b56ff59a60a02bef2232c4fa9d",
-                "sha256:d0570876c61ab9e520d776c38acbbb5b05a776d3f9ff98a5c8fd5162a444cf19"
-            ],
-            "index": "pypi",
-            "markers": "python_version >= '3.8'",
-            "version": "==2.2.1"
-        }
-    },
-    "develop": {}
-}
diff --git a/spec/fixtures/pipenv_python_3.12/Pipfile.lock b/spec/fixtures/pipenv_python_3.12/Pipfile.lock
deleted file mode 100644
index cc5ce05bc..000000000
--- a/spec/fixtures/pipenv_python_3.12/Pipfile.lock
+++ /dev/null
@@ -1,30 +0,0 @@
-{
-    "_meta": {
-        "hash": {
-            "sha256": "13de6076b4dc8bbad334b7e4ae8e8ae63f7f8b4aad794c7f0173871b6927c8d0"
-        },
-        "pipfile-spec": 6,
-        "requires": {
-            "python_version": "3.12"
-        },
-        "sources": [
-            {
-                "name": "pypi",
-                "url": "https://pypi.org/simple",
-                "verify_ssl": true
-            }
-        ]
-    },
-    "default": {
-        "urllib3": {
-            "hashes": [
-                "sha256:450b20ec296a467077128bff42b73080516e71b56ff59a60a02bef2232c4fa9d",
-                "sha256:d0570876c61ab9e520d776c38acbbb5b05a776d3f9ff98a5c8fd5162a444cf19"
-            ],
-            "index": "pypi",
-            "markers": "python_version >= '3.8'",
-            "version": "==2.2.1"
-        }
-    },
-    "develop": {}
-}
diff --git a/spec/fixtures/pipenv_python_3.6/Pipfile.lock b/spec/fixtures/pipenv_python_3.6/Pipfile.lock
deleted file mode 100644
index 738941ddd..000000000
--- a/spec/fixtures/pipenv_python_3.6/Pipfile.lock
+++ /dev/null
@@ -1,29 +0,0 @@
-{
-    "_meta": {
-        "hash": {
-            "sha256": "fe045e48581ffc6cb50af922ec04120b504f96ff6d6917fc535c8a9b76b8b71b"
-        },
-        "pipfile-spec": 6,
-        "requires": {
-            "python_version": "3.6"
-        },
-        "sources": [
-            {
-                "name": "pypi",
-                "url": "https://pypi.org/simple",
-                "verify_ssl": true
-            }
-        ]
-    },
-    "default": {
-        "urllib3": {
-            "hashes": [
-                "sha256:076907bf8fd355cde77728471316625a4d2f7e713c125f51953bb5b3eecf4f72",
-                "sha256:75edcdc2f7d85b137124a6c3c9fc3933cdeaa12ecb9a6a959f22797a0feca7e1"
-            ],
-            "index": "pypi",
-            "version": "==1.26.14"
-        }
-    },
-    "develop": {}
-}
diff --git a/spec/fixtures/pipenv_python_3.7/Pipfile b/spec/fixtures/pipenv_python_3.7/Pipfile
deleted file mode 100644
index c973bafe3..000000000
--- a/spec/fixtures/pipenv_python_3.7/Pipfile
+++ /dev/null
@@ -1,12 +0,0 @@
-[[source]]
-url = "https://pypi.org/simple"
-verify_ssl = true
-name = "pypi"
-
-[packages]
-urllib3 = "*"
-
-[dev-packages]
-
-[requires]
-python_version = "3.7"
diff --git a/spec/fixtures/pipenv_python_3.7/Pipfile.lock b/spec/fixtures/pipenv_python_3.7/Pipfile.lock
deleted file mode 100644
index 90c8735f4..000000000
--- a/spec/fixtures/pipenv_python_3.7/Pipfile.lock
+++ /dev/null
@@ -1,30 +0,0 @@
-{
-    "_meta": {
-        "hash": {
-            "sha256": "b4a533c276cc9b89b506de9007fbe2210b33f8322ea81f62989117e5ec3adc54"
-        },
-        "pipfile-spec": 6,
-        "requires": {
-            "python_version": "3.7"
-        },
-        "sources": [
-            {
-                "name": "pypi",
-                "url": "https://pypi.org/simple",
-                "verify_ssl": true
-            }
-        ]
-    },
-    "default": {
-        "urllib3": {
-            "hashes": [
-                "sha256:13abf37382ea2ce6fb744d4dad67838eec857c9f4f57009891805e0b5e123594",
-                "sha256:ef16afa8ba34a1f989db38e1dbbe0c302e4289a47856990d0682e374563ce35e"
-            ],
-            "index": "pypi",
-            "markers": "python_version >= '3.7'",
-            "version": "==2.0.5"
-        }
-    },
-    "develop": {}
-}
diff --git a/spec/fixtures/pipenv_python_3.9/Pipfile b/spec/fixtures/pipenv_python_3.9/Pipfile
deleted file mode 100644
index 7e9cf996d..000000000
--- a/spec/fixtures/pipenv_python_3.9/Pipfile
+++ /dev/null
@@ -1,12 +0,0 @@
-[[source]]
-url = "https://pypi.org/simple"
-verify_ssl = true
-name = "pypi"
-
-[packages]
-urllib3 = "*"
-
-[dev-packages]
-
-[requires]
-python_version = "3.9"
diff --git a/spec/fixtures/pipenv_python_3.9/Pipfile.lock b/spec/fixtures/pipenv_python_3.9/Pipfile.lock
deleted file mode 100644
index 527944fb6..000000000
--- a/spec/fixtures/pipenv_python_3.9/Pipfile.lock
+++ /dev/null
@@ -1,30 +0,0 @@
-{
-    "_meta": {
-        "hash": {
-            "sha256": "7776f372e3411c742b3e8a4209e67f0832f9e249d4c86ce28ece146afaef68d1"
-        },
-        "pipfile-spec": 6,
-        "requires": {
-            "python_version": "3.9"
-        },
-        "sources": [
-            {
-                "name": "pypi",
-                "url": "https://pypi.org/simple",
-                "verify_ssl": true
-            }
-        ]
-    },
-    "default": {
-        "urllib3": {
-            "hashes": [
-                "sha256:450b20ec296a467077128bff42b73080516e71b56ff59a60a02bef2232c4fa9d",
-                "sha256:d0570876c61ab9e520d776c38acbbb5b05a776d3f9ff98a5c8fd5162a444cf19"
-            ],
-            "index": "pypi",
-            "markers": "python_version >= '3.8'",
-            "version": "==2.2.1"
-        }
-    },
-    "develop": {}
-}
diff --git a/spec/fixtures/pipenv_python_full_version/Pipfile b/spec/fixtures/pipenv_python_full_version/Pipfile
index 88c5c59bc..1b3a10cc1 100644
--- a/spec/fixtures/pipenv_python_full_version/Pipfile
+++ b/spec/fixtures/pipenv_python_full_version/Pipfile
@@ -4,9 +4,13 @@ verify_ssl = true
 name = "pypi"
 
 [packages]
-urllib3 = "*"
+typing-extensions = "*"
 
 [dev-packages]
 
 [requires]
-python_full_version = "3.12.2"
+# Uses the oldest Python version supported by all stacks, to validate Pipenv works with it.
+python_full_version = "3.10.0"
+
+# `python_full_version` should take precedence over this.
+python_version = "3.12"
diff --git a/spec/fixtures/pipenv_python_full_version/Pipfile.lock b/spec/fixtures/pipenv_python_full_version/Pipfile.lock
index 2346c8a33..8b1a4f32a 100644
--- a/spec/fixtures/pipenv_python_full_version/Pipfile.lock
+++ b/spec/fixtures/pipenv_python_full_version/Pipfile.lock
@@ -1,11 +1,12 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "5f4af5700c245f61e22d09479627ca936d458a6aa693452337170f369c642f40"
+            "sha256": "e9ceff57b2002f3a53ac8e84fc449e7aacbb62139f45e8299bde332e3ef9f6b2"
         },
         "pipfile-spec": 6,
         "requires": {
-            "python_full_version": "3.12.2"
+            "python_full_version": "3.10.0",
+            "python_version": "3.12"
         },
         "sources": [
             {
@@ -16,14 +17,14 @@
         ]
     },
     "default": {
-        "urllib3": {
+        "typing-extensions": {
             "hashes": [
-                "sha256:450b20ec296a467077128bff42b73080516e71b56ff59a60a02bef2232c4fa9d",
-                "sha256:d0570876c61ab9e520d776c38acbbb5b05a776d3f9ff98a5c8fd5162a444cf19"
+                "sha256:0cea48d173cc12fa28ecabc3b837ea3cf6f38c6d1136f85cbaaf598984861466",
+                "sha256:f0fa19c6845758ab08074a0cfa8b7aecb71c999ca73d62883bc25cc018c4e548"
             ],
             "index": "pypi",
-            "markers": "python_version >= '3.8'",
-            "version": "==2.2.1"
+            "markers": "python_version >= '3.9'",
+            "version": "==4.15.0"
         }
     },
     "develop": {}
diff --git a/spec/fixtures/pipenv_python_full_version_invalid/Pipfile b/spec/fixtures/pipenv_python_full_version_invalid/Pipfile
index 683918cbd..4016fd876 100644
--- a/spec/fixtures/pipenv_python_full_version_invalid/Pipfile
+++ b/spec/fixtures/pipenv_python_full_version_invalid/Pipfile
@@ -4,9 +4,9 @@ verify_ssl = true
 name = "pypi"
 
 [packages]
-urllib3 = "*"
+typing-extensions = "*"
 
 [dev-packages]
 
 [requires]
-python_full_version = "X.Y.Z"
+python_full_version = "3.9.*"
diff --git a/spec/fixtures/pipenv_python_full_version_invalid/Pipfile.lock b/spec/fixtures/pipenv_python_full_version_invalid/Pipfile.lock
index 3b2d178ab..983c376a9 100644
--- a/spec/fixtures/pipenv_python_full_version_invalid/Pipfile.lock
+++ b/spec/fixtures/pipenv_python_full_version_invalid/Pipfile.lock
@@ -1,11 +1,11 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "7efd722f93856d46f698123972037594c6b8621e54b5a2be8ce71f5707a13c33"
+            "sha256": "254efba85c5858a7dfe232cb38f9ead91bf6e50bbf82f51a8a5a01904ca8712e"
         },
         "pipfile-spec": 6,
         "requires": {
-            "python_full_version": "X.Y.Z"
+            "python_full_version": "3.9.*"
         },
         "sources": [
             {
@@ -16,14 +16,14 @@
         ]
     },
     "default": {
-        "urllib3": {
+        "typing-extensions": {
             "hashes": [
-                "sha256:450b20ec296a467077128bff42b73080516e71b56ff59a60a02bef2232c4fa9d",
-                "sha256:d0570876c61ab9e520d776c38acbbb5b05a776d3f9ff98a5c8fd5162a444cf19"
+                "sha256:0cea48d173cc12fa28ecabc3b837ea3cf6f38c6d1136f85cbaaf598984861466",
+                "sha256:f0fa19c6845758ab08074a0cfa8b7aecb71c999ca73d62883bc25cc018c4e548"
             ],
             "index": "pypi",
-            "markers": "python_version >= '3.8'",
-            "version": "==2.2.1"
+            "markers": "python_version >= '3.9'",
+            "version": "==4.15.0"
         }
     },
     "develop": {}
diff --git a/spec/fixtures/pipenv_python_version_and_python_version_file/.python-version b/spec/fixtures/pipenv_python_version_and_python_version_file/.python-version
new file mode 100644
index 000000000..6d977fdcf
--- /dev/null
+++ b/spec/fixtures/pipenv_python_version_and_python_version_file/.python-version
@@ -0,0 +1,2 @@
+# This should take precedence over the Python version in Pipfile.lock.
+3.13
diff --git a/spec/fixtures/pipenv_python_3.10/Pipfile b/spec/fixtures/pipenv_python_version_and_python_version_file/Pipfile
similarity index 50%
rename from spec/fixtures/pipenv_python_3.10/Pipfile
rename to spec/fixtures/pipenv_python_version_and_python_version_file/Pipfile
index 37291dc4f..d9d1ea61b 100644
--- a/spec/fixtures/pipenv_python_3.10/Pipfile
+++ b/spec/fixtures/pipenv_python_version_and_python_version_file/Pipfile
@@ -4,9 +4,10 @@ verify_ssl = true
 name = "pypi"
 
 [packages]
-urllib3 = "*"
+typing-extensions = "*"
 
 [dev-packages]
 
 [requires]
-python_version = "3.10"
+# The version in .python-version should take precedence over this.
+python_version = "3.13"
diff --git a/spec/fixtures/pipenv_python_version_and_python_version_file/Pipfile.lock b/spec/fixtures/pipenv_python_version_and_python_version_file/Pipfile.lock
new file mode 100644
index 000000000..2a3e9cd35
--- /dev/null
+++ b/spec/fixtures/pipenv_python_version_and_python_version_file/Pipfile.lock
@@ -0,0 +1,30 @@
+{
+    "_meta": {
+        "hash": {
+            "sha256": "83d7242edaa31ec24731c102c5debc217f3e5f5fa5b4e992de07d4d25805715e"
+        },
+        "pipfile-spec": 6,
+        "requires": {
+            "python_version": "3.13"
+        },
+        "sources": [
+            {
+                "name": "pypi",
+                "url": "https://pypi.org/simple",
+                "verify_ssl": true
+            }
+        ]
+    },
+    "default": {
+        "typing-extensions": {
+            "hashes": [
+                "sha256:0cea48d173cc12fa28ecabc3b837ea3cf6f38c6d1136f85cbaaf598984861466",
+                "sha256:f0fa19c6845758ab08074a0cfa8b7aecb71c999ca73d62883bc25cc018c4e548"
+            ],
+            "index": "pypi",
+            "markers": "python_version >= '3.9'",
+            "version": "==4.15.0"
+        }
+    },
+    "develop": {}
+}
diff --git a/spec/fixtures/pipenv_python_3.8/Pipfile b/spec/fixtures/pipenv_python_version_eol/Pipfile
similarity index 85%
rename from spec/fixtures/pipenv_python_3.8/Pipfile
rename to spec/fixtures/pipenv_python_version_eol/Pipfile
index 5aea20cfa..40c03e309 100644
--- a/spec/fixtures/pipenv_python_3.8/Pipfile
+++ b/spec/fixtures/pipenv_python_version_eol/Pipfile
@@ -4,7 +4,7 @@ verify_ssl = true
 name = "pypi"
 
 [packages]
-urllib3 = "*"
+typing-extensions = "*"
 
 [dev-packages]
 
diff --git a/spec/fixtures/pipenv_python_3.8/Pipfile.lock b/spec/fixtures/pipenv_python_version_eol/Pipfile.lock
similarity index 59%
rename from spec/fixtures/pipenv_python_3.8/Pipfile.lock
rename to spec/fixtures/pipenv_python_version_eol/Pipfile.lock
index f1618e6a9..026a1b0b1 100644
--- a/spec/fixtures/pipenv_python_3.8/Pipfile.lock
+++ b/spec/fixtures/pipenv_python_version_eol/Pipfile.lock
@@ -1,7 +1,7 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "e9eb0bba6cb0a97533d25cd3d68db92d4afd6b1dc88cd7a51607d8c34475eae0"
+            "sha256": "feaf6b91bd5a191f779b2c2199b3e328369c87e6a598f02a3ba6c76d877e176f"
         },
         "pipfile-spec": 6,
         "requires": {
@@ -16,14 +16,14 @@
         ]
     },
     "default": {
-        "urllib3": {
+        "typing-extensions": {
             "hashes": [
-                "sha256:450b20ec296a467077128bff42b73080516e71b56ff59a60a02bef2232c4fa9d",
-                "sha256:d0570876c61ab9e520d776c38acbbb5b05a776d3f9ff98a5c8fd5162a444cf19"
+                "sha256:a439e7c04b49fec3e5d3e2beaa21755cadbbdc391694e28ccdd36ca4a1408f8c",
+                "sha256:e6c81219bd689f51865d9e372991c540bda33a0379d5573cddb9a3a23f7caaef"
             ],
             "index": "pypi",
             "markers": "python_version >= '3.8'",
-            "version": "==2.2.1"
+            "version": "==4.13.2"
         }
     },
     "develop": {}
diff --git a/spec/fixtures/pipenv_python_version_invalid/Pipfile b/spec/fixtures/pipenv_python_version_invalid/Pipfile
index 326889f7a..43fe5b889 100644
--- a/spec/fixtures/pipenv_python_version_invalid/Pipfile
+++ b/spec/fixtures/pipenv_python_version_invalid/Pipfile
@@ -4,7 +4,7 @@ verify_ssl = true
 name = "pypi"
 
 [packages]
-urllib3 = "*"
+typing-extensions = "*"
 
 [dev-packages]
 
diff --git a/spec/fixtures/pipenv_python_version_invalid/Pipfile.lock b/spec/fixtures/pipenv_python_version_invalid/Pipfile.lock
index 47d197cdd..44f3e9fc6 100644
--- a/spec/fixtures/pipenv_python_version_invalid/Pipfile.lock
+++ b/spec/fixtures/pipenv_python_version_invalid/Pipfile.lock
@@ -1,7 +1,7 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "584096cd3f6a5c68b5f2e21993fc104773efb507ed1945ca26c789d86b22d883"
+            "sha256": "c86b61d10a1742dfbc75378ee86a81c24420506b154b9c19d69aa6e6c02c61b2"
         },
         "pipfile-spec": 6,
         "requires": {
@@ -16,14 +16,14 @@
         ]
     },
     "default": {
-        "urllib3": {
+        "typing-extensions": {
             "hashes": [
-                "sha256:450b20ec296a467077128bff42b73080516e71b56ff59a60a02bef2232c4fa9d",
-                "sha256:d0570876c61ab9e520d776c38acbbb5b05a776d3f9ff98a5c8fd5162a444cf19"
+                "sha256:0cea48d173cc12fa28ecabc3b837ea3cf6f38c6d1136f85cbaaf598984861466",
+                "sha256:f0fa19c6845758ab08074a0cfa8b7aecb71c999ca73d62883bc25cc018c4e548"
             ],
             "index": "pypi",
-            "markers": "python_version >= '3.8'",
-            "version": "==2.2.1"
+            "markers": "python_version >= '3.9'",
+            "version": "==4.15.0"
         }
     },
     "develop": {}
diff --git a/spec/fixtures/pipenv_python_version_unspecified/Pipfile b/spec/fixtures/pipenv_python_version_unspecified/Pipfile
index 67803f45b..496fa1558 100644
--- a/spec/fixtures/pipenv_python_version_unspecified/Pipfile
+++ b/spec/fixtures/pipenv_python_version_unspecified/Pipfile
@@ -4,6 +4,6 @@ verify_ssl = true
 name = "pypi"
 
 [packages]
-urllib3 = "*"
+typing-extensions = "*"
 
 [dev-packages]
diff --git a/spec/fixtures/pipenv_python_version_unspecified/Pipfile.lock b/spec/fixtures/pipenv_python_version_unspecified/Pipfile.lock
index 4c426c2ae..2b7b232d6 100644
--- a/spec/fixtures/pipenv_python_version_unspecified/Pipfile.lock
+++ b/spec/fixtures/pipenv_python_version_unspecified/Pipfile.lock
@@ -1,7 +1,7 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "a95c318e4395270fbd1e0f52dd8f12185db4c3258d4e03dd80de54b7c7aad8b1"
+            "sha256": "beb76460a63ef2f29eec7b281a3c7114d442db105096d7472b4b72a7504df8fe"
         },
         "pipfile-spec": 6,
         "requires": {},
@@ -14,14 +14,14 @@
         ]
     },
     "default": {
-        "urllib3": {
+        "typing-extensions": {
             "hashes": [
-                "sha256:450b20ec296a467077128bff42b73080516e71b56ff59a60a02bef2232c4fa9d",
-                "sha256:d0570876c61ab9e520d776c38acbbb5b05a776d3f9ff98a5c8fd5162a444cf19"
+                "sha256:0cea48d173cc12fa28ecabc3b837ea3cf6f38c6d1136f85cbaaf598984861466",
+                "sha256:f0fa19c6845758ab08074a0cfa8b7aecb71c999ca73d62883bc25cc018c4e548"
             ],
             "index": "pypi",
-            "markers": "python_version >= '3.8'",
-            "version": "==2.2.1"
+            "markers": "python_version >= '3.9'",
+            "version": "==4.15.0"
         }
     },
     "develop": {}
diff --git a/spec/fixtures/poetry_basic/.python-version b/spec/fixtures/poetry_basic/.python-version
new file mode 100644
index 000000000..6324d401a
--- /dev/null
+++ b/spec/fixtures/poetry_basic/.python-version
@@ -0,0 +1 @@
+3.14
diff --git a/spec/fixtures/poetry_basic/bin/compile b/spec/fixtures/poetry_basic/bin/compile
new file mode 100755
index 000000000..8b23ed9ce
--- /dev/null
+++ b/spec/fixtures/poetry_basic/bin/compile
@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack, and tests that the environment is
+# configured as expected for buildpacks that run after the Python buildpack.
+
+set -euo pipefail
+
+BUILD_DIR="${1}"
+CACHE_DIR="${2}"
+
+cd "${BUILD_DIR}"
+
+bin/print-env-vars.sh
+echo
+
+python -c 'import pprint, sys; pprint.pp(sys.path)'
+echo
+
+poetry --version
+# The show command also lists dependencies that are in optional groups in pyproject.toml
+# but that aren't actually installed, for which the only option is to filter out by hand.
+poetry show | grep -v ' (!) '
+echo
+
+python -c 'import typing_extensions; print(typing_extensions)'
+echo
+
+jq --sort-keys '.' "${CACHE_DIR}/build-data/python.json"
diff --git a/spec/fixtures/poetry_basic/bin/detect b/spec/fixtures/poetry_basic/bin/detect
new file mode 100755
index 000000000..68cdcc4a2
--- /dev/null
+++ b/spec/fixtures/poetry_basic/bin/detect
@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack.
+
+set -euo pipefail
+
+echo "Inline"
diff --git a/spec/fixtures/poetry_basic/bin/post_compile b/spec/fixtures/poetry_basic/bin/post_compile
new file mode 100644
index 000000000..15dc8c2f3
--- /dev/null
+++ b/spec/fixtures/poetry_basic/bin/post_compile
@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+# This intentionally uses a relative path to test that the CWD is correct.
+exec bin/print-env-vars.sh
diff --git a/spec/fixtures/poetry_basic/bin/print-env-vars.sh b/spec/fixtures/poetry_basic/bin/print-env-vars.sh
new file mode 100755
index 000000000..ebc9ad735
--- /dev/null
+++ b/spec/fixtures/poetry_basic/bin/print-env-vars.sh
@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+printenv | sort | grep -vE '^(_|BUILDPACK_LOG_FILE|DYNO|HOME|OLDPWD|PORT|PS1|PWD|REQUEST_ID|SHLVL|SOURCE_VERSION|STACK|TERM)='
diff --git a/spec/fixtures/poetry_basic/poetry.lock b/spec/fixtures/poetry_basic/poetry.lock
new file mode 100644
index 000000000..51cc64181
--- /dev/null
+++ b/spec/fixtures/poetry_basic/poetry.lock
@@ -0,0 +1,108 @@
+# This file is automatically @generated by Poetry 2.2.1 and should not be changed by hand.
+
+[[package]]
+name = "colorama"
+version = "0.4.6"
+description = "Cross-platform colored terminal text."
+optional = false
+python-versions = "!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*,!=3.5.*,!=3.6.*,>=2.7"
+groups = ["dev"]
+markers = "sys_platform == \"win32\""
+files = [
+    {file = "colorama-0.4.6-py2.py3-none-any.whl", hash = "sha256:4f1d9991f5acc0ca119f9d443620b77f9d6b33703e51011c16baf57afb285fc6"},
+    {file = "colorama-0.4.6.tar.gz", hash = "sha256:08695f5cb7ed6e0531a20572697297273c47b8cae5a63ffc6d6ed5c201be6e44"},
+]
+
+[[package]]
+name = "iniconfig"
+version = "2.3.0"
+description = "brain-dead simple config-ini parsing"
+optional = false
+python-versions = ">=3.10"
+groups = ["dev"]
+files = [
+    {file = "iniconfig-2.3.0-py3-none-any.whl", hash = "sha256:f631c04d2c48c52b84d0d0549c99ff3859c98df65b3101406327ecc7d53fbf12"},
+    {file = "iniconfig-2.3.0.tar.gz", hash = "sha256:c76315c77db068650d49c5b56314774a7804df16fee4402c1f19d6d15d8c4730"},
+]
+
+[[package]]
+name = "packaging"
+version = "25.0"
+description = "Core utilities for Python packages"
+optional = false
+python-versions = ">=3.8"
+groups = ["dev"]
+files = [
+    {file = "packaging-25.0-py3-none-any.whl", hash = "sha256:29572ef2b1f17581046b3a2227d5c611fb25ec70ca1ba8554b24b0e69331a484"},
+    {file = "packaging-25.0.tar.gz", hash = "sha256:d443872c98d677bf60f6a1f2f8c1cb748e8fe762d2bf9d3148b5599295b0fc4f"},
+]
+
+[[package]]
+name = "pluggy"
+version = "1.6.0"
+description = "plugin and hook calling mechanisms for python"
+optional = false
+python-versions = ">=3.9"
+groups = ["dev"]
+files = [
+    {file = "pluggy-1.6.0-py3-none-any.whl", hash = "sha256:e920276dd6813095e9377c0bc5566d94c932c33b27a3e3945d8389c374dd4746"},
+    {file = "pluggy-1.6.0.tar.gz", hash = "sha256:7dcc130b76258d33b90f61b658791dede3486c3e6bfb003ee5c9bfb396dd22f3"},
+]
+
+[package.extras]
+dev = ["pre-commit", "tox"]
+testing = ["coverage", "pytest", "pytest-benchmark"]
+
+[[package]]
+name = "pygments"
+version = "2.19.2"
+description = "Pygments is a syntax highlighting package written in Python."
+optional = false
+python-versions = ">=3.8"
+groups = ["dev"]
+files = [
+    {file = "pygments-2.19.2-py3-none-any.whl", hash = "sha256:86540386c03d588bb81d44bc3928634ff26449851e99741617ecb9037ee5ec0b"},
+    {file = "pygments-2.19.2.tar.gz", hash = "sha256:636cb2477cec7f8952536970bc533bc43743542f70392ae026374600add5b887"},
+]
+
+[package.extras]
+windows-terminal = ["colorama (>=0.4.6)"]
+
+[[package]]
+name = "pytest"
+version = "9.0.1"
+description = "pytest: simple powerful testing with Python"
+optional = false
+python-versions = ">=3.10"
+groups = ["dev"]
+files = [
+    {file = "pytest-9.0.1-py3-none-any.whl", hash = "sha256:67be0030d194df2dfa7b556f2e56fb3c3315bd5c8822c6951162b92b32ce7dad"},
+    {file = "pytest-9.0.1.tar.gz", hash = "sha256:3e9c069ea73583e255c3b21cf46b8d3c56f6e3a1a8f6da94ccb0fcf57b9d73c8"},
+]
+
+[package.dependencies]
+colorama = {version = ">=0.4", markers = "sys_platform == \"win32\""}
+iniconfig = ">=1.0.1"
+packaging = ">=22"
+pluggy = ">=1.5,<2"
+pygments = ">=2.7.2"
+
+[package.extras]
+dev = ["argcomplete", "attrs (>=19.2)", "hypothesis (>=3.56)", "mock", "requests", "setuptools", "xmlschema"]
+
+[[package]]
+name = "typing-extensions"
+version = "4.15.0"
+description = "Backported and Experimental Type Hints for Python 3.9+"
+optional = false
+python-versions = ">=3.9"
+groups = ["main"]
+files = [
+    {file = "typing_extensions-4.15.0-py3-none-any.whl", hash = "sha256:f0fa19c6845758ab08074a0cfa8b7aecb71c999ca73d62883bc25cc018c4e548"},
+    {file = "typing_extensions-4.15.0.tar.gz", hash = "sha256:0cea48d173cc12fa28ecabc3b837ea3cf6f38c6d1136f85cbaaf598984861466"},
+]
+
+[metadata]
+lock-version = "2.1"
+python-versions = ">=3.14"
+content-hash = "a0f8d6facd04ce28abc860e56bb4af6e1acac71a1f2a93e4e6ed4e13a299e055"
diff --git a/spec/fixtures/poetry_basic/pyproject.toml b/spec/fixtures/poetry_basic/pyproject.toml
new file mode 100644
index 000000000..3a23e1a00
--- /dev/null
+++ b/spec/fixtures/poetry_basic/pyproject.toml
@@ -0,0 +1,16 @@
+[project]
+name = "poetry-basic"
+version = "0.0.0"
+requires-python = ">=3.14"
+dependencies = [
+    "typing-extensions",
+]
+
+[dependency-groups]
+# This group shouldn't be installed due to us passing `--only main`.
+dev = [
+    "pytest",
+]
+
+[tool.poetry]
+package-mode = false
diff --git a/spec/fixtures/poetry_editable/bin/compile b/spec/fixtures/poetry_editable/bin/compile
new file mode 100755
index 000000000..df17e9401
--- /dev/null
+++ b/spec/fixtures/poetry_editable/bin/compile
@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack, and tests that editable requirements are
+# usable by buildpacks that run after the Python buildpack during the build.
+
+set -euo pipefail
+
+BUILD_DIR="${1}"
+
+cd "${BUILD_DIR}"
+
+exec bin/test-entrypoints.sh
diff --git a/spec/fixtures/poetry_editable/bin/detect b/spec/fixtures/poetry_editable/bin/detect
new file mode 100755
index 000000000..68cdcc4a2
--- /dev/null
+++ b/spec/fixtures/poetry_editable/bin/detect
@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack.
+
+set -euo pipefail
+
+echo "Inline"
diff --git a/spec/fixtures/poetry_editable/bin/post_compile b/spec/fixtures/poetry_editable/bin/post_compile
new file mode 100755
index 000000000..6e77d159a
--- /dev/null
+++ b/spec/fixtures/poetry_editable/bin/post_compile
@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+exec bin/test-entrypoints.sh
diff --git a/spec/fixtures/poetry_editable/bin/test-entrypoints.sh b/spec/fixtures/poetry_editable/bin/test-entrypoints.sh
new file mode 100755
index 000000000..dbdf50fee
--- /dev/null
+++ b/spec/fixtures/poetry_editable/bin/test-entrypoints.sh
@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+cd .heroku/python/lib/python*/site-packages/
+
+# List any path like strings in the .pth and finder files in site-packages.
+grep --extended-regexp --only-matching -- '/\S+' *.pth __editable___*_finder.py | sort
+echo
+
+echo -n "Running entrypoint for the current package: "
+poetry-editable
+
+echo -n "Running entrypoint for the pyproject.toml-based local package: "
+local_package_pyproject_toml
+
+echo -n "Running entrypoint for the setup.py-based local package: "
+local_package_setup_py
+
+echo -n "Running entrypoint for the VCS package: "
+gunicorn --version
diff --git a/spec/fixtures/poetry_editable/packages/local_package_pyproject_toml/local_package_pyproject_toml/__init__.py b/spec/fixtures/poetry_editable/packages/local_package_pyproject_toml/local_package_pyproject_toml/__init__.py
new file mode 100644
index 000000000..6ce02c341
--- /dev/null
+++ b/spec/fixtures/poetry_editable/packages/local_package_pyproject_toml/local_package_pyproject_toml/__init__.py
@@ -0,0 +1,2 @@
+def hello():
+    print("Hello from pyproject.toml!")
diff --git a/spec/fixtures/poetry_editable/packages/local_package_pyproject_toml/pyproject.toml b/spec/fixtures/poetry_editable/packages/local_package_pyproject_toml/pyproject.toml
new file mode 100644
index 000000000..f567c3777
--- /dev/null
+++ b/spec/fixtures/poetry_editable/packages/local_package_pyproject_toml/pyproject.toml
@@ -0,0 +1,6 @@
+[project]
+name = "local_package_pyproject_toml"
+version = "0.0.1"
+
+[project.scripts]
+local_package_pyproject_toml = "local_package_pyproject_toml:hello"
diff --git a/spec/fixtures/poetry_editable/packages/local_package_setup_py/local_package_setup_py/__init__.py b/spec/fixtures/poetry_editable/packages/local_package_setup_py/local_package_setup_py/__init__.py
new file mode 100644
index 000000000..8dccb8a0c
--- /dev/null
+++ b/spec/fixtures/poetry_editable/packages/local_package_setup_py/local_package_setup_py/__init__.py
@@ -0,0 +1,2 @@
+def hello():
+    print("Hello from setup.py!")
diff --git a/spec/fixtures/poetry_editable/packages/local_package_setup_py/setup.cfg b/spec/fixtures/poetry_editable/packages/local_package_setup_py/setup.cfg
new file mode 100644
index 000000000..eff513964
--- /dev/null
+++ b/spec/fixtures/poetry_editable/packages/local_package_setup_py/setup.cfg
@@ -0,0 +1,10 @@
+[metadata]
+name = local_package_setup_py
+version = 0.0.1
+
+[options]
+packages = local_package_setup_py
+
+[options.entry_points]
+console_scripts =
+    local_package_setup_py = local_package_setup_py:hello
diff --git a/spec/fixtures/poetry_editable/packages/local_package_setup_py/setup.py b/spec/fixtures/poetry_editable/packages/local_package_setup_py/setup.py
new file mode 100644
index 000000000..606849326
--- /dev/null
+++ b/spec/fixtures/poetry_editable/packages/local_package_setup_py/setup.py
@@ -0,0 +1,3 @@
+from setuptools import setup
+
+setup()
diff --git a/spec/fixtures/poetry_editable/poetry.lock b/spec/fixtures/poetry_editable/poetry.lock
new file mode 100644
index 000000000..9e21fd4e9
--- /dev/null
+++ b/spec/fixtures/poetry_editable/poetry.lock
@@ -0,0 +1,72 @@
+# This file is automatically @generated by Poetry 2.2.1 and should not be changed by hand.
+
+[[package]]
+name = "gunicorn"
+version = "23.0.0"
+description = "WSGI HTTP Server for UNIX"
+optional = false
+python-versions = ">=3.10"
+groups = ["main"]
+files = []
+develop = true
+
+[package.dependencies]
+packaging = "*"
+
+[package.extras]
+eventlet = ["eventlet (>=0.24.1,!=0.36.0)"]
+gevent = ["gevent (>=1.4.0)"]
+setproctitle = ["setproctitle"]
+testing = ["coverage", "eventlet", "gevent", "pytest", "pytest-cov"]
+tornado = ["tornado (>=0.2)"]
+
+[package.source]
+type = "git"
+url = "https://github.com/benoitc/gunicorn.git"
+reference = "HEAD"
+resolved_reference = "56b5ad87f8d72a674145c273ed8f547513c2b409"
+
+[[package]]
+name = "local-package-pyproject-toml"
+version = "0.0.1"
+description = ""
+optional = false
+python-versions = "*"
+groups = ["main"]
+files = []
+develop = true
+
+[package.source]
+type = "directory"
+url = "packages/local_package_pyproject_toml"
+
+[[package]]
+name = "local_package_setup_py"
+version = "0.0.1"
+description = ""
+optional = false
+python-versions = "*"
+groups = ["main"]
+files = []
+develop = true
+
+[package.source]
+type = "directory"
+url = "packages/local_package_setup_py"
+
+[[package]]
+name = "packaging"
+version = "25.0"
+description = "Core utilities for Python packages"
+optional = false
+python-versions = ">=3.8"
+groups = ["main"]
+files = [
+    {file = "packaging-25.0-py3-none-any.whl", hash = "sha256:29572ef2b1f17581046b3a2227d5c611fb25ec70ca1ba8554b24b0e69331a484"},
+    {file = "packaging-25.0.tar.gz", hash = "sha256:d443872c98d677bf60f6a1f2f8c1cb748e8fe762d2bf9d3148b5599295b0fc4f"},
+]
+
+[metadata]
+lock-version = "2.1"
+python-versions = "^3.14"
+content-hash = "f0f202f553940509c2ae9bfc77fdd0df2448f9df01eee351f823249128699160"
diff --git a/spec/fixtures/poetry_editable/poetry_editable/__init__.py b/spec/fixtures/poetry_editable/poetry_editable/__init__.py
new file mode 100644
index 000000000..e00661f98
--- /dev/null
+++ b/spec/fixtures/poetry_editable/poetry_editable/__init__.py
@@ -0,0 +1,2 @@
+def main() -> None:
+    print("Hello from poetry-editable!")
diff --git a/spec/fixtures/poetry_editable/pyproject.toml b/spec/fixtures/poetry_editable/pyproject.toml
new file mode 100644
index 000000000..cc56aaad4
--- /dev/null
+++ b/spec/fixtures/poetry_editable/pyproject.toml
@@ -0,0 +1,18 @@
+[tool.poetry]
+name = "poetry-editable"
+version = "0.0.1"
+description = ""
+authors = []
+
+[tool.poetry.dependencies]
+python = "^3.14"
+gunicorn = { git = "https://github.com/benoitc/gunicorn.git", develop = true }
+local-package-pyproject-toml = { path = "packages/local_package_pyproject_toml", develop = true }
+local-package-setup-py = { path = "packages/local_package_setup_py", develop = true }
+
+[tool.poetry.scripts]
+poetry-editable = 'poetry_editable:main'
+
+[build-system]
+requires = ["poetry-core"]
+build-backend = "poetry.core.masonry.api"
diff --git a/spec/fixtures/poetry_lockfile_out_of_sync/poetry.lock b/spec/fixtures/poetry_lockfile_out_of_sync/poetry.lock
new file mode 100644
index 000000000..9b4be8159
--- /dev/null
+++ b/spec/fixtures/poetry_lockfile_out_of_sync/poetry.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Poetry 2.2.1 and should not be changed by hand.
+package = []
+
+[metadata]
+lock-version = "2.1"
+python-versions = "^3.14"
+content-hash = "d3f696e8f01aec1733802da3db722ca7c5e48e3d967cd7e2ce28ee65396abe6c"
diff --git a/spec/fixtures/poetry_lockfile_out_of_sync/pyproject.toml b/spec/fixtures/poetry_lockfile_out_of_sync/pyproject.toml
new file mode 100644
index 000000000..1c9cd7013
--- /dev/null
+++ b/spec/fixtures/poetry_lockfile_out_of_sync/pyproject.toml
@@ -0,0 +1,8 @@
+[tool.poetry]
+package-mode = false
+
+[tool.poetry.dependencies]
+python = "^3.14"
+
+# This dependency isn't in the lockfile.
+typing-extensions = "*"
diff --git a/spec/fixtures/poetry_mismatched_python_version/.python-version b/spec/fixtures/poetry_mismatched_python_version/.python-version
new file mode 100644
index 000000000..88c9ebc82
--- /dev/null
+++ b/spec/fixtures/poetry_mismatched_python_version/.python-version
@@ -0,0 +1,2 @@
+# The version here intentionally doesn't match requires-python in pyproject.toml
+3.13
diff --git a/spec/fixtures/poetry_mismatched_python_version/poetry.lock b/spec/fixtures/poetry_mismatched_python_version/poetry.lock
new file mode 100644
index 000000000..d7e662543
--- /dev/null
+++ b/spec/fixtures/poetry_mismatched_python_version/poetry.lock
@@ -0,0 +1,18 @@
+# This file is automatically @generated by Poetry 2.2.1 and should not be changed by hand.
+
+[[package]]
+name = "typing-extensions"
+version = "4.15.0"
+description = "Backported and Experimental Type Hints for Python 3.9+"
+optional = false
+python-versions = ">=3.9"
+groups = ["main"]
+files = [
+    {file = "typing_extensions-4.15.0-py3-none-any.whl", hash = "sha256:f0fa19c6845758ab08074a0cfa8b7aecb71c999ca73d62883bc25cc018c4e548"},
+    {file = "typing_extensions-4.15.0.tar.gz", hash = "sha256:0cea48d173cc12fa28ecabc3b837ea3cf6f38c6d1136f85cbaaf598984861466"},
+]
+
+[metadata]
+lock-version = "2.1"
+python-versions = "3.12.*"
+content-hash = "30427e182c131408fcdf15a6838a771f7e7c1e67fa6e0c33ccc82194052de8df"
diff --git a/spec/fixtures/poetry_mismatched_python_version/pyproject.toml b/spec/fixtures/poetry_mismatched_python_version/pyproject.toml
new file mode 100644
index 000000000..ed26e3dc4
--- /dev/null
+++ b/spec/fixtures/poetry_mismatched_python_version/pyproject.toml
@@ -0,0 +1,13 @@
+[project]
+name = "poetry-mismatched-python-version"
+version = "0.0.0"
+# This Python version intentionally doesn't match that in .python-version.
+# The version here also matches the distro Python version in Ubuntu 24.04,
+# so we can also test Poetry doesn't fall back to system Python.
+requires-python = "3.12.*"
+dependencies = [
+    "typing-extensions"
+]
+
+[tool.poetry]
+package-mode = false
diff --git a/spec/fixtures/poetry_oldest_python/.python-version b/spec/fixtures/poetry_oldest_python/.python-version
new file mode 100644
index 000000000..30291cba2
--- /dev/null
+++ b/spec/fixtures/poetry_oldest_python/.python-version
@@ -0,0 +1 @@
+3.10.0
diff --git a/spec/fixtures/poetry_oldest_python/brotli/.gitkeep b/spec/fixtures/poetry_oldest_python/brotli/.gitkeep
new file mode 100644
index 000000000..98d7394a0
--- /dev/null
+++ b/spec/fixtures/poetry_oldest_python/brotli/.gitkeep
@@ -0,0 +1,2 @@
+The brotli directory tests the workaround for an `ensurepip` bug in older Python versions:
+https://github.com/heroku/heroku-buildpack-python/issues/1697
diff --git a/spec/fixtures/poetry_oldest_python/poetry.lock b/spec/fixtures/poetry_oldest_python/poetry.lock
new file mode 100644
index 000000000..e8576cea7
--- /dev/null
+++ b/spec/fixtures/poetry_oldest_python/poetry.lock
@@ -0,0 +1,17 @@
+# This file is automatically @generated by Poetry 1.8.5 and should not be changed by hand.
+
+[[package]]
+name = "typing-extensions"
+version = "4.15.0"
+description = "Backported and Experimental Type Hints for Python 3.9+"
+optional = false
+python-versions = ">=3.9"
+files = [
+    {file = "typing_extensions-4.15.0-py3-none-any.whl", hash = "sha256:f0fa19c6845758ab08074a0cfa8b7aecb71c999ca73d62883bc25cc018c4e548"},
+    {file = "typing_extensions-4.15.0.tar.gz", hash = "sha256:0cea48d173cc12fa28ecabc3b837ea3cf6f38c6d1136f85cbaaf598984861466"},
+]
+
+[metadata]
+lock-version = "2.0"
+python-versions = "^3.10"
+content-hash = "cfec7fa4755d6e9851dbc7848a76babbc6c288c7f13cc2bed2e60f83783d4fd2"
diff --git a/spec/fixtures/poetry_oldest_python/pyproject.toml b/spec/fixtures/poetry_oldest_python/pyproject.toml
new file mode 100644
index 000000000..e193f693f
--- /dev/null
+++ b/spec/fixtures/poetry_oldest_python/pyproject.toml
@@ -0,0 +1,6 @@
+[tool.poetry]
+package-mode = false
+
+[tool.poetry.dependencies]
+python = "^3.10"
+typing-extensions = "*"
diff --git a/spec/fixtures/pyproject_toml_only/.example-dotfile b/spec/fixtures/pyproject_toml_only/.example-dotfile
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/pyproject_toml_only/pyproject.toml b/spec/fixtures/pyproject_toml_only/pyproject.toml
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/pyproject_toml_only/subdir/some-file b/spec/fixtures/pyproject_toml_only/subdir/some-file
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/python_3.10/.python-version b/spec/fixtures/python_3.10/.python-version
new file mode 100644
index 000000000..3aa278d1a
--- /dev/null
+++ b/spec/fixtures/python_3.10/.python-version
@@ -0,0 +1,2 @@
+# Comments are supported
+3.10
diff --git a/spec/fixtures/python_3.10/requirements.txt b/spec/fixtures/python_3.10/requirements.txt
index a42590beb..f6e499a84 100644
--- a/spec/fixtures/python_3.10/requirements.txt
+++ b/spec/fixtures/python_3.10/requirements.txt
@@ -1 +1,2 @@
-urllib3
+# This package has been picked since it has no dependencies and is small/fast to install.
+typing-extensions==4.15.0
diff --git a/spec/fixtures/python_3.10/runtime.txt b/spec/fixtures/python_3.10/runtime.txt
deleted file mode 100644
index 2bccd9d9d..000000000
--- a/spec/fixtures/python_3.10/runtime.txt
+++ /dev/null
@@ -1 +0,0 @@
-python-3.10.14
diff --git a/spec/fixtures/python_3.10_outdated/runtime.txt b/spec/fixtures/python_3.10_outdated/runtime.txt
deleted file mode 100644
index a5da7cc4d..000000000
--- a/spec/fixtures/python_3.10_outdated/runtime.txt
+++ /dev/null
@@ -1 +0,0 @@
-python-3.10.5
diff --git a/spec/fixtures/python_3.11/.python-version b/spec/fixtures/python_3.11/.python-version
new file mode 100644
index 000000000..576fc2bfe
--- /dev/null
+++ b/spec/fixtures/python_3.11/.python-version
@@ -0,0 +1,2 @@
+# Comments are supported
+3.11
diff --git a/spec/fixtures/python_3.11/requirements.txt b/spec/fixtures/python_3.11/requirements.txt
index a42590beb..f6e499a84 100644
--- a/spec/fixtures/python_3.11/requirements.txt
+++ b/spec/fixtures/python_3.11/requirements.txt
@@ -1 +1,2 @@
-urllib3
+# This package has been picked since it has no dependencies and is small/fast to install.
+typing-extensions==4.15.0
diff --git a/spec/fixtures/python_3.11/runtime.txt b/spec/fixtures/python_3.11/runtime.txt
deleted file mode 100644
index 546f3c8de..000000000
--- a/spec/fixtures/python_3.11/runtime.txt
+++ /dev/null
@@ -1 +0,0 @@
-python-3.11.9
diff --git a/spec/fixtures/python_3.11_outdated/runtime.txt b/spec/fixtures/python_3.11_outdated/runtime.txt
deleted file mode 100644
index 335156c09..000000000
--- a/spec/fixtures/python_3.11_outdated/runtime.txt
+++ /dev/null
@@ -1 +0,0 @@
-python-3.11.0
diff --git a/spec/fixtures/python_3.12/.python-version b/spec/fixtures/python_3.12/.python-version
new file mode 100644
index 000000000..936a75516
--- /dev/null
+++ b/spec/fixtures/python_3.12/.python-version
@@ -0,0 +1,2 @@
+# Comments are supported
+3.12
diff --git a/spec/fixtures/python_3.12/requirements.txt b/spec/fixtures/python_3.12/requirements.txt
index a42590beb..f6e499a84 100644
--- a/spec/fixtures/python_3.12/requirements.txt
+++ b/spec/fixtures/python_3.12/requirements.txt
@@ -1 +1,2 @@
-urllib3
+# This package has been picked since it has no dependencies and is small/fast to install.
+typing-extensions==4.15.0
diff --git a/spec/fixtures/python_3.12/runtime.txt b/spec/fixtures/python_3.12/runtime.txt
deleted file mode 100644
index 74d315a82..000000000
--- a/spec/fixtures/python_3.12/runtime.txt
+++ /dev/null
@@ -1 +0,0 @@
-python-3.12.4
diff --git a/spec/fixtures/python_3.12_outdated/runtime.txt b/spec/fixtures/python_3.12_outdated/runtime.txt
deleted file mode 100644
index 44f8fbe3a..000000000
--- a/spec/fixtures/python_3.12_outdated/runtime.txt
+++ /dev/null
@@ -1 +0,0 @@
-python-3.12.0
diff --git a/spec/fixtures/python_3.13/.python-version b/spec/fixtures/python_3.13/.python-version
new file mode 100644
index 000000000..d23c34390
--- /dev/null
+++ b/spec/fixtures/python_3.13/.python-version
@@ -0,0 +1,2 @@
+# Comments are supported
+3.13
diff --git a/spec/fixtures/python_3.13/requirements.txt b/spec/fixtures/python_3.13/requirements.txt
new file mode 100644
index 000000000..f6e499a84
--- /dev/null
+++ b/spec/fixtures/python_3.13/requirements.txt
@@ -0,0 +1,2 @@
+# This package has been picked since it has no dependencies and is small/fast to install.
+typing-extensions==4.15.0
diff --git a/spec/fixtures/python_3.14/.python-version b/spec/fixtures/python_3.14/.python-version
new file mode 100644
index 000000000..70dc33adb
--- /dev/null
+++ b/spec/fixtures/python_3.14/.python-version
@@ -0,0 +1,2 @@
+# Comments are supported
+3.14
diff --git a/spec/fixtures/python_3.14/requirements.txt b/spec/fixtures/python_3.14/requirements.txt
new file mode 100644
index 000000000..f6e499a84
--- /dev/null
+++ b/spec/fixtures/python_3.14/requirements.txt
@@ -0,0 +1,2 @@
+# This package has been picked since it has no dependencies and is small/fast to install.
+typing-extensions==4.15.0
diff --git a/spec/fixtures/python_3.6/requirements.txt b/spec/fixtures/python_3.6/requirements.txt
deleted file mode 100644
index a42590beb..000000000
--- a/spec/fixtures/python_3.6/requirements.txt
+++ /dev/null
@@ -1 +0,0 @@
-urllib3
diff --git a/spec/fixtures/python_3.6/runtime.txt b/spec/fixtures/python_3.6/runtime.txt
deleted file mode 100644
index 6aaad49f7..000000000
--- a/spec/fixtures/python_3.6/runtime.txt
+++ /dev/null
@@ -1 +0,0 @@
-python-3.6.15
diff --git a/spec/fixtures/python_3.7/requirements.txt b/spec/fixtures/python_3.7/requirements.txt
deleted file mode 100644
index a42590beb..000000000
--- a/spec/fixtures/python_3.7/requirements.txt
+++ /dev/null
@@ -1 +0,0 @@
-urllib3
diff --git a/spec/fixtures/python_3.7/runtime.txt b/spec/fixtures/python_3.7/runtime.txt
deleted file mode 100644
index 113b0bcca..000000000
--- a/spec/fixtures/python_3.7/runtime.txt
+++ /dev/null
@@ -1 +0,0 @@
-python-3.7.17
diff --git a/spec/fixtures/python_3.8/requirements.txt b/spec/fixtures/python_3.8/requirements.txt
deleted file mode 100644
index a42590beb..000000000
--- a/spec/fixtures/python_3.8/requirements.txt
+++ /dev/null
@@ -1 +0,0 @@
-urllib3
diff --git a/spec/fixtures/python_3.8/runtime.txt b/spec/fixtures/python_3.8/runtime.txt
deleted file mode 100644
index 96307d57b..000000000
--- a/spec/fixtures/python_3.8/runtime.txt
+++ /dev/null
@@ -1 +0,0 @@
-python-3.8.19
diff --git a/spec/fixtures/python_3.8_outdated/runtime.txt b/spec/fixtures/python_3.8_outdated/runtime.txt
deleted file mode 100644
index d9a16ae1e..000000000
--- a/spec/fixtures/python_3.8_outdated/runtime.txt
+++ /dev/null
@@ -1 +0,0 @@
-python-3.8.12
diff --git a/spec/fixtures/python_3.9/requirements.txt b/spec/fixtures/python_3.9/requirements.txt
deleted file mode 100644
index a42590beb..000000000
--- a/spec/fixtures/python_3.9/requirements.txt
+++ /dev/null
@@ -1 +0,0 @@
-urllib3
diff --git a/spec/fixtures/python_3.9/runtime.txt b/spec/fixtures/python_3.9/runtime.txt
deleted file mode 100644
index 4458b433c..000000000
--- a/spec/fixtures/python_3.9/runtime.txt
+++ /dev/null
@@ -1 +0,0 @@
-python-3.9.19
diff --git a/spec/fixtures/python_3.9_outdated/runtime.txt b/spec/fixtures/python_3.9_outdated/runtime.txt
deleted file mode 100644
index 540296197..000000000
--- a/spec/fixtures/python_3.9_outdated/runtime.txt
+++ /dev/null
@@ -1 +0,0 @@
-python-3.9.12
diff --git a/spec/fixtures/python_in_app_source/.heroku/python/bin/python b/spec/fixtures/python_in_app_source/.heroku/python/bin/python
new file mode 100644
index 000000000..04b03ed28
--- /dev/null
+++ b/spec/fixtures/python_in_app_source/.heroku/python/bin/python
@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+
+# This file emulates a Python install having been committed to the app's Git repo.
+# For example, by downloading a slug, extracting it, and committing the results.
+
+set -euo pipefail
+
+exit 0
diff --git a/spec/fixtures/python_in_app_source/.python-version b/spec/fixtures/python_in_app_source/.python-version
new file mode 100644
index 000000000..6324d401a
--- /dev/null
+++ b/spec/fixtures/python_in_app_source/.python-version
@@ -0,0 +1 @@
+3.14
diff --git a/spec/fixtures/python_in_app_source/requirements.txt b/spec/fixtures/python_in_app_source/requirements.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/python_version_eol/.python-version b/spec/fixtures/python_version_eol/.python-version
new file mode 100644
index 000000000..033763cdf
--- /dev/null
+++ b/spec/fixtures/python_version_eol/.python-version
@@ -0,0 +1,8 @@
+# Comments are supported.
+    # Even when indented
+#
+# So are empty lines, and leading/trailing whitespace.
+
+  
+  3.9  
+  
diff --git a/spec/fixtures/python_version_eol/requirements.txt b/spec/fixtures/python_version_eol/requirements.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/python_version_eol_cached/bin/pre_compile b/spec/fixtures/python_version_eol_cached/bin/pre_compile
new file mode 100755
index 000000000..63422ee0b
--- /dev/null
+++ b/spec/fixtures/python_version_eol_cached/bin/pre_compile
@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+# Emulate the cache from a previous build that used a now-EOL Python version.
+mkdir -p "${CACHE_DIR:?}/.heroku"
+echo "python-3.9.25" >"${CACHE_DIR}/.heroku/python-version"
diff --git a/spec/fixtures/python_version_eol_cached/requirements.txt b/spec/fixtures/python_version_eol_cached/requirements.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/python_version_file_invalid_version/.python-version b/spec/fixtures/python_version_file_invalid_version/.python-version
new file mode 100644
index 000000000..8641e5c56
--- /dev/null
+++ b/spec/fixtures/python_version_file_invalid_version/.python-version
@@ -0,0 +1,19 @@
+# Comments are supported.
+    # Even when indented
+#
+# So are empty lines, and leading/trailing whitespace.
+
+		# So are tabs
+		
+
+# So are CRLFs (this whole file has CRLF line endings)
+
+# This version should be ignored, since it's commented out
+# 2.7.18
+
+  # This version number has:
+  # - a leading zero width space character
+  # - a normal space and a non-breaking space in the middle
+  # - a trailing ESC control character (from an ANSI escape sequence) at the end
+  ​python -	 3.12.0  
+  
diff --git a/spec/fixtures/python_version_file_invalid_version/requirements.txt b/spec/fixtures/python_version_file_invalid_version/requirements.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/python_version_file_misspelled/.python-version b/spec/fixtures/python_version_file_misspelled/.python-version
new file mode 100644
index 000000000..6324d401a
--- /dev/null
+++ b/spec/fixtures/python_version_file_misspelled/.python-version
@@ -0,0 +1 @@
+3.14
diff --git a/spec/fixtures/python_version_file_misspelled/.python-version  b/spec/fixtures/python_version_file_misspelled/.python-version 
new file mode 100644
index 000000000..f7549fdca
--- /dev/null
+++ b/spec/fixtures/python_version_file_misspelled/.python-version 	
@@ -0,0 +1 @@
+# This file has a trailing space in its filename
diff --git a/spec/fixtures/python_version_file_misspelled/requirements.txt b/spec/fixtures/python_version_file_misspelled/requirements.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/python_version_file_multiple_versions/.python-version b/spec/fixtures/python_version_file_multiple_versions/.python-version
new file mode 100644
index 000000000..b5bdebd50
--- /dev/null
+++ b/spec/fixtures/python_version_file_multiple_versions/.python-version
@@ -0,0 +1,5 @@
+# Valid comment
+3.12
+  
+  # Indentation should be stripped in the error message
+  2.7  
diff --git a/spec/fixtures/python_version_file_multiple_versions/requirements.txt b/spec/fixtures/python_version_file_multiple_versions/requirements.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/python_version_file_no_version/.python-version b/spec/fixtures/python_version_file_no_version/.python-version
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/python_version_file_no_version/requirements.txt b/spec/fixtures/python_version_file_no_version/requirements.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/python_version_file_unsupported_encoding/.python-version b/spec/fixtures/python_version_file_unsupported_encoding/.python-version
new file mode 100644
index 000000000..adc7314b0
--- /dev/null
+++ b/spec/fixtures/python_version_file_unsupported_encoding/.python-version
@@ -0,0 +1,2 @@
+# This file is saved with the encoding: UTF-8 with BOM
+3.12
diff --git a/spec/fixtures/python_version_file_unsupported_encoding/requirements.txt b/spec/fixtures/python_version_file_unsupported_encoding/requirements.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/python_version_invalid/runtime.txt b/spec/fixtures/python_version_invalid/runtime.txt
deleted file mode 100644
index 504402610..000000000
--- a/spec/fixtures/python_version_invalid/runtime.txt
+++ /dev/null
@@ -1 +0,0 @@
-python-3.12.0invalid
diff --git a/spec/fixtures/python_version_non_existent_major/.python-version b/spec/fixtures/python_version_non_existent_major/.python-version
new file mode 100644
index 000000000..f1f7e4608
--- /dev/null
+++ b/spec/fixtures/python_version_non_existent_major/.python-version
@@ -0,0 +1 @@
+3.999
diff --git a/spec/fixtures/python_version_non_existent_major/requirements.txt b/spec/fixtures/python_version_non_existent_major/requirements.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/python_version_non_existent_major_cached/bin/pre_compile b/spec/fixtures/python_version_non_existent_major_cached/bin/pre_compile
new file mode 100755
index 000000000..1075c4857
--- /dev/null
+++ b/spec/fixtures/python_version_non_existent_major_cached/bin/pre_compile
@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+# Emulate the cache from a previous build which used a newer default Python version
+# than the version supported by this buildpack version.
+mkdir -p "${CACHE_DIR:?}/.heroku"
+echo "python-3.99.0" >"${CACHE_DIR}/.heroku/python-version"
diff --git a/spec/fixtures/python_version_non_existent_major_cached/requirements.txt b/spec/fixtures/python_version_non_existent_major_cached/requirements.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/python_version_non_existent_patch/.python-version b/spec/fixtures/python_version_non_existent_patch/.python-version
new file mode 100644
index 000000000..bb40ea005
--- /dev/null
+++ b/spec/fixtures/python_version_non_existent_patch/.python-version
@@ -0,0 +1 @@
+3.12.999
diff --git a/spec/fixtures/python_version_non_existent_patch/requirements.txt b/spec/fixtures/python_version_non_existent_patch/requirements.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/python_version_outdated/.python-version b/spec/fixtures/python_version_outdated/.python-version
new file mode 100644
index 000000000..f982feb41
--- /dev/null
+++ b/spec/fixtures/python_version_outdated/.python-version
@@ -0,0 +1 @@
+3.14.0
diff --git a/spec/fixtures/python_version_outdated/requirements.txt b/spec/fixtures/python_version_outdated/requirements.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/python_version_unspecified/requirements.txt b/spec/fixtures/python_version_unspecified/requirements.txt
index a42590beb..f6e499a84 100644
--- a/spec/fixtures/python_version_unspecified/requirements.txt
+++ b/spec/fixtures/python_version_unspecified/requirements.txt
@@ -1 +1,2 @@
-urllib3
+# This package has been picked since it has no dependencies and is small/fast to install.
+typing-extensions==4.15.0
diff --git a/spec/fixtures/requirements_compiled/requirements.txt b/spec/fixtures/requirements_compiled/requirements.txt
deleted file mode 100644
index 2331d3f79..000000000
--- a/spec/fixtures/requirements_compiled/requirements.txt
+++ /dev/null
@@ -1,6 +0,0 @@
-# Packages that rely on headers from the stack image (depending on wheel availability).
-cffi
-mysqlclient
-psycopg2
-pylibmc
-pysqlite3
diff --git a/spec/fixtures/requirements_editable/packages/local_package_pyproject_toml/local_package_pyproject_toml/__init__.py b/spec/fixtures/requirements_editable/packages/local_package_pyproject_toml/local_package_pyproject_toml/__init__.py
deleted file mode 100644
index b86d791d2..000000000
--- a/spec/fixtures/requirements_editable/packages/local_package_pyproject_toml/local_package_pyproject_toml/__init__.py
+++ /dev/null
@@ -1,2 +0,0 @@
-def hello():
-    print("Hello pyproject.toml!")
diff --git a/spec/fixtures/requirements_editable/packages/local_package_setup_py/local_package_setup_py/__init__.py b/spec/fixtures/requirements_editable/packages/local_package_setup_py/local_package_setup_py/__init__.py
deleted file mode 100644
index e98d42373..000000000
--- a/spec/fixtures/requirements_editable/packages/local_package_setup_py/local_package_setup_py/__init__.py
+++ /dev/null
@@ -1,2 +0,0 @@
-def hello():
-    print("Hello setup.py!")
diff --git a/spec/fixtures/requirements_git/requirements.txt b/spec/fixtures/requirements_git/requirements.txt
deleted file mode 100644
index 81e9dbfe0..000000000
--- a/spec/fixtures/requirements_git/requirements.txt
+++ /dev/null
@@ -1,2 +0,0 @@
-# This relies upon the VCS binaries from the stack image.
-git+https://github.com/certifi/python-certifi
diff --git a/spec/fixtures/requirements_txt_and_setup_py/requirements.txt b/spec/fixtures/requirements_txt_and_setup_py/requirements.txt
deleted file mode 100644
index a42590beb..000000000
--- a/spec/fixtures/requirements_txt_and_setup_py/requirements.txt
+++ /dev/null
@@ -1 +0,0 @@
-urllib3
diff --git a/spec/fixtures/requirements_txt_and_setup_py/setup.py b/spec/fixtures/requirements_txt_and_setup_py/setup.py
deleted file mode 100644
index 8d636d69a..000000000
--- a/spec/fixtures/requirements_txt_and_setup_py/setup.py
+++ /dev/null
@@ -1,6 +0,0 @@
-from setuptools import setup
-
-setup(
-  name='test',
-  install_requires=['six'],
-)
diff --git a/spec/fixtures/runtime_txt_and_python_version_file/.python-version b/spec/fixtures/runtime_txt_and_python_version_file/.python-version
new file mode 100644
index 000000000..154e97ed3
--- /dev/null
+++ b/spec/fixtures/runtime_txt_and_python_version_file/.python-version
@@ -0,0 +1,2 @@
+# The version in runtime.txt should take precedence over this.
+3.9
diff --git a/spec/fixtures/runtime_txt_and_python_version_file/requirements.txt b/spec/fixtures/runtime_txt_and_python_version_file/requirements.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/runtime_txt_and_python_version_file/runtime.txt b/spec/fixtures/runtime_txt_and_python_version_file/runtime.txt
new file mode 100644
index 000000000..354250f94
--- /dev/null
+++ b/spec/fixtures/runtime_txt_and_python_version_file/runtime.txt
@@ -0,0 +1,8 @@
+# Comments are supported
+    # Even when indented
+
+# This version should be ignored, since it's commented out
+# 2.7.18
+ 
+  python-3.13  
+ 
\ No newline at end of file
diff --git a/spec/fixtures/runtime_txt_eol_version/requirements.txt b/spec/fixtures/runtime_txt_eol_version/requirements.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/runtime_txt_eol_version/runtime.txt b/spec/fixtures/runtime_txt_eol_version/runtime.txt
new file mode 100644
index 000000000..586b67310
--- /dev/null
+++ b/spec/fixtures/runtime_txt_eol_version/runtime.txt
@@ -0,0 +1 @@
+python-2.7.18
diff --git a/spec/fixtures/runtime_txt_invalid_version/requirements.txt b/spec/fixtures/runtime_txt_invalid_version/requirements.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/fixtures/runtime_txt_invalid_version/runtime.txt b/spec/fixtures/runtime_txt_invalid_version/runtime.txt
new file mode 100644
index 000000000..75986f4ed
Binary files /dev/null and b/spec/fixtures/runtime_txt_invalid_version/runtime.txt differ
diff --git a/spec/fixtures/runtime_txt_only/runtime.txt b/spec/fixtures/runtime_txt_only/runtime.txt
deleted file mode 100644
index 74d315a82..000000000
--- a/spec/fixtures/runtime_txt_only/runtime.txt
+++ /dev/null
@@ -1 +0,0 @@
-python-3.12.4
diff --git a/spec/fixtures/runtime_txt_with_stray_whitespace/requirements.txt b/spec/fixtures/runtime_txt_with_stray_whitespace/requirements.txt
deleted file mode 100644
index a42590beb..000000000
--- a/spec/fixtures/runtime_txt_with_stray_whitespace/requirements.txt
+++ /dev/null
@@ -1 +0,0 @@
-urllib3
diff --git a/spec/fixtures/runtime_txt_with_stray_whitespace/runtime.txt b/spec/fixtures/runtime_txt_with_stray_whitespace/runtime.txt
deleted file mode 100644
index eb7c2eafb..000000000
--- a/spec/fixtures/runtime_txt_with_stray_whitespace/runtime.txt
+++ /dev/null
@@ -1,3 +0,0 @@
- 
- python-3.12.4 
- 
\ No newline at end of file
diff --git a/spec/fixtures/setup_py_only/.python-version b/spec/fixtures/setup_py_only/.python-version
new file mode 100644
index 000000000..6324d401a
--- /dev/null
+++ b/spec/fixtures/setup_py_only/.python-version
@@ -0,0 +1 @@
+3.14
diff --git a/spec/fixtures/setup_py_only/setup.py b/spec/fixtures/setup_py_only/setup.py
index 8d636d69a..e69de29bb 100644
--- a/spec/fixtures/setup_py_only/setup.py
+++ b/spec/fixtures/setup_py_only/setup.py
@@ -1,6 +0,0 @@
-from setuptools import setup
-
-setup(
-  name='test',
-  install_requires=['six'],
-)
diff --git a/spec/fixtures/uv_basic/.python-version b/spec/fixtures/uv_basic/.python-version
new file mode 100644
index 000000000..6324d401a
--- /dev/null
+++ b/spec/fixtures/uv_basic/.python-version
@@ -0,0 +1 @@
+3.14
diff --git a/spec/fixtures/uv_basic/bin/compile b/spec/fixtures/uv_basic/bin/compile
new file mode 100755
index 000000000..5a6fb09f4
--- /dev/null
+++ b/spec/fixtures/uv_basic/bin/compile
@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack, and tests that the environment is
+# configured as expected for buildpacks that run after the Python buildpack.
+
+set -euo pipefail
+
+BUILD_DIR="${1}"
+CACHE_DIR="${2}"
+
+cd "${BUILD_DIR}"
+
+bin/print-env-vars.sh
+echo
+
+python -c 'import pprint, sys; pprint.pp(sys.path)'
+echo
+
+uv --version
+uv pip list
+echo
+
+python -c 'import typing_extensions; print(typing_extensions)'
+echo
+
+jq --sort-keys '.' "${CACHE_DIR}/build-data/python.json"
diff --git a/spec/fixtures/uv_basic/bin/detect b/spec/fixtures/uv_basic/bin/detect
new file mode 100755
index 000000000..68cdcc4a2
--- /dev/null
+++ b/spec/fixtures/uv_basic/bin/detect
@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack.
+
+set -euo pipefail
+
+echo "Inline"
diff --git a/spec/fixtures/uv_basic/bin/post_compile b/spec/fixtures/uv_basic/bin/post_compile
new file mode 100644
index 000000000..15dc8c2f3
--- /dev/null
+++ b/spec/fixtures/uv_basic/bin/post_compile
@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+# This intentionally uses a relative path to test that the CWD is correct.
+exec bin/print-env-vars.sh
diff --git a/spec/fixtures/uv_basic/bin/print-env-vars.sh b/spec/fixtures/uv_basic/bin/print-env-vars.sh
new file mode 100755
index 000000000..ebc9ad735
--- /dev/null
+++ b/spec/fixtures/uv_basic/bin/print-env-vars.sh
@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+printenv | sort | grep -vE '^(_|BUILDPACK_LOG_FILE|DYNO|HOME|OLDPWD|PORT|PS1|PWD|REQUEST_ID|SHLVL|SOURCE_VERSION|STACK|TERM)='
diff --git a/spec/fixtures/uv_basic/pyproject.toml b/spec/fixtures/uv_basic/pyproject.toml
new file mode 100644
index 000000000..b0b1ffa60
--- /dev/null
+++ b/spec/fixtures/uv_basic/pyproject.toml
@@ -0,0 +1,13 @@
+[project]
+name = "uv-basic"
+version = "0.0.0"
+requires-python = ">=3.14"
+dependencies = [
+    "typing-extensions",
+]
+
+[dependency-groups]
+# This group shouldn't be installed due to us passing `--no-default-groups`.
+dev = [
+    "pytest",
+]
diff --git a/spec/fixtures/uv_basic/uv.lock b/spec/fixtures/uv_basic/uv.lock
new file mode 100644
index 000000000..163be6bca
--- /dev/null
+++ b/spec/fixtures/uv_basic/uv.lock
@@ -0,0 +1,92 @@
+version = 1
+revision = 3
+requires-python = ">=3.14"
+
+[[package]]
+name = "colorama"
+version = "0.4.6"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/d8/53/6f443c9a4a8358a93a6792e2acffb9d9d5cb0a5cfd8802644b7b1c9a02e4/colorama-0.4.6.tar.gz", hash = "sha256:08695f5cb7ed6e0531a20572697297273c47b8cae5a63ffc6d6ed5c201be6e44", size = 27697, upload-time = "2022-10-25T02:36:22.414Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/d1/d6/3965ed04c63042e047cb6a3e6ed1a63a35087b6a609aa3a15ed8ac56c221/colorama-0.4.6-py2.py3-none-any.whl", hash = "sha256:4f1d9991f5acc0ca119f9d443620b77f9d6b33703e51011c16baf57afb285fc6", size = 25335, upload-time = "2022-10-25T02:36:20.889Z" },
+]
+
+[[package]]
+name = "iniconfig"
+version = "2.3.0"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/72/34/14ca021ce8e5dfedc35312d08ba8bf51fdd999c576889fc2c24cb97f4f10/iniconfig-2.3.0.tar.gz", hash = "sha256:c76315c77db068650d49c5b56314774a7804df16fee4402c1f19d6d15d8c4730", size = 20503, upload-time = "2025-10-18T21:55:43.219Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/cb/b1/3846dd7f199d53cb17f49cba7e651e9ce294d8497c8c150530ed11865bb8/iniconfig-2.3.0-py3-none-any.whl", hash = "sha256:f631c04d2c48c52b84d0d0549c99ff3859c98df65b3101406327ecc7d53fbf12", size = 7484, upload-time = "2025-10-18T21:55:41.639Z" },
+]
+
+[[package]]
+name = "packaging"
+version = "25.0"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/a1/d4/1fc4078c65507b51b96ca8f8c3ba19e6a61c8253c72794544580a7b6c24d/packaging-25.0.tar.gz", hash = "sha256:d443872c98d677bf60f6a1f2f8c1cb748e8fe762d2bf9d3148b5599295b0fc4f", size = 165727, upload-time = "2025-04-19T11:48:59.673Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/20/12/38679034af332785aac8774540895e234f4d07f7545804097de4b666afd8/packaging-25.0-py3-none-any.whl", hash = "sha256:29572ef2b1f17581046b3a2227d5c611fb25ec70ca1ba8554b24b0e69331a484", size = 66469, upload-time = "2025-04-19T11:48:57.875Z" },
+]
+
+[[package]]
+name = "pluggy"
+version = "1.6.0"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/f9/e2/3e91f31a7d2b083fe6ef3fa267035b518369d9511ffab804f839851d2779/pluggy-1.6.0.tar.gz", hash = "sha256:7dcc130b76258d33b90f61b658791dede3486c3e6bfb003ee5c9bfb396dd22f3", size = 69412, upload-time = "2025-05-15T12:30:07.975Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/54/20/4d324d65cc6d9205fabedc306948156824eb9f0ee1633355a8f7ec5c66bf/pluggy-1.6.0-py3-none-any.whl", hash = "sha256:e920276dd6813095e9377c0bc5566d94c932c33b27a3e3945d8389c374dd4746", size = 20538, upload-time = "2025-05-15T12:30:06.134Z" },
+]
+
+[[package]]
+name = "pygments"
+version = "2.19.2"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/b0/77/a5b8c569bf593b0140bde72ea885a803b82086995367bf2037de0159d924/pygments-2.19.2.tar.gz", hash = "sha256:636cb2477cec7f8952536970bc533bc43743542f70392ae026374600add5b887", size = 4968631, upload-time = "2025-06-21T13:39:12.283Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/c7/21/705964c7812476f378728bdf590ca4b771ec72385c533964653c68e86bdc/pygments-2.19.2-py3-none-any.whl", hash = "sha256:86540386c03d588bb81d44bc3928634ff26449851e99741617ecb9037ee5ec0b", size = 1225217, upload-time = "2025-06-21T13:39:07.939Z" },
+]
+
+[[package]]
+name = "pytest"
+version = "9.0.1"
+source = { registry = "https://pypi.org/simple" }
+dependencies = [
+    { name = "colorama", marker = "sys_platform == 'win32'" },
+    { name = "iniconfig" },
+    { name = "packaging" },
+    { name = "pluggy" },
+    { name = "pygments" },
+]
+sdist = { url = "https://files.pythonhosted.org/packages/07/56/f013048ac4bc4c1d9be45afd4ab209ea62822fb1598f40687e6bf45dcea4/pytest-9.0.1.tar.gz", hash = "sha256:3e9c069ea73583e255c3b21cf46b8d3c56f6e3a1a8f6da94ccb0fcf57b9d73c8", size = 1564125, upload-time = "2025-11-12T13:05:09.333Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/0b/8b/6300fb80f858cda1c51ffa17075df5d846757081d11ab4aa35cef9e6258b/pytest-9.0.1-py3-none-any.whl", hash = "sha256:67be0030d194df2dfa7b556f2e56fb3c3315bd5c8822c6951162b92b32ce7dad", size = 373668, upload-time = "2025-11-12T13:05:07.379Z" },
+]
+
+[[package]]
+name = "typing-extensions"
+version = "4.15.0"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/72/94/1a15dd82efb362ac84269196e94cf00f187f7ed21c242792a923cdb1c61f/typing_extensions-4.15.0.tar.gz", hash = "sha256:0cea48d173cc12fa28ecabc3b837ea3cf6f38c6d1136f85cbaaf598984861466", size = 109391, upload-time = "2025-08-25T13:49:26.313Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/18/67/36e9267722cc04a6b9f15c7f3441c2363321a3ea07da7ae0c0707beb2a9c/typing_extensions-4.15.0-py3-none-any.whl", hash = "sha256:f0fa19c6845758ab08074a0cfa8b7aecb71c999ca73d62883bc25cc018c4e548", size = 44614, upload-time = "2025-08-25T13:49:24.86Z" },
+]
+
+[[package]]
+name = "uv-basic"
+version = "0.0.0"
+source = { virtual = "." }
+dependencies = [
+    { name = "typing-extensions" },
+]
+
+[package.dev-dependencies]
+dev = [
+    { name = "pytest" },
+]
+
+[package.metadata]
+requires-dist = [{ name = "typing-extensions" }]
+
+[package.metadata.requires-dev]
+dev = [{ name = "pytest" }]
diff --git a/spec/fixtures/uv_editable/.python-version b/spec/fixtures/uv_editable/.python-version
new file mode 100644
index 000000000..6324d401a
--- /dev/null
+++ b/spec/fixtures/uv_editable/.python-version
@@ -0,0 +1 @@
+3.14
diff --git a/spec/fixtures/uv_editable/bin/compile b/spec/fixtures/uv_editable/bin/compile
new file mode 100755
index 000000000..df17e9401
--- /dev/null
+++ b/spec/fixtures/uv_editable/bin/compile
@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack, and tests that editable requirements are
+# usable by buildpacks that run after the Python buildpack during the build.
+
+set -euo pipefail
+
+BUILD_DIR="${1}"
+
+cd "${BUILD_DIR}"
+
+exec bin/test-entrypoints.sh
diff --git a/spec/fixtures/uv_editable/bin/detect b/spec/fixtures/uv_editable/bin/detect
new file mode 100755
index 000000000..68cdcc4a2
--- /dev/null
+++ b/spec/fixtures/uv_editable/bin/detect
@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack.
+
+set -euo pipefail
+
+echo "Inline"
diff --git a/spec/fixtures/uv_editable/bin/post_compile b/spec/fixtures/uv_editable/bin/post_compile
new file mode 100755
index 000000000..6e77d159a
--- /dev/null
+++ b/spec/fixtures/uv_editable/bin/post_compile
@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+exec bin/test-entrypoints.sh
diff --git a/spec/fixtures/pipenv_editable/bin/test-entrypoints b/spec/fixtures/uv_editable/bin/test-entrypoints.sh
similarity index 60%
rename from spec/fixtures/pipenv_editable/bin/test-entrypoints
rename to spec/fixtures/uv_editable/bin/test-entrypoints.sh
index 4c27ba0f4..2d7fab200 100755
--- a/spec/fixtures/pipenv_editable/bin/test-entrypoints
+++ b/spec/fixtures/uv_editable/bin/test-entrypoints.sh
@@ -4,10 +4,13 @@ set -euo pipefail
 
 cd .heroku/python/lib/python*/site-packages/
 
-# List any path like strings in .egg-link, .pth, and finder files in site-packages.
-grep --extended-regexp --only-matching -- '/\S+' *.egg-link *.pth __editable___*_finder.py | sort
+# List any path like strings in the .pth and finder files in site-packages.
+grep --extended-regexp --only-matching -- '/\S+' *.pth __editable___*_finder.py | sort
 echo
 
+echo -n "Running entrypoint for the current package: "
+uv-editable
+
 echo -n "Running entrypoint for the pyproject.toml-based local package: "
 local_package_pyproject_toml
 
diff --git a/spec/fixtures/uv_editable/packages/local_package_pyproject_toml/local_package_pyproject_toml/__init__.py b/spec/fixtures/uv_editable/packages/local_package_pyproject_toml/local_package_pyproject_toml/__init__.py
new file mode 100644
index 000000000..6ce02c341
--- /dev/null
+++ b/spec/fixtures/uv_editable/packages/local_package_pyproject_toml/local_package_pyproject_toml/__init__.py
@@ -0,0 +1,2 @@
+def hello():
+    print("Hello from pyproject.toml!")
diff --git a/spec/fixtures/uv_editable/packages/local_package_pyproject_toml/pyproject.toml b/spec/fixtures/uv_editable/packages/local_package_pyproject_toml/pyproject.toml
new file mode 100644
index 000000000..f567c3777
--- /dev/null
+++ b/spec/fixtures/uv_editable/packages/local_package_pyproject_toml/pyproject.toml
@@ -0,0 +1,6 @@
+[project]
+name = "local_package_pyproject_toml"
+version = "0.0.1"
+
+[project.scripts]
+local_package_pyproject_toml = "local_package_pyproject_toml:hello"
diff --git a/spec/fixtures/uv_editable/packages/local_package_setup_py/local_package_setup_py/__init__.py b/spec/fixtures/uv_editable/packages/local_package_setup_py/local_package_setup_py/__init__.py
new file mode 100644
index 000000000..8dccb8a0c
--- /dev/null
+++ b/spec/fixtures/uv_editable/packages/local_package_setup_py/local_package_setup_py/__init__.py
@@ -0,0 +1,2 @@
+def hello():
+    print("Hello from setup.py!")
diff --git a/spec/fixtures/uv_editable/packages/local_package_setup_py/setup.cfg b/spec/fixtures/uv_editable/packages/local_package_setup_py/setup.cfg
new file mode 100644
index 000000000..eff513964
--- /dev/null
+++ b/spec/fixtures/uv_editable/packages/local_package_setup_py/setup.cfg
@@ -0,0 +1,10 @@
+[metadata]
+name = local_package_setup_py
+version = 0.0.1
+
+[options]
+packages = local_package_setup_py
+
+[options.entry_points]
+console_scripts =
+    local_package_setup_py = local_package_setup_py:hello
diff --git a/spec/fixtures/uv_editable/packages/local_package_setup_py/setup.py b/spec/fixtures/uv_editable/packages/local_package_setup_py/setup.py
new file mode 100644
index 000000000..606849326
--- /dev/null
+++ b/spec/fixtures/uv_editable/packages/local_package_setup_py/setup.py
@@ -0,0 +1,3 @@
+from setuptools import setup
+
+setup()
diff --git a/spec/fixtures/uv_editable/pyproject.toml b/spec/fixtures/uv_editable/pyproject.toml
new file mode 100644
index 000000000..15a7b2365
--- /dev/null
+++ b/spec/fixtures/uv_editable/pyproject.toml
@@ -0,0 +1,25 @@
+[project]
+name = "uv-editable"
+version = "0.0.0"
+requires-python = ">=3.14"
+dependencies = [
+    "gunicorn",
+    "local-package-pyproject-toml",
+    "local-package-setup-py",
+]
+
+[project.scripts]
+uv-editable = "uv_editable:main"
+
+[build-system]
+requires = ["uv_build"]
+build-backend = "uv_build"
+
+[tool.uv.sources]
+# uv doesn't support editable mode with VCS dependencies:
+# https://github.com/astral-sh/uv/issues/5442
+# If that ever changes, we should switch to `editable = true` for gunicorn too.
+# We still include the Git gunicorn dependency here to ensure we have VCS coverage.
+gunicorn = { git = "https://github.com/benoitc/gunicorn" }
+local-package-pyproject-toml = { path = "packages/local_package_pyproject_toml", editable = true }
+local-package-setup-py = { path = "packages/local_package_setup_py", editable = true }
diff --git a/spec/fixtures/uv_editable/src/uv_editable/__init__.py b/spec/fixtures/uv_editable/src/uv_editable/__init__.py
new file mode 100644
index 000000000..ae2b5f267
--- /dev/null
+++ b/spec/fixtures/uv_editable/src/uv_editable/__init__.py
@@ -0,0 +1,2 @@
+def main() -> None:
+    print("Hello from uv-editable!")
diff --git a/spec/fixtures/uv_editable/uv.lock b/spec/fixtures/uv_editable/uv.lock
new file mode 100644
index 000000000..506143ee7
--- /dev/null
+++ b/spec/fixtures/uv_editable/uv.lock
@@ -0,0 +1,47 @@
+version = 1
+revision = 3
+requires-python = ">=3.14"
+
+[[package]]
+name = "gunicorn"
+version = "23.0.0"
+source = { git = "https://github.com/benoitc/gunicorn#56b5ad87f8d72a674145c273ed8f547513c2b409" }
+dependencies = [
+    { name = "packaging" },
+]
+
+[[package]]
+name = "local-package-pyproject-toml"
+version = "0.0.1"
+source = { editable = "packages/local_package_pyproject_toml" }
+
+[[package]]
+name = "local-package-setup-py"
+version = "0.0.1"
+source = { editable = "packages/local_package_setup_py" }
+
+[[package]]
+name = "packaging"
+version = "25.0"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/a1/d4/1fc4078c65507b51b96ca8f8c3ba19e6a61c8253c72794544580a7b6c24d/packaging-25.0.tar.gz", hash = "sha256:d443872c98d677bf60f6a1f2f8c1cb748e8fe762d2bf9d3148b5599295b0fc4f", size = 165727, upload-time = "2025-04-19T11:48:59.673Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/20/12/38679034af332785aac8774540895e234f4d07f7545804097de4b666afd8/packaging-25.0-py3-none-any.whl", hash = "sha256:29572ef2b1f17581046b3a2227d5c611fb25ec70ca1ba8554b24b0e69331a484", size = 66469, upload-time = "2025-04-19T11:48:57.875Z" },
+]
+
+[[package]]
+name = "uv-editable"
+version = "0.0.0"
+source = { editable = "." }
+dependencies = [
+    { name = "gunicorn" },
+    { name = "local-package-pyproject-toml" },
+    { name = "local-package-setup-py" },
+]
+
+[package.metadata]
+requires-dist = [
+    { name = "gunicorn", git = "https://github.com/benoitc/gunicorn" },
+    { name = "local-package-pyproject-toml", editable = "packages/local_package_pyproject_toml" },
+    { name = "local-package-setup-py", editable = "packages/local_package_setup_py" },
+]
diff --git a/spec/fixtures/uv_lockfile_out_of_sync/.python-version b/spec/fixtures/uv_lockfile_out_of_sync/.python-version
new file mode 100644
index 000000000..6324d401a
--- /dev/null
+++ b/spec/fixtures/uv_lockfile_out_of_sync/.python-version
@@ -0,0 +1 @@
+3.14
diff --git a/spec/fixtures/uv_lockfile_out_of_sync/pyproject.toml b/spec/fixtures/uv_lockfile_out_of_sync/pyproject.toml
new file mode 100644
index 000000000..8bd3574b4
--- /dev/null
+++ b/spec/fixtures/uv_lockfile_out_of_sync/pyproject.toml
@@ -0,0 +1,9 @@
+[project]
+name = "uv-lockfile-out-of-sync"
+version = "0.0.0"
+requires-python = ">=3.14"
+
+# This dependency isn't in the lockfile.
+dependencies = [
+    "typing-extensions",
+]
diff --git a/spec/fixtures/uv_lockfile_out_of_sync/uv.lock b/spec/fixtures/uv_lockfile_out_of_sync/uv.lock
new file mode 100644
index 000000000..50a8225c6
--- /dev/null
+++ b/spec/fixtures/uv_lockfile_out_of_sync/uv.lock
@@ -0,0 +1,8 @@
+version = 1
+revision = 3
+requires-python = ">=3.14"
+
+[[package]]
+name = "uv-lockfile-out-of-sync"
+version = "0.0.0"
+source = { virtual = "." }
diff --git a/spec/fixtures/uv_mismatched_python_version/.python-version b/spec/fixtures/uv_mismatched_python_version/.python-version
new file mode 100644
index 000000000..88c9ebc82
--- /dev/null
+++ b/spec/fixtures/uv_mismatched_python_version/.python-version
@@ -0,0 +1,2 @@
+# The version here intentionally doesn't match requires-python in pyproject.toml
+3.13
diff --git a/spec/fixtures/uv_mismatched_python_version/pyproject.toml b/spec/fixtures/uv_mismatched_python_version/pyproject.toml
new file mode 100644
index 000000000..b93af5953
--- /dev/null
+++ b/spec/fixtures/uv_mismatched_python_version/pyproject.toml
@@ -0,0 +1,9 @@
+[project]
+name = "uv-mismatched-python-version"
+version = "0.0.0"
+# The Python version here intentionally:
+# - Doesn't match the version in .python-version
+# - Matches the distro Python version in Ubuntu 24.04
+# ...so we can test both the error message and that uv doesn't fall back to system Python.
+requires-python = "==3.12.*"
+dependencies = []
diff --git a/spec/fixtures/uv_mismatched_python_version/uv.lock b/spec/fixtures/uv_mismatched_python_version/uv.lock
new file mode 100644
index 000000000..5982e7c5e
--- /dev/null
+++ b/spec/fixtures/uv_mismatched_python_version/uv.lock
@@ -0,0 +1,8 @@
+version = 1
+revision = 3
+requires-python = "==3.12.*"
+
+[[package]]
+name = "uv-mismatched-python-version"
+version = "0.0.0"
+source = { virtual = "." }
diff --git a/spec/fixtures/uv_no_python_version_file/pyproject.toml b/spec/fixtures/uv_no_python_version_file/pyproject.toml
new file mode 100644
index 000000000..dce78d6ba
--- /dev/null
+++ b/spec/fixtures/uv_no_python_version_file/pyproject.toml
@@ -0,0 +1,9 @@
+[project]
+name = "uv-no-python-version-file"
+version = "0.0.0"
+# The Python version here intentionally:
+# - Doesn't match the buildpack's default Python version
+# - Matches the distro Python version in Ubuntu 24.04
+# ...so we can test both the error message and that uv doesn't fall back to system Python.
+requires-python = "==3.12.*"
+dependencies = []
diff --git a/spec/fixtures/uv_no_python_version_file/uv.lock b/spec/fixtures/uv_no_python_version_file/uv.lock
new file mode 100644
index 000000000..b1a4d90e0
--- /dev/null
+++ b/spec/fixtures/uv_no_python_version_file/uv.lock
@@ -0,0 +1,8 @@
+version = 1
+revision = 3
+requires-python = "==3.12.*"
+
+[[package]]
+name = "uv-no-python-version-file"
+version = "0.0.0"
+source = { virtual = "." }
diff --git a/spec/fixtures/uv_oldest_python/.python-version b/spec/fixtures/uv_oldest_python/.python-version
new file mode 100644
index 000000000..30291cba2
--- /dev/null
+++ b/spec/fixtures/uv_oldest_python/.python-version
@@ -0,0 +1 @@
+3.10.0
diff --git a/spec/fixtures/uv_oldest_python/pyproject.toml b/spec/fixtures/uv_oldest_python/pyproject.toml
new file mode 100644
index 000000000..bf4f99549
--- /dev/null
+++ b/spec/fixtures/uv_oldest_python/pyproject.toml
@@ -0,0 +1,7 @@
+[project]
+name = "uv-oldest-python"
+version = "0.0.0"
+requires-python = "==3.10.*"
+dependencies = [
+    "typing-extensions",
+]
diff --git a/spec/fixtures/uv_oldest_python/uv.lock b/spec/fixtures/uv_oldest_python/uv.lock
new file mode 100644
index 000000000..47873756d
--- /dev/null
+++ b/spec/fixtures/uv_oldest_python/uv.lock
@@ -0,0 +1,23 @@
+version = 1
+revision = 2
+requires-python = "==3.10.*"
+
+[[package]]
+name = "typing-extensions"
+version = "4.15.0"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/72/94/1a15dd82efb362ac84269196e94cf00f187f7ed21c242792a923cdb1c61f/typing_extensions-4.15.0.tar.gz", hash = "sha256:0cea48d173cc12fa28ecabc3b837ea3cf6f38c6d1136f85cbaaf598984861466", size = 109391, upload-time = "2025-08-25T13:49:26.313Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/18/67/36e9267722cc04a6b9f15c7f3441c2363321a3ea07da7ae0c0707beb2a9c/typing_extensions-4.15.0-py3-none-any.whl", hash = "sha256:f0fa19c6845758ab08074a0cfa8b7aecb71c999ca73d62883bc25cc018c4e548", size = 44614, upload-time = "2025-08-25T13:49:24.86Z" },
+]
+
+[[package]]
+name = "uv-oldest-python"
+version = "0.0.0"
+source = { virtual = "." }
+dependencies = [
+    { name = "typing-extensions" },
+]
+
+[package.metadata]
+requires-dist = [{ name = "typing-extensions" }]
diff --git a/spec/fixtures/uv_runtime_txt/.python-version b/spec/fixtures/uv_runtime_txt/.python-version
new file mode 100644
index 000000000..1be10d256
--- /dev/null
+++ b/spec/fixtures/uv_runtime_txt/.python-version
@@ -0,0 +1,5 @@
+# The Python version here intentionally:
+# - Doesn't match that in runtime.txt
+# - Matches the distro Python version in Ubuntu 24.04
+# ...so we can test both the error message and that uv doesn't fall back to system Python.
+3.12
diff --git a/spec/fixtures/uv_runtime_txt/pyproject.toml b/spec/fixtures/uv_runtime_txt/pyproject.toml
new file mode 100644
index 000000000..c8f057a16
--- /dev/null
+++ b/spec/fixtures/uv_runtime_txt/pyproject.toml
@@ -0,0 +1,9 @@
+[project]
+name = "uv-runtime-txt"
+version = "0.0.0"
+# The Python version here intentionally:
+# - Doesn't match the version in runtime.txt
+# - Matches the distro Python version in Ubuntu 24.04
+# ...so we can test both the error message and that uv doesn't fall back to system Python.
+requires-python = "==3.12.*"
+dependencies = []
diff --git a/spec/fixtures/uv_runtime_txt/runtime.txt b/spec/fixtures/uv_runtime_txt/runtime.txt
new file mode 100644
index 000000000..67ebc4e9a
--- /dev/null
+++ b/spec/fixtures/uv_runtime_txt/runtime.txt
@@ -0,0 +1 @@
+python-3.11
diff --git a/spec/fixtures/uv_runtime_txt/uv.lock b/spec/fixtures/uv_runtime_txt/uv.lock
new file mode 100644
index 000000000..8d1d51bcf
--- /dev/null
+++ b/spec/fixtures/uv_runtime_txt/uv.lock
@@ -0,0 +1,8 @@
+version = 1
+revision = 3
+requires-python = "==3.12.*"
+
+[[package]]
+name = "uv-runtime-txt"
+version = "0.0.0"
+source = { virtual = "." }
diff --git a/spec/fixtures/venv_in_app_source/.gitignore b/spec/fixtures/venv_in_app_source/.gitignore
new file mode 100644
index 000000000..04e429ac0
--- /dev/null
+++ b/spec/fixtures/venv_in_app_source/.gitignore
@@ -0,0 +1,2 @@
+# Overrides the repo root's .gitignore, which includes `.venv/`
+!*
diff --git a/spec/fixtures/venv_in_app_source/.python-version b/spec/fixtures/venv_in_app_source/.python-version
new file mode 100644
index 000000000..6324d401a
--- /dev/null
+++ b/spec/fixtures/venv_in_app_source/.python-version
@@ -0,0 +1 @@
+3.14
diff --git a/spec/fixtures/venv_in_app_source/.venv/bin/python b/spec/fixtures/venv_in_app_source/.venv/bin/python
new file mode 100644
index 000000000..03879ebe8
--- /dev/null
+++ b/spec/fixtures/venv_in_app_source/.venv/bin/python
@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+# This file emulates a Python venv having been committed to the app's Git repo.
+
+set -euo pipefail
+
+exit 0
diff --git a/spec/fixtures/venv_in_app_source/.venv/pyvenv.cfg b/spec/fixtures/venv_in_app_source/.venv/pyvenv.cfg
new file mode 100644
index 000000000..2cefa6c36
--- /dev/null
+++ b/spec/fixtures/venv_in_app_source/.venv/pyvenv.cfg
@@ -0,0 +1 @@
+# This file emulates a Python venv having been committed to the app's Git repo.
diff --git a/spec/fixtures/venv_in_app_source/requirements.txt b/spec/fixtures/venv_in_app_source/requirements.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/spec/hatchet/checks_spec.rb b/spec/hatchet/checks_spec.rb
new file mode 100644
index 000000000..bf8bbdc17
--- /dev/null
+++ b/spec/hatchet/checks_spec.rb
@@ -0,0 +1,124 @@
+# frozen_string_literal: true
+
+require_relative '../spec_helper'
+
+RSpec.describe 'Buildpack validation checks' do
+  context 'when there are duplicate Python buildpacks set on the app' do
+    let(:buildpacks) { %i[default default] }
+    let(:app) { Hatchet::Runner.new('spec/fixtures/python_version_unspecified', buildpacks:, allow_failure: true) }
+
+    it 'fails the build with an informative error message' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Python app detected
+          remote: 
+          remote:  !     Error: The Python buildpack has already been run this build.
+          remote:  !     
+          remote:  !     An existing Python installation was found in the build directory
+          remote:  !     from a buildpack run earlier in the build.
+          remote:  !     
+          remote:  !     This normally means there are duplicate Python buildpacks set
+          remote:  !     on your app, which isn't supported, can cause errors and
+          remote:  !     slow down builds.
+          remote:  !     
+          remote:  !     Check the buildpacks set on your app and remove any duplicate
+          remote:  !     Python buildpack entries:
+          remote:  !     https://devcenter.heroku.com/articles/managing-buildpacks#view-your-buildpacks
+          remote:  !     https://devcenter.heroku.com/articles/managing-buildpacks#remove-classic-buildpacks
+          remote:  !     
+          remote:  !     Note: This error replaces the deprecation warning which was
+          remote:  !     displayed in build logs starting 13th December 2024.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        OUTPUT
+      end
+    end
+  end
+
+  context 'when the app source contains a broken Python install' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/python_in_app_source', allow_failure: true) }
+
+    it 'fails the build with an informative error message' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Python app detected
+          remote: 
+          remote:  !     Error: Existing '.heroku/python/' directory found.
+          remote:  !     
+          remote:  !     Your app's source code contains an existing directory named
+          remote:  !     '.heroku/python/', which is where the Python buildpack needs
+          remote:  !     to install its files. This existing directory contains:
+          remote:  !     
+          remote:  !     .heroku/python/
+          remote:  !     .heroku/python/bin
+          remote:  !     .heroku/python/bin/python
+          remote:  !     
+          remote:  !     Writing to internal locations used by the Python buildpack
+          remote:  !     isn't supported and can cause unexpected errors.
+          remote:  !     
+          remote:  !     If you have committed a '.heroku/python/' directory to your
+          remote:  !     Git repo, you must delete it or use a different location.
+          remote:  !     
+          remote:  !     Otherwise, check that an earlier buildpack or 'bin/pre_compile'
+          remote:  !     hook hasn't created this directory.
+          remote:  !     
+          remote:  !     Note: This error replaces the deprecation warning which was
+          remote:  !     displayed in build logs starting 13th December 2024.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        OUTPUT
+      end
+    end
+  end
+
+  context 'when the app source contains a venv directory' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/venv_in_app_source', allow_failure: true) }
+
+    it 'fails the build with an informative error message' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Python app detected
+          remote: 
+          remote:  !     Error: Existing '.venv/' directory found.
+          remote:  !     
+          remote:  !     Your app's source code contains an existing directory named
+          remote:  !     '.venv/', which looks like a Python virtual environment:
+          remote:  !     
+          remote:  !     .venv/
+          remote:  !     .venv/bin
+          remote:  !     .venv/bin/python
+          remote:  !     .venv/pyvenv.cfg
+          remote:  !     
+          remote:  !     Including a virtual environment directory in your app source
+          remote:  !     isn't supported since the files within it are specific to a
+          remote:  !     single machine and so won't work when run somewhere else.
+          remote:  !     
+          remote:  !     If you've committed a '.venv/' directory to your Git repo, you
+          remote:  !     must delete it and add the directory to your .gitignore file.
+          remote:  !     
+          remote:  !     To do this:
+          remote:  !     1. Run 'git rm --cached -r .venv/' to remove the directory
+          remote:  !        from the Git index.
+          remote:  !     2. Create a '.gitignore' file in the root of your repository
+          remote:  !        if it doesn't already exist.
+          remote:  !     3. Add the '.venv/' directory to the .gitignore file as a
+          remote:  !        new entry on its own line (don't include the quotes).
+          remote:  !     4. Stage the change using 'git add .gitignore' and then
+          remote:  !        'git commit' all changes.
+          remote:  !     
+          remote:  !     For more information, see:
+          remote:  !     https://docs.github.com/en/get-started/git-basics/ignoring-files
+          remote:  !     
+          remote:  !     If the directory was created by a 'bin/pre_compile' hook or
+          remote:  !     an earlier buildpack, you must instead update them to create
+          remote:  !     the virtual environment in a different location.
+          remote:  !     
+          remote:  !     Note: This error replaces the previous warning which had been
+          remote:  !     displayed in build logs since 2nd September 2025.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        OUTPUT
+      end
+    end
+  end
+end
diff --git a/spec/hatchet/ci_spec.rb b/spec/hatchet/ci_spec.rb
index eb0b2c5db..9b4ba8af9 100644
--- a/spec/hatchet/ci_spec.rb
+++ b/spec/hatchet/ci_spec.rb
@@ -3,46 +3,372 @@
 require_relative '../spec_helper'
 
 RSpec.describe 'Heroku CI' do
-  it 'installs both normal and test dependencies and uses cache on subsequent runs' do
-    Hatchet::Runner.new('spec/fixtures/ci_requirements', allow_failure: true).run_ci do |test_run|
-      expect(test_run.output).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
-        -----> Python app detected
-        -----> No Python version was specified. Using the buildpack default: python-#{DEFAULT_PYTHON_VERSION}
-               To use a different version, see: https://devcenter.heroku.com/articles/python-runtimes
-        -----> Installing python-#{DEFAULT_PYTHON_VERSION}
-        -----> Installing pip #{PIP_VERSION}, setuptools #{SETUPTOOLS_VERSION} and wheel #{WHEEL_VERSION}
-        -----> Installing SQLite3
-        -----> Installing requirements with pip
-               .*
-               Successfully installed urllib3-.*
-        -----> Installing test dependencies...
-               .*
-               Successfully installed .* pytest-.*
-        -----> Skipping Django collectstatic since the env var DISABLE_COLLECTSTATIC is set.
-        -----> No test-setup command provided. Skipping.
-        -----> Running test command `pytest --version`...
-        pytest .*
-        -----> test command `pytest --version` completed successfully
-      REGEX
-
-      test_run.run_again
-
-      expect(test_run.output).to match(Regexp.new(<<~REGEX))
-        -----> Python app detected
-        -----> No Python version was specified. Using the same version as the last build: python-#{DEFAULT_PYTHON_VERSION}
-               To use a different version, see: https://devcenter.heroku.com/articles/python-runtimes
-        -----> No change in requirements detected, installing from cache
-        -----> Using cached install of python-#{DEFAULT_PYTHON_VERSION}
-        -----> Installing pip #{PIP_VERSION}, setuptools #{SETUPTOOLS_VERSION} and wheel #{WHEEL_VERSION}
-        -----> Installing SQLite3
-        -----> Installing requirements with pip
-        -----> Installing test dependencies...
-        -----> Skipping Django collectstatic since the env var DISABLE_COLLECTSTATIC is set.
-        -----> No test-setup command provided. Skipping.
-        -----> Running test command `pytest --version`...
-        pytest .*
-        -----> test command `pytest --version` completed successfully
-      REGEX
+  let(:buildpacks) { [:default, 'heroku-community/inline'] }
+
+  context 'when using pip' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/ci_pip', buildpacks:) }
+
+    it 'installs both normal and test dependencies and uses cache on subsequent runs' do
+      app.run_ci do |test_run|
+        expect(clean_output(test_run.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
+          -----> Python app detected
+          -----> Using Python #{DEFAULT_PYTHON_MAJOR_VERSION} specified in .python-version
+          -----> Installing Python #{DEFAULT_PYTHON_FULL_VERSION}
+          -----> Installing pip #{PIP_VERSION}
+          -----> Installing dependencies using 'pip install -r requirements.txt -r requirements-test.txt'
+                 .+
+                 Successfully installed .+ pytest-.+ typing-extensions-.+
+          -----> Skipping Django collectstatic since the env var DISABLE_COLLECTSTATIC is set.
+          -----> Running bin/post_compile hook
+                 BUILD_DIR=/app
+                 CACHE_DIR=/tmp/cache.+
+                 CI=true
+                 CPLUS_INCLUDE_PATH=/app/.heroku/python/include
+                 C_INCLUDE_PATH=/app/.heroku/python/include
+                 DISABLE_COLLECTSTATIC=1
+                 ENV_DIR=/tmp/env.+
+                 INSTALL_TEST=1
+                 LANG=en_US.UTF-8
+                 LC_ALL=C.UTF-8
+                 LD_LIBRARY_PATH=/app/.heroku/python/lib
+                 LIBRARY_PATH=/app/.heroku/python/lib
+                 PATH=/app/.heroku/python/bin:/usr/local/bin:/usr/bin:/bin:/app/.sprettur/bin/
+                 PIP_DISABLE_PIP_VERSION_CHECK=1
+                 PKG_CONFIG_PATH=/app/.heroku/python/lib/pkg-config
+                 PYTHONUNBUFFERED=1
+          -----> Saving cache
+
+           !     Note: We recently added support for the package manager uv:
+           !     https://devcenter.heroku.com/changelog-items/3238
+           !     
+           !     It's now our recommended Python package manager, since it
+           !     supports lockfiles, is faster, gives more helpful error
+           !     messages, and is actively maintained by a full-time team.
+           !     
+           !     If you haven't tried it yet, we suggest you take a look!
+           !     https://docs.astral.sh/uv/
+
+          -----> Inline app detected
+          LANG=en_US.UTF-8
+          LD_LIBRARY_PATH=/app/.heroku/python/lib
+          LIBRARY_PATH=/app/.heroku/python/lib
+          PATH=/app/.heroku/python/bin:/usr/local/bin:/usr/bin:/bin:/app/.sprettur/bin/
+          PIP_DISABLE_PIP_VERSION_CHECK=1
+          PYTHONHOME=/app/.heroku/python
+          PYTHONPATH=/app
+          PYTHONUNBUFFERED=true
+          -----> No test-setup command provided. Skipping.
+          -----> Running test command `./bin/print-env-vars.sh && pytest --version`...
+          CI=true
+          DYNO_RAM=2560
+          FORWARDED_ALLOW_IPS=\\*
+          GUNICORN_CMD_ARGS=--access-logfile -
+          LANG=en_US.UTF-8
+          LD_LIBRARY_PATH=/app/.heroku/python/lib
+          LIBRARY_PATH=/app/.heroku/python/lib
+          PATH=/app/.heroku/python/bin:/usr/local/bin:/usr/bin:/bin:/app/.sprettur/bin/:/app/.sprettur/bin/
+          PIP_DISABLE_PIP_VERSION_CHECK=1
+          PYTHONHOME=/app/.heroku/python
+          PYTHONPATH=/app
+          PYTHONUNBUFFERED=true
+          WEB_CONCURRENCY=5
+          WEB_CONCURRENCY_SET_BY=heroku/python
+          pytest .+
+          -----> test command `./bin/print-env-vars.sh && pytest --version` completed successfully
+        REGEX
+
+        test_run.run_again
+        expect(clean_output(test_run.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
+          -----> Python app detected
+          -----> Using Python #{DEFAULT_PYTHON_MAJOR_VERSION} specified in .python-version
+          -----> Restoring cache
+          -----> Using cached install of Python #{DEFAULT_PYTHON_FULL_VERSION}
+          -----> Installing pip #{PIP_VERSION}
+          -----> Installing dependencies using 'pip install -r requirements.txt -r requirements-test.txt'
+                 Requirement already satisfied: typing-extensions==.+
+                 Requirement already satisfied: pytest==.+
+                 .+
+          -----> Skipping Django collectstatic since the env var DISABLE_COLLECTSTATIC is set.
+          -----> Running bin/post_compile hook
+        REGEX
+      end
+    end
+  end
+
+  context 'when using Pipenv' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/ci_pipenv', buildpacks:) }
+
+    it 'installs both normal and test dependencies and uses cache on subsequent runs' do
+      app.run_ci do |test_run|
+        expect(clean_output(test_run.output)).to match(Regexp.new(<<~REGEX))
+          -----> Python app detected
+          -----> Using Python #{DEFAULT_PYTHON_MAJOR_VERSION} specified in .python-version
+          -----> Installing Python #{DEFAULT_PYTHON_FULL_VERSION}
+          -----> Installing Pipenv #{PIPENV_VERSION}
+          -----> Installing dependencies using 'pipenv install --deploy --dev'
+          -----> Skipping Django collectstatic since the env var DISABLE_COLLECTSTATIC is set.
+          -----> Running bin/post_compile hook
+                 BUILD_DIR=/app
+                 CACHE_DIR=/tmp/cache.+
+                 CI=true
+                 CPLUS_INCLUDE_PATH=/app/.heroku/python/include
+                 C_INCLUDE_PATH=/app/.heroku/python/include
+                 DISABLE_COLLECTSTATIC=1
+                 ENV_DIR=/tmp/env.+
+                 INSTALL_TEST=1
+                 LANG=en_US.UTF-8
+                 LC_ALL=C.UTF-8
+                 LD_LIBRARY_PATH=/app/.heroku/python/lib
+                 LIBRARY_PATH=/app/.heroku/python/lib
+                 PATH=/app/.heroku/python/pipenv/bin:/app/.heroku/python/bin:/usr/local/bin:/usr/bin:/bin:/app/.sprettur/bin/
+                 PIPENV_SYSTEM=1
+                 PIPENV_VERBOSITY=-1
+                 PKG_CONFIG_PATH=/app/.heroku/python/lib/pkg-config
+                 PYTHONUNBUFFERED=1
+                 VIRTUAL_ENV=/app/.heroku/python
+          -----> Saving cache
+
+           !     Note: We recently added support for the package manager uv:
+           !     https://devcenter.heroku.com/changelog-items/3238
+           !     
+           !     It's now our recommended Python package manager, since it
+           !     supports lockfiles, is faster, gives more helpful error
+           !     messages, and is actively maintained by a full-time team.
+           !     
+           !     If you haven't tried it yet, we suggest you take a look!
+           !     https://docs.astral.sh/uv/
+
+          -----> Inline app detected
+          LANG=en_US.UTF-8
+          LD_LIBRARY_PATH=/app/.heroku/python/lib
+          LIBRARY_PATH=/app/.heroku/python/lib
+          PATH=/app/.heroku/python/bin:/app/.heroku/python/pipenv/bin:/usr/local/bin:/usr/bin:/bin:/app/.sprettur/bin/
+          PIPENV_SYSTEM=1
+          PIPENV_VERBOSITY=-1
+          PYTHONHOME=/app/.heroku/python
+          PYTHONPATH=/app
+          PYTHONUNBUFFERED=true
+          VIRTUAL_ENV=/app/.heroku/python
+          -----> No test-setup command provided. Skipping.
+          -----> Running test command `./bin/print-env-vars.sh && pytest --version`...
+          CI=true
+          DYNO_RAM=2560
+          FORWARDED_ALLOW_IPS=\\*
+          GUNICORN_CMD_ARGS=--access-logfile -
+          LANG=en_US.UTF-8
+          LD_LIBRARY_PATH=/app/.heroku/python/lib
+          LIBRARY_PATH=/app/.heroku/python/lib
+          PATH=/app/.heroku/python/bin:/app/.heroku/python/pipenv/bin:/usr/local/bin:/usr/bin:/bin:/app/.sprettur/bin/:/app/.sprettur/bin/
+          PIPENV_SYSTEM=1
+          PIPENV_VERBOSITY=-1
+          PYTHONHOME=/app/.heroku/python
+          PYTHONPATH=/app
+          PYTHONUNBUFFERED=true
+          VIRTUAL_ENV=/app/.heroku/python
+          WEB_CONCURRENCY=5
+          WEB_CONCURRENCY_SET_BY=heroku/python
+          pytest .+
+          -----> test command `./bin/print-env-vars.sh && pytest --version` completed successfully
+        REGEX
+
+        test_run.run_again
+        expect(clean_output(test_run.output)).to match(Regexp.new(<<~REGEX))
+          -----> Python app detected
+          -----> Using Python #{DEFAULT_PYTHON_MAJOR_VERSION} specified in .python-version
+          -----> Restoring cache
+          -----> Using cached install of Python #{DEFAULT_PYTHON_FULL_VERSION}
+          -----> Using cached Pipenv #{PIPENV_VERSION}
+          -----> Installing dependencies using 'pipenv install --deploy --dev'
+          -----> Skipping Django collectstatic since the env var DISABLE_COLLECTSTATIC is set.
+          -----> Running bin/post_compile hook
+        REGEX
+      end
+    end
+  end
+
+  context 'when using Poetry' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/ci_poetry', buildpacks:) }
+
+    it 'installs both normal and test dependencies and uses cache on subsequent runs' do
+      app.run_ci do |test_run|
+        # The Poetry install log output order is non-deterministic, hence the regex.
+        expect(clean_output(test_run.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
+          -----> Python app detected
+          -----> Using Python #{DEFAULT_PYTHON_MAJOR_VERSION} specified in .python-version
+          -----> Installing Python #{DEFAULT_PYTHON_FULL_VERSION}
+          -----> Installing Poetry #{POETRY_VERSION}
+          -----> Installing dependencies using 'poetry sync'
+                 Installing dependencies from lock file
+                 
+                 Package operations: 6 installs, 0 updates, 0 removals
+                 
+                   .+
+                   - Installing (pytest|typing-extensions) .+
+                   - Installing (pytest|typing-extensions) .+
+          -----> Skipping Django collectstatic since the env var DISABLE_COLLECTSTATIC is set.
+          -----> Running bin/post_compile hook
+                 BUILD_DIR=/app
+                 CACHE_DIR=/tmp/cache.+
+                 CI=true
+                 CPLUS_INCLUDE_PATH=/app/.heroku/python/include
+                 C_INCLUDE_PATH=/app/.heroku/python/include
+                 DISABLE_COLLECTSTATIC=1
+                 ENV_DIR=/tmp/env.+
+                 INSTALL_TEST=1
+                 LANG=en_US.UTF-8
+                 LC_ALL=C.UTF-8
+                 LD_LIBRARY_PATH=/app/.heroku/python/lib
+                 LIBRARY_PATH=/app/.heroku/python/lib
+                 PATH=/tmp/cache\\w+/.heroku/python-poetry/bin:/app/.heroku/python/bin:/usr/local/bin:/usr/bin:/bin:/app/.sprettur/bin/
+                 PKG_CONFIG_PATH=/app/.heroku/python/lib/pkg-config
+                 POETRY_VIRTUALENVS_CREATE=false
+                 POETRY_VIRTUALENVS_USE_POETRY_PYTHON=true
+                 PYTHONUNBUFFERED=1
+          -----> Saving cache
+
+           !     Note: We recently added support for the package manager uv:
+           !     https://devcenter.heroku.com/changelog-items/3238
+           !     
+           !     It's now our recommended Python package manager, since it
+           !     supports lockfiles, is faster, gives more helpful error
+           !     messages, and is actively maintained by a full-time team.
+           !     
+           !     If you haven't tried it yet, we suggest you take a look!
+           !     https://docs.astral.sh/uv/
+
+          -----> Inline app detected
+          LANG=en_US.UTF-8
+          LD_LIBRARY_PATH=/app/.heroku/python/lib
+          LIBRARY_PATH=/app/.heroku/python/lib
+          PATH=/app/.heroku/python/bin:/tmp/cache\\w+/.heroku/python-poetry/bin:/usr/local/bin:/usr/bin:/bin:/app/.sprettur/bin/
+          POETRY_VIRTUALENVS_CREATE=false
+          POETRY_VIRTUALENVS_USE_POETRY_PYTHON=true
+          PYTHONHOME=/app/.heroku/python
+          PYTHONPATH=/app
+          PYTHONUNBUFFERED=true
+          -----> No test-setup command provided. Skipping.
+          -----> Running test command `./bin/print-env-vars.sh && pytest --version`...
+          CI=true
+          DYNO_RAM=2560
+          FORWARDED_ALLOW_IPS=\\*
+          GUNICORN_CMD_ARGS=--access-logfile -
+          LANG=en_US.UTF-8
+          LD_LIBRARY_PATH=/app/.heroku/python/lib
+          LIBRARY_PATH=/app/.heroku/python/lib
+          PATH=/app/.heroku/python/bin:/usr/local/bin:/usr/bin:/bin:/app/.sprettur/bin/:/app/.sprettur/bin/
+          PYTHONHOME=/app/.heroku/python
+          PYTHONPATH=/app
+          PYTHONUNBUFFERED=true
+          WEB_CONCURRENCY=5
+          WEB_CONCURRENCY_SET_BY=heroku/python
+          pytest .+
+          -----> test command `./bin/print-env-vars.sh && pytest --version` completed successfully
+        REGEX
+
+        test_run.run_again
+        expect(clean_output(test_run.output)).to include(<<~OUTPUT)
+          -----> Python app detected
+          -----> Using Python #{DEFAULT_PYTHON_MAJOR_VERSION} specified in .python-version
+          -----> Restoring cache
+          -----> Using cached install of Python #{DEFAULT_PYTHON_FULL_VERSION}
+          -----> Installing Poetry #{POETRY_VERSION}
+          -----> Installing dependencies using 'poetry sync'
+                 Installing dependencies from lock file
+                 
+                 No dependencies to install or update
+          -----> Skipping Django collectstatic since the env var DISABLE_COLLECTSTATIC is set.
+          -----> Running bin/post_compile hook
+        OUTPUT
+      end
+    end
+  end
+
+  context 'when using uv' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/ci_uv', buildpacks:) }
+
+    it 'installs both normal and test dependencies and uses cache on subsequent runs' do
+      app.run_ci do |test_run|
+        # The uv install log output order is non-deterministic, hence the regex.
+        expect(clean_output(test_run.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
+          -----> Python app detected
+          -----> Using Python #{DEFAULT_PYTHON_MAJOR_VERSION} specified in .python-version
+          -----> Installing Python #{DEFAULT_PYTHON_FULL_VERSION}
+          -----> Installing uv #{UV_VERSION}
+          -----> Installing dependencies using 'uv sync --locked'
+                 Resolved 8 packages in .+s
+                 Prepared 6 packages in .+s
+                 Installed 6 packages in .+s
+                 Bytecode compiled .+ files in .+s
+                  .+
+                  \\+ (pytest|typing-extensions)==.+
+                  \\+ (pytest|typing-extensions)==.+
+          -----> Skipping Django collectstatic since the env var DISABLE_COLLECTSTATIC is set.
+          -----> Running bin/post_compile hook
+                 BUILD_DIR=/app
+                 CACHE_DIR=/tmp/cache.+
+                 CI=true
+                 CPLUS_INCLUDE_PATH=/app/.heroku/python/include
+                 C_INCLUDE_PATH=/app/.heroku/python/include
+                 DISABLE_COLLECTSTATIC=1
+                 ENV_DIR=/tmp/env.+
+                 INSTALL_TEST=1
+                 LANG=en_US.UTF-8
+                 LC_ALL=C.UTF-8
+                 LD_LIBRARY_PATH=/app/.heroku/python/lib
+                 LIBRARY_PATH=/app/.heroku/python/lib
+                 PATH=/tmp/cache\\w+/.heroku/python-uv:/app/.heroku/python/bin:/usr/local/bin:/usr/bin:/bin:/app/.sprettur/bin/
+                 PKG_CONFIG_PATH=/app/.heroku/python/lib/pkg-config
+                 PYTHONUNBUFFERED=1
+                 UV_LINK_MODE=hardlink
+                 UV_NO_MANAGED_PYTHON=1
+                 UV_PROJECT_ENVIRONMENT=/app/.heroku/python
+                 UV_PYTHON_DOWNLOADS=never
+          -----> Saving cache
+          -----> Inline app detected
+          LANG=en_US.UTF-8
+          LD_LIBRARY_PATH=/app/.heroku/python/lib
+          LIBRARY_PATH=/app/.heroku/python/lib
+          PATH=/app/.heroku/python/bin:/tmp/cache\\w+/.heroku/python-uv:/usr/local/bin:/usr/bin:/bin:/app/.sprettur/bin/
+          PYTHONHOME=/app/.heroku/python
+          PYTHONPATH=/app
+          PYTHONUNBUFFERED=true
+          UV_LINK_MODE=hardlink
+          UV_NO_MANAGED_PYTHON=1
+          UV_PROJECT_ENVIRONMENT=/app/.heroku/python
+          UV_PYTHON_DOWNLOADS=never
+          -----> No test-setup command provided. Skipping.
+          -----> Running test command `./bin/print-env-vars.sh && pytest --version`...
+          CI=true
+          DYNO_RAM=2560
+          FORWARDED_ALLOW_IPS=\\*
+          GUNICORN_CMD_ARGS=--access-logfile -
+          LANG=en_US.UTF-8
+          LD_LIBRARY_PATH=/app/.heroku/python/lib
+          LIBRARY_PATH=/app/.heroku/python/lib
+          PATH=/app/.heroku/python/bin:/usr/local/bin:/usr/bin:/bin:/app/.sprettur/bin/:/app/.sprettur/bin/
+          PYTHONHOME=/app/.heroku/python
+          PYTHONPATH=/app
+          PYTHONUNBUFFERED=true
+          WEB_CONCURRENCY=5
+          WEB_CONCURRENCY_SET_BY=heroku/python
+          pytest .+
+          -----> test command `./bin/print-env-vars.sh && pytest --version` completed successfully
+        REGEX
+
+        test_run.run_again
+        expect(clean_output(test_run.output)).to match(Regexp.new(<<~REGEX))
+          -----> Python app detected
+          -----> Using Python #{DEFAULT_PYTHON_MAJOR_VERSION} specified in .python-version
+          -----> Restoring cache
+          -----> Using cached install of Python #{DEFAULT_PYTHON_FULL_VERSION}
+          -----> Using cached uv #{UV_VERSION}
+          -----> Installing dependencies using 'uv sync --locked'
+                 Resolved 8 packages in .+s
+                 Bytecode compiled .+ files in .+s
+          -----> Skipping Django collectstatic since the env var DISABLE_COLLECTSTATIC is set.
+          -----> Running bin/post_compile hook
+        REGEX
+      end
     end
   end
 end
diff --git a/spec/hatchet/detect_spec.rb b/spec/hatchet/detect_spec.rb
index ceb25581f..4a93262ee 100644
--- a/spec/hatchet/detect_spec.rb
+++ b/spec/hatchet/detect_spec.rb
@@ -17,12 +17,13 @@
           remote:  !     Error: Your app is configured to use the Python buildpack,
           remote:  !     but we couldn't find any supported Python project files.
           remote:  !     
-          remote:  !     A Python app on Heroku must have either a 'requirements.txt' or
-          remote:  !     'Pipfile' package manager file in the root directory of its
-          remote:  !     source code.
+          remote:  !     A Python app on Heroku must have either a 'requirements.txt',
+          remote:  !     'Pipfile.lock', 'poetry.lock' or 'uv.lock' package manager file
+          remote:  !     in the root directory of its source code.
           remote:  !     
           remote:  !     Currently the root directory of your app contains:
           remote:  !     
+          remote:  !     .example-dotfile
           remote:  !     README.md
           remote:  !     subdir/
           remote:  !     
@@ -31,15 +32,23 @@
           remote:  !     1. Is in the top level directory (not a subdirectory).
           remote:  !     2. Has the correct spelling (the filenames are case-sensitive).
           remote:  !     3. Isn't listed in '.gitignore' or '.slugignore'.
+          remote:  !     4. Has been added to the Git repository using 'git add --all'
+          remote:  !        and then committed using 'git commit'.
           remote:  !     
           remote:  !     Otherwise, add a package manager file to your app. If your app has
           remote:  !     no dependencies, then create an empty 'requirements.txt' file.
           remote:  !     
+          remote:  !     If you aren't sure which package manager to use, we recommend
+          remote:  !     trying uv, since it supports lockfiles, is extremely fast, and
+          remote:  !     is actively maintained by a full-time team:
+          remote:  !     https://docs.astral.sh/uv/
+          remote:  !     
           remote:  !     For help with using Python on Heroku, see:
           remote:  !     https://devcenter.heroku.com/articles/getting-started-with-python
           remote:  !     https://devcenter.heroku.com/articles/python-support
           remote: 
-          remote:        More info: https://devcenter.heroku.com/articles/buildpacks#detection-failure
+          remote: 
+          remote:        More info: https://devcenter.heroku.com/articles/buildpacks#buildpack-auto-detection
         OUTPUT
       end
     end
diff --git a/spec/hatchet/django_spec.rb b/spec/hatchet/django_spec.rb
index 865d5b833..664410dd7 100644
--- a/spec/hatchet/django_spec.rb
+++ b/spec/hatchet/django_spec.rb
@@ -4,105 +4,257 @@
 
 # Tests that broken user-provided env vars don't take precedence over those set by this buildpack
 # and break running Python. This is particularly important when using shared builds of Python,
-# since they rely upon `LD_LIBRARY_PATH` being correct. This list of env vars is based on those
-# that used to be set to different values by `bin/release` in very old versions of the buildpack:
+# since they rely upon `LD_LIBRARY_PATH` being correct. Some of these are based on the env vars
+# that used to be set by `bin/release` by very old versions of the buildpack:
 # https://github.com/heroku/heroku-buildpack-python/blob/27abdfe7d7ad104dabceb45641415251e965671c/bin/release#L11-L18
 BROKEN_CONFIG_VARS = {
+  BUILD_DIR: '/invalid-path',
+  C_INCLUDE_PATH: '/invalid-path',
+  CACHE_DIR: '/invalid-path',
+  CPLUS_INCLUDE_PATH: '/invalid-path',
+  ENV_DIR: '/invalid-path',
   LD_LIBRARY_PATH: '/invalid-path',
   LIBRARY_PATH: '/invalid-path',
   PATH: '/invalid-path',
+  PKG_CONFIG_PATH: '/invalid-path',
   PYTHONHOME: '/invalid-path',
   PYTHONPATH: '/invalid-path',
 }.freeze
 
 RSpec.describe 'Django support' do
-  describe 'collectstatic' do
-    context 'when building a Django project' do
-      let(:app) { Hatchet::Runner.new('python-getting-started', config: BROKEN_CONFIG_VARS) }
-
-      it 'runs collectstatic' do
-        app.deploy do |app|
-          expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
-            remote: -----> \\$ python manage.py collectstatic --noinput
-            remote:        WARNING:root:No DATABASE_URL environment variable set, and so no databases setup
-            remote:        \\d+ static files? copied to '/tmp/build_.*/staticfiles', \\d+ post-processed.
-          REGEX
-        end
+  context 'when building latest Django with the app nested inside a subfolder' do
+    # Also tests that app config vars are passed to the 'manage.py' script invocations.
+    let(:config) { { EXPECTED_ENV_VAR: '1' } }
+    let(:app) { Hatchet::Runner.new('spec/fixtures/django_staticfiles_latest_django', config:) }
+
+    it 'runs collectstatic' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
+          remote:        Successfully installed Django-.+
+          remote: -----> \\$ python backend/manage.py collectstatic --noinput
+          remote:        \\{'BUILD_DIR': '/tmp/build_\\w+',
+          remote:         'CACHE_DIR': '/tmp/codon/tmp/cache',
+          remote:         'CPLUS_INCLUDE_PATH': '/app/.heroku/python/include',
+          remote:         'C_INCLUDE_PATH': '/app/.heroku/python/include',
+          remote:         'DJANGO_SETTINGS_MODULE': 'testproject.settings',
+          remote:         'ENV_DIR': '/tmp/.+',
+          remote:         'EXPECTED_ENV_VAR': '1',
+          remote:         'LANG': 'en_US.UTF-8',
+          remote:         'LD_LIBRARY_PATH': '/app/.heroku/python/lib',
+          remote:         'LIBRARY_PATH': '/app/.heroku/python/lib',
+          remote:         'PATH': '/app/.heroku/python/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin',
+          remote:         'PIP_DISABLE_PIP_VERSION_CHECK': '1',
+          remote:         'PKG_CONFIG_PATH': '/app/.heroku/python/lib/pkg-config',
+          remote:         'PWD': '/tmp/build_\\w+',
+          remote:         'PYTHONPATH': '\\.',
+          remote:         'PYTHONUNBUFFERED': '1'\\}
+          remote:        
+          remote:        \\['/tmp/build_\\w+/backend',
+          remote:         '/tmp/build_\\w+',
+          remote:         '/app/.heroku/python/lib/python314.zip',
+          remote:         '/app/.heroku/python/lib/python3.14',
+          remote:         '/app/.heroku/python/lib/python3.14/lib-dynload',
+          remote:         '/app/.heroku/python/lib/python3.14/site-packages'\\]
+          remote:        
+          remote:        1 static file copied to '/tmp/build_\\w+/backend/staticfiles'.
+          remote: 
+          remote: -----> Saving cache
+        REGEX
       end
     end
+  end
 
-    context 'when Django is installed but manage.py does not exist' do
-      let(:app) { Hatchet::Runner.new('spec/fixtures/requirements_django_latest') }
+  context 'when building legacy Django with broken env vars set' do
+    # Also tests that app config vars are passed to the 'manage.py' script invocations.
+    let(:config) { BROKEN_CONFIG_VARS.merge(EXPECTED_ENV_VAR: '1') }
+    let(:app) { Hatchet::Runner.new('spec/fixtures/django_staticfiles_legacy_django', config:) }
 
-      it 'skips collectstatic' do
-        app.deploy do |app|
-          expect(app.output).to include('Skipping Django collectstatic since no manage.py file found.')
-          expect(app.output).not_to include('manage.py collectstatic')
-        end
+    it 'runs collectstatic' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
+          remote:        Successfully installed Django-.+
+          remote: -----> \\$ python manage.py collectstatic --noinput
+          remote:        \\{'BUILD_DIR': '/invalid-path',
+          remote:         'CACHE_DIR': '/invalid-path',
+          remote:         'CPLUS_INCLUDE_PATH': '/invalid-path',
+          remote:         'C_INCLUDE_PATH': '/invalid-path',
+          remote:         'DJANGO_SETTINGS_MODULE': 'testproject.settings',
+          remote:         'ENV_DIR': '/invalid-path',
+          remote:         'EXPECTED_ENV_VAR': '1',
+          remote:         'LANG': 'en_US.UTF-8',
+          remote:         'LD_LIBRARY_PATH': '/app/.heroku/python/lib',
+          remote:         'LIBRARY_PATH': '/app/.heroku/python/lib',
+          remote:         'PATH': '/app/.heroku/python/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin',
+          remote:         'PIP_DISABLE_PIP_VERSION_CHECK': '1',
+          remote:         'PKG_CONFIG_PATH': '/invalid-path',
+          remote:         'PWD': '/tmp/build_\\w+',
+          remote:         'PYTHONPATH': '/invalid-path',
+          remote:         'PYTHONUNBUFFERED': '1'\\}
+          remote:        
+          remote:        \\['/tmp/build_\\w+',
+          remote:         '/invalid-path',
+          remote:         '/app/.heroku/python/lib/python310.zip',
+          remote:         '/app/.heroku/python/lib/python3.10',
+          remote:         '/app/.heroku/python/lib/python3.10/lib-dynload',
+          remote:         '/app/.heroku/python/lib/python3.10/site-packages'\\]
+          remote:        
+          remote:        1 static file copied to '/tmp/build_\\w+/staticfiles'.
+          remote: 
+          remote: -----> Saving cache
+        REGEX
       end
     end
+  end
+
+  context 'when Django is installed but manage.py does not exist' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/django_no_manage_py') }
 
-    context 'when DISABLE_COLLECTSTATIC=1' do
-      let(:app) do
-        Hatchet::Runner.new('spec/fixtures/requirements_django_latest', config: { 'DISABLE_COLLECTSTATIC' => '1' })
+    it 'skips collectstatic' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
+          remote:        Successfully installed Django-.+
+          remote: -----> Skipping Django collectstatic since no manage.py file found.
+          remote: -----> Saving cache
+        REGEX
       end
+    end
+  end
+
+  context 'when DISABLE_COLLECTSTATIC=1' do
+    let(:config) { { DISABLE_COLLECTSTATIC: '1' } }
+    let(:app) { Hatchet::Runner.new('spec/fixtures/django_invalid_settings_module', config:) }
 
-      it 'skips collectstatic' do
-        app.deploy do |app|
-          expect(app.output).to include('Skipping Django collectstatic since the env var DISABLE_COLLECTSTATIC is set.')
-          expect(app.output).not_to include('manage.py collectstatic')
-        end
+    it 'skips collectstatic' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
+          remote:        Successfully installed Django-.+
+          remote: -----> Skipping Django collectstatic since the env var DISABLE_COLLECTSTATIC is set.
+          remote: -----> Saving cache
+        REGEX
       end
     end
+  end
 
-    context 'when DISABLE_COLLECTSTATIC=0' do
-      let(:app) { Hatchet::Runner.new('python-getting-started', config: { 'DISABLE_COLLECTSTATIC' => '0' }) }
+  context 'when .heroku/collectstatic_disabled exists' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/django_collectstatic_disabled_file') }
 
-      it 'still runs collectstatic' do
-        app.deploy do |app|
-          expect(app.output).to include('manage.py collectstatic')
-        end
+    it 'skips collectstatic with a deprecation warning' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
+          remote:        Successfully installed Django-.+
+          remote: -----> Skipping Django collectstatic since the file '.heroku/collectstatic_disabled' exists.
+          remote: 
+          remote:  !     Warning: The .heroku/collectstatic_disabled file is deprecated.
+          remote:  !     
+          remote:  !     Please remove the file and set the env var DISABLE_COLLECTSTATIC=1 instead.
+          remote: 
+          remote: -----> Saving cache
+        REGEX
       end
     end
+  end
 
-    context 'when DISABLE_COLLECTSTATIC is null' do
-      let(:app) { Hatchet::Runner.new('python-getting-started', config: { 'DISABLE_COLLECTSTATIC' => '' }) }
+  # TODO: Backport the Python CNB implementation that allows skipping collectstatic automatically for this case.
+  context 'when Django and manage.py exist but the Django staticfiles app is not enabled' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/django_staticfiles_app_not_enabled', allow_failure: true) }
 
-      it 'still runs collectstatic' do
-        app.deploy do |app|
-          expect(app.output).to include('manage.py collectstatic')
-        end
+    it 'fails collectstatic' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
+          remote:        Successfully installed Django-.+
+          remote: -----> \\$ python manage.py collectstatic --noinput
+          remote:        Unknown command: 'collectstatic'
+          remote:        Type 'manage.py help' for usage.
+          remote: 
+          remote: 
+          remote:  !     Error: Unable to generate Django static files.
+          remote:  !     
+          remote:  !     The 'python manage.py collectstatic --noinput' Django
+          remote:  !     management command to generate static files failed.
+          remote:  !     
+          remote:  !     See the traceback above for details.
+          remote:  !     
+          remote:  !     You may need to update application code to resolve this error.
+          remote:  !     Or, you can disable collectstatic for this application:
+          remote:  !     
+          remote:  !        \\$ heroku config:set DISABLE_COLLECTSTATIC=1
+          remote:  !     
+          remote:  !     https://devcenter.heroku.com/articles/django-assets
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        REGEX
       end
     end
+  end
 
-    context 'when .heroku/collectstatic_disabled exists' do
-      let(:app) { Hatchet::Runner.new('spec/fixtures/django_collectstatic_disabled_file') }
-
-      it 'skips collectstatic with a deprecation warning' do
-        app.deploy do |app|
-          expect(clean_output(app.output)).to include(<<~OUTPUT)
-            remote: -----> Skipping Django collectstatic since the file '.heroku/collectstatic_disabled' exists.
-            remote:  !     This approach is deprecated, please set the env var DISABLE_COLLECTSTATIC=1 instead.
-          OUTPUT
-          expect(app.output).not_to include('manage.py collectstatic')
-        end
+  # For now this case produces the same error message as the one below, but once we backport the
+  # Python CNB implementation that will change, so we want a dedicated test for this case.
+  context 'when manage.py is configured with an invalid settings module' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/django_invalid_settings_module', allow_failure: true) }
+
+    it 'fails collectstatic with an informative error message' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
+          remote: -----> \\$ python manage.py collectstatic --noinput
+          remote:        Traceback \\(most recent call last\\):
+          remote:        .+
+          remote:        ModuleNotFoundError: No module named 'nonexistent-module'
+          remote: 
+          remote: 
+          remote:  !     Error: Unable to generate Django static files.
+          remote:  !     
+          remote:  !     The 'python manage.py collectstatic --noinput' Django
+          remote:  !     management command to generate static files failed.
+          remote:  !     
+          remote:  !     See the traceback above for details.
+          remote:  !     
+          remote:  !     You may need to update application code to resolve this error.
+          remote:  !     Or, you can disable collectstatic for this application:
+          remote:  !     
+          remote:  !        \\$ heroku config:set DISABLE_COLLECTSTATIC=1
+          remote:  !     
+          remote:  !     https://devcenter.heroku.com/articles/django-assets
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        REGEX
       end
     end
+  end
+
+  context 'when the staticfiles app is misconfigured and DEBUG_COLLECTSTATIC=1' do
+    let(:config) { { DEBUG_COLLECTSTATIC: '1' } }
+    let(:app) { Hatchet::Runner.new('spec/fixtures/django_staticfiles_misconfigured', config:, allow_failure: true) }
 
-    context 'when building a broken Django project' do
-      let(:app) { Hatchet::Runner.new('spec/fixtures/django_broken_project', allow_failure: true) }
-
-      it 'fails collectstatic with an informative error message' do
-        app.deploy do |app|
-          expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
-            remote: -----> \\$ python manage.py collectstatic --noinput
-            remote:        Traceback \\(most recent call last\\):
-            remote:        .*
-            remote:        ModuleNotFoundError: No module named 'gettingstarted'
-            remote: 
-            remote:  !     Error while running '\\$ python manage.py collectstatic --noinput'.
-          REGEX
-        end
+    # TODO: Sort the displayed env vars to make the order deterministic and then we can test more of the output.
+    it 'fails collectstatic with an informative error message and prints env vars' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
+          remote: -----> \\$ python manage.py collectstatic --noinput
+          remote:        Traceback \\(most recent call last\\):
+          remote:        .+
+          remote:        django.core.exceptions.ImproperlyConfigured: You're using the staticfiles app without having set the required STATIC_URL setting.
+          remote: 
+          remote: 
+          remote:  !     Error: Unable to generate Django static files.
+          remote:  !     
+          remote:  !     The 'python manage.py collectstatic --noinput' Django
+          remote:  !     management command to generate static files failed.
+          remote:  !     
+          remote:  !     See the traceback above for details.
+          remote:  !     
+          remote:  !     You may need to update application code to resolve this error.
+          remote:  !     Or, you can disable collectstatic for this application:
+          remote:  !     
+          remote:  !        \\$ heroku config:set DISABLE_COLLECTSTATIC=1
+          remote:  !     
+          remote:  !     https://devcenter.heroku.com/articles/django-assets
+          remote: 
+          remote: 
+          remote: \\*\\*\\*\\*\\*\\* Collectstatic environment variables:
+          remote: 
+          remote:        .+
+          remote:  !     Push rejected, failed to compile Python app.
+        REGEX
       end
     end
   end
diff --git a/spec/hatchet/hooks_spec.rb b/spec/hatchet/hooks_spec.rb
index dd114a76b..8cf91df8d 100644
--- a/spec/hatchet/hooks_spec.rb
+++ b/spec/hatchet/hooks_spec.rb
@@ -3,49 +3,102 @@
 require_relative '../spec_helper'
 
 RSpec.describe 'Compile hooks' do
-  context 'when an app has bin/pre_compile and bin/post_compile scripts' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/hooks', config: { 'SOME_APP_CONFIG_VAR' => '1' }) }
-
-    it 'runs the hooks with the correct environment' do
-      expected_env_vars = %w[
-        _
-        BUILD_DIR
-        BUILDPACK_LOG_FILE
-        CACHE_DIR
-        C_INCLUDE_PATH
-        CPLUS_INCLUDE_PATH
-        DYNO
-        ENV_DIR
-        HOME
-        LANG
-        LD_LIBRARY_PATH
-        LIBRARY_PATH
-        OLDPWD
-        PATH
-        PIP_NO_PYTHON_VERSION_WARNING
-        PKG_CONFIG_PATH
-        PWD
-        PYTHONUNBUFFERED
-        REQUEST_ID
-        SHLVL
-        SOME_APP_CONFIG_VAR
-        SOURCE_VERSION
-        STACK
-      ]
+  # This spec skips testing the passing post_compile hook case, since that's already tested
+  # via the package manager and CI tests.
 
+  # Tests two of the four hooks result permutations in the same test to reduce end to end time.
+  context 'when an app has a passing bin/pre_compile and a failing bin/post_compile script' do
+    let(:config) { { SOME_APP_CONFIG_VAR: '1' } }
+    let(:app) { Hatchet::Runner.new('spec/fixtures/hooks_pre_compile_pass_post_compile_fail', config:, allow_failure: true) }
+
+    it 'runs the pre_compile hook but aborts the build during the post_compile hook with a suitable error message' do
       app.deploy do |app|
-        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
+        output = clean_output(app.output)
+
+        expect(output).to match(Regexp.new(<<~REGEX))
           remote: -----> Python app detected
-          remote: -----> Running pre-compile hook
-          remote: pre_compile ran with env vars:
-          remote: #{expected_env_vars.join("\nremote: ")}
-          remote: -----> No Python version was specified. Using the buildpack default: python-#{DEFAULT_PYTHON_VERSION}
-          remote: .*
-          remote: -----> Installing requirements with pip
-          remote: -----> Running post-compile hook
-          remote: post_compile ran with env vars:
-          remote: #{expected_env_vars.join("\nremote: ")}
+          remote: -----> Running bin/pre_compile hook
+          remote:        ~ pre_compile ran with env vars:
+          remote:        BUILD_DIR=/tmp/build_.+
+          remote:        CACHE_DIR=/tmp/codon/tmp/cache
+          remote:        C_INCLUDE_PATH=/app/.heroku/python/include
+          remote:        CPLUS_INCLUDE_PATH=/app/.heroku/python/include
+          remote:        ENV_DIR=/tmp/.+
+          remote:        LANG=en_US.UTF-8
+          remote:        LD_LIBRARY_PATH=/app/.heroku/python/lib
+          remote:        LIBRARY_PATH=/app/.heroku/python/lib
+          remote:        PATH=/app/.heroku/python/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+          remote:        PKG_CONFIG_PATH=/app/.heroku/python/lib/pkg-config
+          remote:        PYTHONUNBUFFERED=1
+          remote:        SOME_APP_CONFIG_VAR=1
+          remote:        ~ pre_compile complete
         REGEX
+
+        expect(output).to include(<<~OUTPUT)
+          remote: -----> Running bin/post_compile hook
+          remote:        Some post_compile error!
+          remote: 
+          remote:  !     Error: Failed to run the bin/post_compile script.
+          remote:  !     
+          remote:  !     We found a 'bin/post_compile' script in your app source, so ran
+          remote:  !     it to allow for customisation of the build process.
+          remote:  !     
+          remote:  !     However, this script exited with a non-zero exit status.
+          remote:  !     
+          remote:  !     Fix any errors output by your script above, or remove/rename
+          remote:  !     the script to prevent it from being run during the build.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        OUTPUT
+      end
+    end
+  end
+
+  context 'when an app has a failing bin/pre_compile script' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/hooks_pre_compile_fail', allow_failure: true) }
+
+    it 'aborts the build with a suitable error message' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Running bin/pre_compile hook
+          remote:        Some pre_compile error!
+          remote: 
+          remote:  !     Error: Failed to run the bin/pre_compile script.
+          remote:  !     
+          remote:  !     We found a 'bin/pre_compile' script in your app source, so ran
+          remote:  !     it to allow for customisation of the build process.
+          remote:  !     
+          remote:  !     However, this script exited with a non-zero exit status.
+          remote:  !     
+          remote:  !     Fix any errors output by your script above, or remove/rename
+          remote:  !     the script to prevent it from being run during the build.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        OUTPUT
+      end
+    end
+  end
+
+  context 'when an app tries to delete the whole cache directory including the build data file' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/hooks_delete_cache_dir', allow_failure: true) }
+
+    it 'aborts the build with a suitable error message' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Running bin/post_compile hook
+          remote:        + rm -rf /tmp/codon/tmp/cache
+          remote: 
+          remote:  !     Error: Can't find the buildpack's build data file.
+          remote:  !     
+          remote:  !     The Python buildpack's internal build data file is missing:
+          remote:  !     /tmp/codon/tmp/cache/build-data/python.json
+          remote:  !     
+          remote:  !     This file is required for the buildpack to work correctly,
+          remote:  !     and so you must not delete it when removing files from the
+          remote:  !     build cache or /tmp directories.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        OUTPUT
       end
     end
   end
diff --git a/spec/hatchet/nltk_spec.rb b/spec/hatchet/nltk_spec.rb
index 0ed2a167f..1c5a5a59d 100644
--- a/spec/hatchet/nltk_spec.rb
+++ b/spec/hatchet/nltk_spec.rb
@@ -11,13 +11,13 @@
         expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
           remote: -----> Downloading NLTK corpora...
           remote: -----> Downloading NLTK packages: city_database stopwords
-          remote: .*: RuntimeWarning: 'nltk.downloader' found in sys.modules after import of package 'nltk', but prior to execution of 'nltk.downloader'; this may result in unpredictable behaviour
-          remote: \\[nltk_data\\] Downloading package city_database to
-          remote: \\[nltk_data\\]     /tmp/build_.*/.heroku/python/nltk_data...
-          remote: \\[nltk_data\\]   Unzipping corpora/city_database.zip.
-          remote: \\[nltk_data\\] Downloading package stopwords to
-          remote: \\[nltk_data\\]     /tmp/build_.*/.heroku/python/nltk_data...
-          remote: \\[nltk_data\\]   Unzipping corpora/stopwords.zip.
+          remote:        .*: RuntimeWarning: 'nltk.downloader' found in sys.modules after import of package 'nltk', but prior to execution of 'nltk.downloader'; this may result in unpredictable behaviour
+          remote:        \\[nltk_data\\] Downloading package city_database to
+          remote:        \\[nltk_data\\]     /tmp/build_.+/.heroku/python/nltk_data...
+          remote:        \\[nltk_data\\]   Unzipping corpora/city_database.zip.
+          remote:        \\[nltk_data\\] Downloading package stopwords to
+          remote:        \\[nltk_data\\]     /tmp/build_.+/.heroku/python/nltk_data...
+          remote:        \\[nltk_data\\]   Unzipping corpora/stopwords.zip.
         REGEX
 
         # TODO: Add a test that the downloaded corpora can be found at runtime.
@@ -32,8 +32,7 @@
       app.deploy do |app|
         expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
           remote: -----> Downloading NLTK corpora...
-          remote:  !     'nltk.txt' not found, not downloading any corpora
-          remote:  !     Learn more: https://devcenter.heroku.com/articles/python-nltk
+          remote:        'nltk.txt' not found, not downloading any corpora
         REGEX
       end
     end
@@ -44,7 +43,37 @@
 
     it 'does not try to install the specified NLTK corpora' do
       app.deploy do |app|
-        expect(app.output.downcase).not_to include('nltk')
+        expect(app.output).not_to include('NLTK')
+        expect(app.output).not_to include('nltk_data')
+      end
+    end
+  end
+
+  context 'when nltk.txt contains invalid entries' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/nltk_txt_invalid', allow_failure: true) }
+
+    it 'fails the build' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
+          remote: -----> Downloading NLTK corpora...
+          remote: -----> Downloading NLTK packages: invalid!
+          remote:        .+: RuntimeWarning: 'nltk.downloader' found in sys.modules after import of package 'nltk', but prior to execution of 'nltk.downloader'; this may result in unpredictable behaviour
+          remote:        \\[nltk_data\\] Error loading invalid!: Package 'invalid!' not found in
+          remote:        \\[nltk_data\\]     index
+          remote:        Error installing package. Retry\\? \\[n/y/e\\]
+          remote:        Traceback \\(most recent call last\\):
+          remote:        .+
+          remote:        EOFError: EOF when reading a line
+          remote: 
+          remote:  !     Error: Unable to download NLTK data.
+          remote:  !     
+          remote:  !     The 'python -m nltk.downloader' command to download NLTK
+          remote:  !     data didn't exit successfully.
+          remote:  !     
+          remote:  !     See the log output above for more information.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        REGEX
       end
     end
   end
diff --git a/spec/hatchet/package_manager_spec.rb b/spec/hatchet/package_manager_spec.rb
index 10cff59b4..02f68b990 100644
--- a/spec/hatchet/package_manager_spec.rb
+++ b/spec/hatchet/package_manager_spec.rb
@@ -4,22 +4,23 @@
 
 RSpec.describe 'Package manager support' do
   context 'when there are no supported package manager files' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/runtime_txt_only', allow_failure: true) }
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pyproject_toml_only', allow_failure: true) }
 
     it 'fails the build with an informative error message' do
       app.deploy do |app|
         expect(clean_output(app.output)).to include(<<~OUTPUT)
           remote: -----> Python app detected
-          remote:  !     
+          remote: 
           remote:  !     Error: Couldn't find any supported Python package manager files.
           remote:  !     
-          remote:  !     A Python app on Heroku must have either a 'requirements.txt' or
-          remote:  !     'Pipfile' package manager file in the root directory of its
-          remote:  !     source code.
+          remote:  !     A Python app on Heroku must have either a 'requirements.txt',
+          remote:  !     'Pipfile.lock', 'poetry.lock' or 'uv.lock' package manager file
+          remote:  !     in the root directory of its source code.
           remote:  !     
           remote:  !     Currently the root directory of your app contains:
           remote:  !     
-          remote:  !     runtime.txt
+          remote:  !     .example-dotfile
+          remote:  !     pyproject.toml
           remote:  !     subdir/
           remote:  !     
           remote:  !     If your app already has a package manager file, check that it:
@@ -27,16 +28,135 @@
           remote:  !     1. Is in the top level directory (not a subdirectory).
           remote:  !     2. Has the correct spelling (the filenames are case-sensitive).
           remote:  !     3. Isn't listed in '.gitignore' or '.slugignore'.
+          remote:  !     4. Has been added to the Git repository using 'git add --all'
+          remote:  !        and then committed using 'git commit'.
           remote:  !     
           remote:  !     Otherwise, add a package manager file to your app. If your app has
           remote:  !     no dependencies, then create an empty 'requirements.txt' file.
           remote:  !     
+          remote:  !     If you aren't sure which package manager to use, we recommend
+          remote:  !     trying uv, since it supports lockfiles, is extremely fast, and
+          remote:  !     is actively maintained by a full-time team:
+          remote:  !     https://docs.astral.sh/uv/
+          remote:  !     
           remote:  !     For help with using Python on Heroku, see:
           remote:  !     https://devcenter.heroku.com/articles/getting-started-with-python
           remote:  !     https://devcenter.heroku.com/articles/python-support
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        OUTPUT
+      end
+    end
+  end
+
+  context 'when there is only a setup.py' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/setup_py_only', allow_failure: true) }
+
+    it 'fails the build with an informative error message' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Python app detected
+          remote: 
+          remote:  !     Error: Implicit setup.py file support has been sunset.
+          remote:  !     
+          remote:  !     Your app currently only has a setup.py file and no Python
+          remote:  !     package manager files. This means that the buildpack can't
+          remote:  !     tell which package manager you want to use, and whether to
+          remote:  !     install your project in editable mode or not.
+          remote:  !     
+          remote:  !     Previously the buildpack guessed and used pip to install your
+          remote:  !     dependencies in editable mode. However, this fallback was
+          remote:  !     deprecated in September 2025 and has now been sunset.
+          remote:  !     
+          remote:  !     You must now add an explicit package manager file to your app,
+          remote:  !     such as a requirements.txt, poetry.lock or uv.lock file.
           remote:  !     
+          remote:  !     To continue using your setup.py file with pip in editable
+          remote:  !     mode, create a new file in the root directory of your app
+          remote:  !     named 'requirements.txt' containing the requirement
+          remote:  !     '--editable .' (without quotes).
+          remote:  !     
+          remote:  !     Alternatively, if you wish to switch to another package
+          remote:  !     manager, we recommend uv, since it supports lockfiles, is
+          remote:  !     faster, and is actively maintained by a full-time team:
+          remote:  !     https://docs.astral.sh/uv/
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
         OUTPUT
       end
     end
   end
+
+  context 'when there are multiple package manager files' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/multiple_package_managers', allow_failure: true) }
+
+    it 'fails the build with an informative error message' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Python app detected
+          remote: 
+          remote:  !     Error: Multiple Python package manager files were found.
+          remote:  !     
+          remote:  !     Exactly one package manager file should be present in your app's
+          remote:  !     source code, however, several were found:
+          remote:  !     
+          remote:  !     Pipfile.lock (Pipenv)
+          remote:  !     requirements.txt (pip)
+          remote:  !     poetry.lock (Poetry)
+          remote:  !     uv.lock (uv)
+          remote:  !     
+          remote:  !     Previously, the buildpack guessed which package manager to use
+          remote:  !     and installed your dependencies with the first package manager
+          remote:  !     listed above. However, this implicit behaviour was deprecated
+          remote:  !     in November 2024 and is now no longer supported.
+          remote:  !     
+          remote:  !     You must decide which package manager you want to use with your
+          remote:  !     app, and then delete the file(s) and any config from the others.
+          remote:  !     
+          remote:  !     If you aren't sure which package manager to use, we recommend
+          remote:  !     trying uv, since it supports lockfiles, is extremely fast, and
+          remote:  !     is actively maintained by a full-time team:
+          remote:  !     https://docs.astral.sh/uv/
+          remote:  !     
+          remote:  !     Note: If you use a third-party uv or Poetry buildpack, you must
+          remote:  !     remove it from your app, since it's no longer required and the
+          remote:  !     requirements.txt file it generates will trigger this error. See:
+          remote:  !     https://devcenter.heroku.com/articles/managing-buildpacks#remove-classic-buildpacks
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        OUTPUT
+      end
+    end
+  end
+
+  context 'when the package manager has changed since the last build' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pip_basic') }
+
+    it 'clears the cache before installing with the new package manager' do
+      app.deploy do |app|
+        FileUtils.rm('bin/post_compile')
+        FileUtils.rm('requirements.txt')
+        FileUtils.cp(FIXTURE_DIR.join('uv_basic/pyproject.toml'), '.')
+        FileUtils.cp(FIXTURE_DIR.join('uv_basic/uv.lock'), '.')
+        app.commit!
+        app.push!
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
+          remote: -----> Python app detected
+          remote: -----> Using Python #{DEFAULT_PYTHON_MAJOR_VERSION} specified in .python-version
+          remote: -----> Discarding cache since:
+          remote:        - The package manager has changed from pip to uv
+          remote: -----> Installing Python #{DEFAULT_PYTHON_FULL_VERSION}
+          remote: -----> Installing uv #{UV_VERSION}
+          remote: -----> Installing dependencies using 'uv sync --locked --no-default-groups'
+          remote:        Resolved .+ packages in .+s
+          remote:        Prepared 1 package in .+s
+          remote:        Installed 1 package in .+s
+          remote:        Bytecode compiled 1 file in .+s
+          remote:         \\+ typing-extensions==4.15.0
+          remote: -----> Saving cache
+          remote: -----> Discovering process types
+        REGEX
+      end
+    end
+  end
 end
diff --git a/spec/hatchet/pip_spec.rb b/spec/hatchet/pip_spec.rb
index 704a65c4b..07e53f55c 100644
--- a/spec/hatchet/pip_spec.rb
+++ b/spec/hatchet/pip_spec.rb
@@ -2,199 +2,454 @@
 
 require_relative '../spec_helper'
 
-RSpec.shared_examples 'installs successfully using pip' do
-  it 'installs successfully using pip' do
-    app.deploy do |app|
-      expect(app.output).to include('Installing requirements with pip')
-      expect(app.output).to include('Successfully installed')
-    end
-  end
-end
-
-RSpec.describe 'Pip support' do
+RSpec.describe 'pip support' do
   context 'when requirements.txt is unchanged since the last build' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/python_version_unspecified') }
+    let(:buildpacks) { [:default, 'heroku-community/inline'] }
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pip_basic', buildpacks:) }
 
-    it 're-uses packages from the cache' do
+    it 'installs successfully using pip and on rebuilds uses the cache' do
       app.deploy do |app|
         expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
           remote: -----> Python app detected
-          remote: -----> No Python version was specified. Using the buildpack default: python-#{DEFAULT_PYTHON_VERSION}
-          remote:        To use a different version, see: https://devcenter.heroku.com/articles/python-runtimes
-          remote: -----> Installing python-#{DEFAULT_PYTHON_VERSION}
-          remote: -----> Installing pip #{PIP_VERSION}, setuptools #{SETUPTOOLS_VERSION} and wheel #{WHEEL_VERSION}
-          remote: -----> Installing SQLite3
-          remote: -----> Installing requirements with pip
-          remote:        Collecting urllib3 \\(from -r requirements.txt \\(line 1\\)\\)
-          remote:          Downloading urllib3-.*
-          remote:        Downloading urllib3-.*
-          remote:        Installing collected packages: urllib3
-          remote:        Successfully installed urllib3-.*
+          remote: -----> Using Python #{DEFAULT_PYTHON_MAJOR_VERSION} specified in .python-version
+          remote: -----> Installing Python #{DEFAULT_PYTHON_FULL_VERSION}
+          remote: -----> Installing pip #{PIP_VERSION}
+          remote: -----> Installing dependencies using 'pip install -r requirements.txt'
+          remote:        Collecting typing-extensions==4.15.0 \\(from -r requirements.txt \\(line 5\\)\\)
+          remote:          Downloading typing_extensions-4.15.0-py3-none-any.whl.metadata \\(3.3 kB\\)
+          remote:        Downloading typing_extensions-4.15.0-py3-none-any.whl \\(44 kB\\)
+          remote:        Installing collected packages: typing-extensions
+          remote:        Successfully installed typing-extensions-4.15.0
+          remote: -----> Running bin/post_compile hook
+          remote:        BUILD_DIR=/tmp/build_.+
+          remote:        CACHE_DIR=/tmp/codon/tmp/cache
+          remote:        C_INCLUDE_PATH=/app/.heroku/python/include
+          remote:        CPLUS_INCLUDE_PATH=/app/.heroku/python/include
+          remote:        ENV_DIR=/tmp/.+
+          remote:        LANG=en_US.UTF-8
+          remote:        LD_LIBRARY_PATH=/app/.heroku/python/lib
+          remote:        LIBRARY_PATH=/app/.heroku/python/lib
+          remote:        PATH=/app/.heroku/python/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+          remote:        PIP_DISABLE_PIP_VERSION_CHECK=1
+          remote:        PKG_CONFIG_PATH=/app/.heroku/python/lib/pkg-config
+          remote:        PYTHONUNBUFFERED=1
+          remote: -----> Saving cache
+          remote: 
+          remote:  !     Note: We recently added support for the package manager uv:
+          remote:  !     https://devcenter.heroku.com/changelog-items/3238
+          remote:  !     
+          remote:  !     It's now our recommended Python package manager, since it
+          remote:  !     supports lockfiles, is faster, gives more helpful error
+          remote:  !     messages, and is actively maintained by a full-time team.
+          remote:  !     
+          remote:  !     If you haven't tried it yet, we suggest you take a look!
+          remote:  !     https://docs.astral.sh/uv/
+          remote: 
+          remote: -----> Inline app detected
+          remote: LANG=en_US.UTF-8
+          remote: LD_LIBRARY_PATH=/app/.heroku/python/lib
+          remote: LIBRARY_PATH=/app/.heroku/python/lib
+          remote: PATH=/app/.heroku/python/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+          remote: PIP_DISABLE_PIP_VERSION_CHECK=1
+          remote: PYTHONHOME=/app/.heroku/python
+          remote: PYTHONPATH=/app
+          remote: PYTHONUNBUFFERED=true
+          remote: 
+          remote: \\['',
+          remote:  '/app',
+          remote:  '/app/.heroku/python/lib/python314.zip',
+          remote:  '/app/.heroku/python/lib/python3.14',
+          remote:  '/app/.heroku/python/lib/python3.14/lib-dynload',
+          remote:  '/app/.heroku/python/lib/python3.14/site-packages'\\]
+          remote: 
+          remote: pip #{PIP_VERSION} from /app/.heroku/python/lib/python3.14/site-packages/pip \\(python 3.14\\)
+          remote: Package           Version
+          remote: ----------------- -------
+          remote: pip               #{PIP_VERSION}
+          remote: typing_extensions 4.15.0
+          remote: 
+          remote: <module 'typing_extensions' from '/app/.heroku/python/lib/python3.14/site-packages/typing_extensions.py'>
+          remote: 
+          remote: \\{
+          remote:   "cache_restore_duration": [0-9.]+,
+          remote:   "cache_save_duration": [0-9.]+,
+          remote:   "cache_status": "empty",
+          remote:   "dependencies_install_duration": [0-9.]+,
+          remote:   "django_collectstatic_duration": [0-9.]+,
+          remote:   "nltk_downloader_duration": [0-9.]+,
+          remote:   "package_manager": "pip",
+          remote:   "package_manager_install_duration": [0-9.]+,
+          remote:   "pip_version": "#{PIP_VERSION}",
+          remote:   "post_compile_hook": true,
+          remote:   "post_compile_hook_duration": [0-9.]+,
+          remote:   "pre_compile_hook": false,
+          remote:   "python_install_duration": [0-9.]+,
+          remote:   "python_version": "#{DEFAULT_PYTHON_FULL_VERSION}",
+          remote:   "python_version_major": "3.14",
+          remote:   "python_version_origin": ".python-version",
+          remote:   "python_version_outdated": false,
+          remote:   "python_version_pinned": false,
+          remote:   "python_version_requested": "3.14",
+          remote:   "total_duration": [0-9.]+
+          remote: \\}
         REGEX
+
         app.commit!
         app.push!
-        expect(clean_output(app.output)).to include(<<~OUTPUT)
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
           remote: -----> Python app detected
-          remote: -----> No Python version was specified. Using the same version as the last build: python-#{DEFAULT_PYTHON_VERSION}
-          remote:        To use a different version, see: https://devcenter.heroku.com/articles/python-runtimes
-          remote: -----> No change in requirements detected, installing from cache
-          remote: -----> Using cached install of python-#{DEFAULT_PYTHON_VERSION}
-          remote: -----> Installing pip #{PIP_VERSION}, setuptools #{SETUPTOOLS_VERSION} and wheel #{WHEEL_VERSION}
-          remote: -----> Installing SQLite3
-          remote: -----> Installing requirements with pip
-          remote: -----> Discovering process types
+          remote: -----> Using Python #{DEFAULT_PYTHON_MAJOR_VERSION} specified in .python-version
+          remote: -----> Restoring cache
+          remote: -----> Using cached install of Python #{DEFAULT_PYTHON_FULL_VERSION}
+          remote: -----> Installing pip #{PIP_VERSION}
+          remote: -----> Installing dependencies using 'pip install -r requirements.txt'
+          remote:        Requirement already satisfied: typing-extensions==4.15.0 \\(from -r requirements.txt \\(line 5\\)\\) \\(4.15.0\\)
+          remote: -----> Running bin/post_compile hook
+          remote:        .+
+          remote: -----> Saving cache
+        REGEX
+
+        # For historical reasons pip is made available at run-time too, unlike some of the other package managers.
+        expect(normalize_trailing_newlines(app.run('bin/print-env-vars.sh && pip --version'))).to eq(<<~OUTPUT)
+          DYNO_RAM=512
+          FORWARDED_ALLOW_IPS=*
+          GUNICORN_CMD_ARGS=--access-logfile -
+          LANG=en_US.UTF-8
+          LD_LIBRARY_PATH=/app/.heroku/python/lib
+          LIBRARY_PATH=/app/.heroku/python/lib
+          PATH=/app/.heroku/python/bin:/usr/local/bin:/usr/bin:/bin
+          PIP_DISABLE_PIP_VERSION_CHECK=1
+          PYTHONHOME=/app/.heroku/python
+          PYTHONPATH=/app
+          PYTHONUNBUFFERED=true
+          WEB_CONCURRENCY=2
+          WEB_CONCURRENCY_SET_BY=heroku/python
+          pip #{PIP_VERSION} from /app/.heroku/python/lib/python3.14/site-packages/pip (python 3.14)
         OUTPUT
+        expect($CHILD_STATUS.exitstatus).to eq(0)
       end
     end
   end
 
   context 'when requirements.txt has changed since the last build' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/python_version_unspecified') }
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pip_basic') }
 
     it 'clears the cache before installing the packages again' do
       app.deploy do |app|
-        File.write('requirements.txt', 'six', mode: 'a')
+        # The test fixture's requirements.txt is a symlink to a requirements file in a subdirectory in
+        # order to test that symlinked requirements files work in general and with cache invalidation.
+        File.write('requirements/prod.txt', 'six==1.17.0', mode: 'a')
+        FileUtils.rm('bin/post_compile')
         app.commit!
         app.push!
-        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
           remote: -----> Python app detected
-          remote: -----> No Python version was specified. Using the same version as the last build: python-#{DEFAULT_PYTHON_VERSION}
-          remote:        To use a different version, see: https://devcenter.heroku.com/articles/python-runtimes
-          remote: -----> Requirements file has been changed, clearing cached dependencies
-          remote: -----> Installing python-#{DEFAULT_PYTHON_VERSION}
-          remote: -----> Installing pip #{PIP_VERSION}, setuptools #{SETUPTOOLS_VERSION} and wheel #{WHEEL_VERSION}
-          remote: -----> Installing SQLite3
-          remote: -----> Installing requirements with pip
-          remote:        Collecting urllib3 \\(from -r requirements.txt \\(line 1\\)\\)
-          remote:          Downloading urllib3-.*
-          remote:        Collecting six \\(from -r requirements.txt \\(line 2\\)\\)
-          remote:          Downloading six-.*
-          remote:        Downloading urllib3-.*
-          remote:        Downloading six-.*
-          remote:        Installing collected packages: urllib3, six
-          remote:        Successfully installed six-.* urllib3-.*
-        REGEX
+          remote: -----> Using Python #{DEFAULT_PYTHON_MAJOR_VERSION} specified in .python-version
+          remote: -----> Discarding cache since:
+          remote:        - The contents of requirements.txt changed
+          remote: -----> Installing Python #{DEFAULT_PYTHON_FULL_VERSION}
+          remote: -----> Installing pip #{PIP_VERSION}
+          remote: -----> Installing dependencies using 'pip install -r requirements.txt'
+          remote:        Collecting typing-extensions==4.15.0 (from -r requirements.txt (line 5))
+          remote:          Downloading typing_extensions-4.15.0-py3-none-any.whl.metadata (3.3 kB)
+          remote:        Collecting six==1.17.0 (from -r requirements.txt (line 6))
+          remote:          Downloading six-1.17.0-py2.py3-none-any.whl.metadata (1.7 kB)
+          remote:        Downloading typing_extensions-4.15.0-py3-none-any.whl (44 kB)
+          remote:        Downloading six-1.17.0-py2.py3-none-any.whl (11 kB)
+          remote:        Installing collected packages: typing-extensions, six
+          remote:        Successfully installed six-1.17.0 typing-extensions-4.15.0
+          remote: -----> Saving cache
+        OUTPUT
       end
     end
   end
 
-  context 'when requirements.txt contains popular compiled packages' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/requirements_compiled') }
-
-    include_examples 'installs successfully using pip'
-  end
-
-  context 'when requirements.txt contains Git requirements URLs' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/requirements_git') }
-
-    include_examples 'installs successfully using pip'
-  end
-
-  context 'when requirements.txt contains editable requirements' do
+  context 'when requirements.txt contains editable requirements (both VCS and local package)' do
     let(:buildpacks) { [:default, 'heroku-community/inline'] }
-    let(:app) { Hatchet::Runner.new('spec/fixtures/requirements_editable', buildpacks:) }
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pip_editable', buildpacks:) }
 
-    it 'rewrites .pth, .egg-link and finder paths correctly for hooks, later buildpacks, runtime and cached builds' do
+    it 'rewrites .pth and finder paths correctly for hooks, later buildpacks, runtime and cached builds' do
       app.deploy do |app|
         expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
-          remote: -----> Running post-compile hook
-          remote: easy-install.pth:/app/.heroku/src/gunicorn
-          remote: easy-install.pth:/tmp/build_.*/packages/local_package_setup_py
-          remote: __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.*/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
-          remote: gunicorn.egg-link:/app/.heroku/src/gunicorn
-          remote: local-package-setup-py.egg-link:/tmp/build_.*/packages/local_package_setup_py
-          remote: 
-          remote: Running entrypoint for the pyproject.toml-based local package: Hello pyproject.toml!
-          remote: Running entrypoint for the setup.py-based local package: Hello setup.py!
-          remote: Running entrypoint for the VCS package: gunicorn \\(version 20.1.0\\)
+          remote: -----> Running bin/post_compile hook
+          remote:        __editable___gunicorn_23_0_0_finder.py:/app/.heroku/python/src/gunicorn/gunicorn'}
+          remote:        __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.+/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
+          remote:        __editable___local_package_setup_py_0_0_1_finder.py:/tmp/build_.+/packages/local_package_setup_py/local_package_setup_py'}
+          remote:        
+          remote:        Running entrypoint for the pyproject.toml-based local package: Hello from pyproject.toml!
+          remote:        Running entrypoint for the setup.py-based local package: Hello from setup.py!
+          remote:        Running entrypoint for the VCS package: gunicorn \\(version 23.0.0\\)
+          remote: -----> Saving cache
+          .+
           remote: -----> Inline app detected
-          remote: easy-install.pth:/app/.heroku/src/gunicorn
-          remote: easy-install.pth:/tmp/build_.*/packages/local_package_setup_py
-          remote: __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.*/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
-          remote: gunicorn.egg-link:/app/.heroku/src/gunicorn
-          remote: local-package-setup-py.egg-link:/tmp/build_.*/packages/local_package_setup_py
-          remote: 
-          remote: Running entrypoint for the pyproject.toml-based local package: Hello pyproject.toml!
-          remote: Running entrypoint for the setup.py-based local package: Hello setup.py!
-          remote: Running entrypoint for the VCS package: gunicorn \\(version 20.1.0\\)
+          remote: __editable___gunicorn_23_0_0_finder.py:/app/.heroku/python/src/gunicorn/gunicorn'}
+          remote: __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.+/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
+          remote: __editable___local_package_setup_py_0_0_1_finder.py:/tmp/build_.+/packages/local_package_setup_py/local_package_setup_py'}
+          remote: 
+          remote: Running entrypoint for the pyproject.toml-based local package: Hello from pyproject.toml!
+          remote: Running entrypoint for the setup.py-based local package: Hello from setup.py!
+          remote: Running entrypoint for the VCS package: gunicorn \\(version 23.0.0\\)
         REGEX
 
         # Test rewritten paths work at runtime.
-        expect(app.run('bin/test-entrypoints')).to include(<<~OUTPUT)
-          easy-install.pth:/app/.heroku/src/gunicorn
-          easy-install.pth:/app/packages/local_package_setup_py
+        expect(app.run('bin/test-entrypoints.sh')).to include(<<~OUTPUT)
+          __editable___gunicorn_23_0_0_finder.py:/app/.heroku/python/src/gunicorn/gunicorn'}
           __editable___local_package_pyproject_toml_0_0_1_finder.py:/app/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
-          gunicorn.egg-link:/app/.heroku/src/gunicorn
-          local-package-setup-py.egg-link:/app/packages/local_package_setup_py
+          __editable___local_package_setup_py_0_0_1_finder.py:/app/packages/local_package_setup_py/local_package_setup_py'}
 
-          Running entrypoint for the pyproject.toml-based local package: Hello pyproject.toml!
-          Running entrypoint for the setup.py-based local package: Hello setup.py!
-          Running entrypoint for the VCS package: gunicorn (version 20.1.0)
+          Running entrypoint for the pyproject.toml-based local package: Hello from pyproject.toml!
+          Running entrypoint for the setup.py-based local package: Hello from setup.py!
+          Running entrypoint for the VCS package: gunicorn (version 23.0.0)
         OUTPUT
 
         # Test that the cached .pth files work correctly.
         app.commit!
         app.push!
         expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
-          remote: -----> Running post-compile hook
-          remote: easy-install.pth:/app/.heroku/src/gunicorn
-          remote: easy-install.pth:/tmp/build_.*/packages/local_package_setup_py
-          remote: __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.*/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
-          remote: gunicorn.egg-link:/app/.heroku/src/gunicorn
-          remote: local-package-setup-py.egg-link:/tmp/build_.*/packages/local_package_setup_py
-          remote: 
-          remote: Running entrypoint for the pyproject.toml-based local package: Hello pyproject.toml!
-          remote: Running entrypoint for the setup.py-based local package: Hello setup.py!
-          remote: Running entrypoint for the VCS package: gunicorn \\(version 20.1.0\\)
+          remote: -----> Running bin/post_compile hook
+          remote:        __editable___gunicorn_23_0_0_finder.py:/app/.heroku/python/src/gunicorn/gunicorn'}
+          remote:        __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.+/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
+          remote:        __editable___local_package_setup_py_0_0_1_finder.py:/tmp/build_.+/packages/local_package_setup_py/local_package_setup_py'}
+          remote:        
+          remote:        Running entrypoint for the pyproject.toml-based local package: Hello from pyproject.toml!
+          remote:        Running entrypoint for the setup.py-based local package: Hello from setup.py!
+          remote:        Running entrypoint for the VCS package: gunicorn \\(version 23.0.0\\)
+          remote: -----> Saving cache
+          .+
           remote: -----> Inline app detected
-          remote: easy-install.pth:/app/.heroku/src/gunicorn
-          remote: easy-install.pth:/tmp/build_.*/packages/local_package_setup_py
-          remote: __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.*/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
-          remote: gunicorn.egg-link:/app/.heroku/src/gunicorn
-          remote: local-package-setup-py.egg-link:/tmp/build_.*/packages/local_package_setup_py
-          remote: 
-          remote: Running entrypoint for the pyproject.toml-based local package: Hello pyproject.toml!
-          remote: Running entrypoint for the setup.py-based local package: Hello setup.py!
-          remote: Running entrypoint for the VCS package: gunicorn \\(version 20.1.0\\)
+          remote: __editable___gunicorn_23_0_0_finder.py:/app/.heroku/python/src/gunicorn/gunicorn'}
+          remote: __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.+/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
+          remote: __editable___local_package_setup_py_0_0_1_finder.py:/tmp/build_.+/packages/local_package_setup_py/local_package_setup_py'}
+          remote: 
+          remote: Running entrypoint for the pyproject.toml-based local package: Hello from pyproject.toml!
+          remote: Running entrypoint for the setup.py-based local package: Hello from setup.py!
+          remote: Running entrypoint for the VCS package: gunicorn \\(version 23.0.0\\)
         REGEX
+        # Test that the VCS repo checkout was cached correctly.
+        expect(app.output).to include(<<~OUTPUT)
+          remote:        Obtaining gunicorn from git+https://github.com/benoitc/gunicorn@56b5ad87f8d72a674145c273ed8f547513c2b409#egg=gunicorn (from -r requirements.txt (line 5))        
+          remote:          Skipping because already up-to-date.        
+        OUTPUT
       end
     end
   end
 
-  context 'when there is only a setup.py' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/setup_py_only') }
+  # This checks that the pip bootstrap works even with older bundled pip, and that our
+  # chosen Pip version also supports our oldest supported Python version.
+  context 'when using our oldest supported Python version' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pip_oldest_python') }
 
-    it 'installs packages from setup.py' do
+    it 'installs successfully' do
       app.deploy do |app|
-        expect(app.output).to include('Running setup.py develop for test')
-        expect(app.output).to include('Successfully installed six')
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Python app detected
+          remote: -----> Using Python 3.10.0 specified in runtime.txt
+          remote: 
+          remote:  !     Warning: The runtime.txt file is deprecated.
+          remote:  !     
+          remote:  !     The runtime.txt file is deprecated since it has been replaced
+          remote:  !     by the more widely supported .python-version file:
+          remote:  !     https://devcenter.heroku.com/changelog-items/3141
+          remote:  !     
+          remote:  !     Please switch to using a .python-version file instead.
+          remote:  !     
+          remote:  !     Delete your runtime.txt file and create a new file in the
+          remote:  !     root directory of your app named:
+          remote:  !     .python-version
+          remote:  !     
+          remote:  !     Make sure to include the '.' character at the start of the
+          remote:  !     filename. Don't add a file extension such as '.txt'.
+          remote:  !     
+          remote:  !     In the new file, specify your app's major Python version number
+          remote:  !     only. Don't include quotes or a 'python-' prefix.
+          remote:  !     
+          remote:  !     For example, to request the latest version of Python 3.10,
+          remote:  !     update your .python-version file so it contains exactly:
+          remote:  !     3.10
+          remote:  !     
+          remote:  !     We strongly recommend that you don't specify the Python patch
+          remote:  !     version number, since it will pin your app to an exact Python
+          remote:  !     version and so stop your app from receiving security updates
+          remote:  !     each time it builds.
+          remote:  !     
+          remote:  !     In the future support for runtime.txt will be removed and
+          remote:  !     this warning will be made an error.
+          remote: 
+          remote: 
+          remote:  !     Warning: Support for Python 3.10 is deprecated!
+          remote:  !     
+          remote:  !     Python 3.10 will reach its upstream end-of-life in October 2026,
+          remote:  !     at which point it will no longer receive security updates:
+          remote:  !     https://devguide.python.org/versions/#supported-versions
+          remote:  !     
+          remote:  !     As such, support for Python 3.10 will be removed from this
+          remote:  !     buildpack on 6th January 2027.
+          remote:  !     
+          remote:  !     Upgrade to a newer Python version as soon as possible, by
+          remote:  !     changing the version in your runtime.txt file.
+          remote:  !     
+          remote:  !     For more information, see:
+          remote:  !     https://devcenter.heroku.com/articles/python-support#supported-python-versions
+          remote: 
+          remote: 
+          remote:  !     Warning: A Python patch update is available!
+          remote:  !     
+          remote:  !     Your app is using Python 3.10.0, however, there is a newer
+          remote:  !     patch release of Python 3.10 available: #{LATEST_PYTHON_3_10}
+          remote:  !     
+          remote:  !     It is important to always use the latest patch version of
+          remote:  !     Python to keep your app secure.
+          remote:  !     
+          remote:  !     Update your runtime.txt file to use the new version.
+          remote:  !     
+          remote:  !     We strongly recommend that you don't pin your app to an
+          remote:  !     exact Python version such as 3.10.0, and instead only specify
+          remote:  !     the major Python version of 3.10 in your runtime.txt file.
+          remote:  !     This will allow your app to receive the latest available Python
+          remote:  !     patch version automatically and prevent this warning.
+          remote: 
+          remote: -----> Installing Python 3.10.0
+          remote: -----> Installing pip #{PIP_VERSION} and setuptools #{SETUPTOOLS_VERSION}
+          remote: -----> Installing dependencies using 'pip install -r requirements.txt'
+          remote:        Collecting typing-extensions==4.15.0 (from -r requirements.txt (line 2))
+          remote:          Downloading typing_extensions-4.15.0-py3-none-any.whl.metadata (3.3 kB)
+          remote:        Downloading typing_extensions-4.15.0-py3-none-any.whl (44 kB)
+          remote:        Installing collected packages: typing-extensions
+          remote:        Successfully installed typing-extensions-4.15.0
+          remote: -----> Saving cache
+        OUTPUT
+        app.commit!
+        app.push!
+        # Test that our regex for cleaning up the "Requirement already satisfied" lines also works
+        # with the relative paths output when pip is run with Python 3.10 and older. This and the
+        # regex variant can be removed once support for Python 3.10 and older is dropped.
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Installing dependencies using 'pip install -r requirements.txt'
+          remote:        Requirement already satisfied: typing-extensions==4.15.0 (from -r requirements.txt (line 2)) (4.15.0)
+          remote: -----> Saving cache
+        OUTPUT
+      end
+    end
+  end
+
+  context 'when requirements.txt contains a package that needs compiling against the Python headers' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pip_compiled') }
+
+    it 'installs successfully using pip' do
+      app.deploy do |app|
+        expect(app.output).to include('Building wheel for extension.dist')
       end
     end
   end
 
-  context 'when there is both a requirements.txt and setup.py' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/requirements_txt_and_setup_py') }
+  context 'when requirements.txt contains an invalid requirement' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pip_invalid_requirement', allow_failure: true) }
 
-    it 'installs packages only from requirements.txt' do
+    it 'aborts the build and displays the pip error' do
       app.deploy do |app|
         expect(clean_output(app.output)).to include(<<~OUTPUT)
-          remote: -----> Installing requirements with pip
-          remote:        Collecting urllib3 (from -r requirements.txt (line 1))
+          remote: -----> Installing dependencies using 'pip install -r requirements.txt'
+          remote:        ERROR: Invalid requirement: 'an-invalid-requirement!': Expected semicolon (after name with no version specifier) or end
+          remote:            an-invalid-requirement!
+          remote:                                  ^ (from line 1 of requirements.txt)
+          remote: 
+          remote:  !     Error: Unable to install dependencies using pip.
+          remote:  !     
+          remote:  !     See the log output above for more information.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
         OUTPUT
-        expect(app.output).not_to include('Running setup.py develop')
       end
     end
   end
 
   context 'when requirements.txt contains GDAL but the GDAL C++ library is missing' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/requirements_gdal', allow_failure: true) }
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pip_gdal', allow_failure: true) }
 
     it 'outputs instructions for how to resolve the build failure' do
       app.deploy do |app|
         expect(clean_output(app.output)).to include(<<~OUTPUT)
-          remote:  !     Hello! Package installation failed since the GDAL library was not found.
+          remote:        ERROR: Failed to build 'GDAL' when getting requirements to build wheel
+          remote: 
+          remote:  !     Error: Package installation failed since the GDAL library wasn't found.
+          remote:  !     
           remote:  !     For GDAL, GEOS and PROJ support, use the Geo buildpack alongside the Python buildpack:
           remote:  !     https://github.com/heroku/heroku-geo-buildpack
+          remote: 
+          remote: 
+          remote:  !     Error: Unable to install dependencies using pip.
+          remote:  !     
+          remote:  !     See the log output above for more information.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        OUTPUT
+      end
+    end
+  end
+
+  context 'when requirements.txt contains an old version of Celery with invalid metadata' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pip_legacy_celery', allow_failure: true) }
+
+    it 'outputs instructions for how to resolve the build failure' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote:        ERROR: No matching distribution found for celery==5.2.0
+          remote: 
+          remote:  !     Error: One of your dependencies contains broken metadata.
+          remote:  !     
+          remote:  !     Newer versions of pip reject packages that use invalid versions
+          remote:  !     in their metadata (such as Celery older than v5.2.1).
+          remote:  !     
+          remote:  !     Try upgrading to a newer version of the affected package.
+          remote:  !     
+          remote:  !     For more help, see:
+          remote:  !     https://devcenter.heroku.com/changelog-items/3073
+          remote: 
+          remote: 
+          remote:  !     Error: Unable to install dependencies using pip.
+          remote:  !     
+          remote:  !     See the log output above for more information.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        OUTPUT
+      end
+    end
+  end
+
+  context 'when requirements.txt contains pysqlite3' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pip_pysqlite3', allow_failure: true) }
+
+    it 'outputs instructions for how to resolve the build failure' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote:        × Failed to build installable wheels for some pyproject.toml based projects
+          remote:        ╰─> pysqlite3
+          remote: 
+          remote:  !     Error: Package installation failed since SQLite headers weren't found.
+          remote:  !     
+          remote:  !     The Python buildpack no longer installs the SQLite headers
+          remote:  !     package since most apps don't require it.
+          remote:  !     
+          remote:  !     If you're trying to install the `pysqlite3` package, we
+          remote:  !     recommend using the virtually identical `sqlite3` module in
+          remote:  !     Python's standard library instead:
+          remote:  !     https://docs.python.org/3/library/sqlite3.html
+          remote:  !     
+          remote:  !     To do this:
+          remote:  !     1. Remove the `pysqlite3` package from your dependencies.
+          remote:  !     2. Replace any `pysqlite3` imports in your app with `sqlite3`.
+          remote:  !     
+          remote:  !     Alternatively, if you can't use the `sqlite3` stdlib module,
+          remote:  !     update your `pysqlite3` package to 0.6.0 or newer, since the
+          remote:  !     newer versions are published with pre-compiled wheels and so
+          remote:  !     don't need the SQLite headers to be installed.
+          remote: 
+          remote: 
+          remote:  !     Error: Unable to install dependencies using pip.
+          remote:  !     
+          remote:  !     See the log output above for more information.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
         OUTPUT
       end
     end
diff --git a/spec/hatchet/pipenv_spec.rb b/spec/hatchet/pipenv_spec.rb
index ff5b5ba1c..c7080e98e 100644
--- a/spec/hatchet/pipenv_spec.rb
+++ b/spec/hatchet/pipenv_spec.rb
@@ -2,245 +2,385 @@
 
 require_relative '../spec_helper'
 
-RSpec.shared_examples 'builds using Pipenv with the requested Python version' do |python_version|
-  it "builds with Python #{python_version}" do
-    app.deploy do |app|
-      expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
-        remote: -----> Python app detected
-        remote: -----> Using Python version specified in Pipfile.lock
-        remote: -----> Installing python-#{python_version}
-        remote: -----> Installing pip #{PIP_VERSION}, setuptools #{SETUPTOOLS_VERSION} and wheel #{WHEEL_VERSION}
-        remote: -----> Installing dependencies with Pipenv #{PIPENV_VERSION}
-        remote:        Installing dependencies from Pipfile.lock \\(.+\\)...
-        remote: -----> Installing SQLite3
-      REGEX
-    end
-  end
-end
-
-RSpec.shared_examples 'aborts the build with a runtime not available message (Pipenv)' do |requested_version|
-  it 'aborts the build with a runtime not available message' do
-    app.deploy do |app|
-      expect(clean_output(app.output)).to include(<<~OUTPUT)
-        remote: -----> Python app detected
-        remote: -----> Using Python version specified in Pipfile.lock
-        remote:  !     
-        remote:  !     Requested runtime 'python-#{requested_version}' is not available for this stack (#{app.stack}).
-        remote:  !     
-        remote:  !     For a list of the supported Python versions, see:
-        remote:  !     https://devcenter.heroku.com/articles/python-support#supported-runtimes
-        remote:  !     
-      OUTPUT
-    end
-  end
-end
-
 RSpec.describe 'Pipenv support' do
-  context 'without a Pipfile.lock' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_no_lockfile') }
+  context 'with a Pipfile.lock that is unchanged since the last build' do
+    let(:buildpacks) { [:default, 'heroku-community/inline'] }
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_basic', buildpacks:) }
 
-    it 'builds with the default Python version using just the Pipfile' do
+    it 'installs successfully using Pipenv and on rebuilds uses the cache' do
       app.deploy do |app|
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
+          remote: -----> Python app detected
+          remote: -----> Using Python #{DEFAULT_PYTHON_MAJOR_VERSION} specified in Pipfile.lock
+          remote: -----> Installing Python #{DEFAULT_PYTHON_FULL_VERSION}
+          remote: -----> Installing Pipenv #{PIPENV_VERSION}
+          remote: -----> Installing dependencies using 'pipenv install --deploy'
+          remote: -----> Running bin/post_compile hook
+          remote:        BUILD_DIR=/tmp/build_.+
+          remote:        CACHE_DIR=/tmp/codon/tmp/cache
+          remote:        C_INCLUDE_PATH=/app/.heroku/python/include
+          remote:        CPLUS_INCLUDE_PATH=/app/.heroku/python/include
+          remote:        ENV_DIR=/tmp/.+
+          remote:        LANG=en_US.UTF-8
+          remote:        LD_LIBRARY_PATH=/app/.heroku/python/lib
+          remote:        LIBRARY_PATH=/app/.heroku/python/lib
+          remote:        PATH=/app/.heroku/python/pipenv/bin:/app/.heroku/python/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+          remote:        PIPENV_SYSTEM=1
+          remote:        PIPENV_VERBOSITY=-1
+          remote:        PKG_CONFIG_PATH=/app/.heroku/python/lib/pkg-config
+          remote:        PYTHONUNBUFFERED=1
+          remote:        VIRTUAL_ENV=/app/.heroku/python
+          remote: -----> Saving cache
+          remote: 
+          remote:  !     Note: We recently added support for the package manager uv:
+          remote:  !     https://devcenter.heroku.com/changelog-items/3238
+          remote:  !     
+          remote:  !     It's now our recommended Python package manager, since it
+          remote:  !     supports lockfiles, is faster, gives more helpful error
+          remote:  !     messages, and is actively maintained by a full-time team.
+          remote:  !     
+          remote:  !     If you haven't tried it yet, we suggest you take a look!
+          remote:  !     https://docs.astral.sh/uv/
+          remote: 
+          remote: -----> Inline app detected
+          remote: LANG=en_US.UTF-8
+          remote: LD_LIBRARY_PATH=/app/.heroku/python/lib
+          remote: LIBRARY_PATH=/app/.heroku/python/lib
+          remote: PATH=/app/.heroku/python/bin:/app/.heroku/python/pipenv/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+          remote: PIPENV_SYSTEM=1
+          remote: PIPENV_VERBOSITY=-1
+          remote: PYTHONHOME=/app/.heroku/python
+          remote: PYTHONPATH=/app
+          remote: PYTHONUNBUFFERED=true
+          remote: VIRTUAL_ENV=/app/.heroku/python
+          remote: 
+          remote: \\['',
+          remote:  '/app',
+          remote:  '/app/.heroku/python/lib/python314.zip',
+          remote:  '/app/.heroku/python/lib/python3.14',
+          remote:  '/app/.heroku/python/lib/python3.14/lib-dynload',
+          remote:  '/app/.heroku/python/lib/python3.14/site-packages'\\]
+          remote: 
+          remote: pipenv, version #{PIPENV_VERSION}
+          remote: Package           Version
+          remote: ----------------- -+
+          remote: certifi           2026.1.4
+          remote: packaging         25.0
+          remote: typing_extensions 4.15.0
+          remote: 
+          remote: <module 'typing_extensions' from '/app/.heroku/python/lib/python3.14/site-packages/typing_extensions.py'>
+          remote: <module 'certifi' from '/app/.heroku/python/lib/python3.14/site-packages/certifi/__init__.py'>
+          remote: <module 'packaging' from '/app/.heroku/python/lib/python3.14/site-packages/packaging/__init__.py'>
+          remote: 
+          remote: \\{
+          remote:   "cache_restore_duration": [0-9.]+,
+          remote:   "cache_save_duration": [0-9.]+,
+          remote:   "cache_status": "empty",
+          remote:   "dependencies_install_duration": [0-9.]+,
+          remote:   "django_collectstatic_duration": [0-9.]+,
+          remote:   "nltk_downloader_duration": [0-9.]+,
+          remote:   "package_manager": "pipenv",
+          remote:   "package_manager_install_duration": [0-9.]+,
+          remote:   "pipenv_version": "#{PIPENV_VERSION}",
+          remote:   "post_compile_hook": true,
+          remote:   "post_compile_hook_duration": [0-9.]+,
+          remote:   "pre_compile_hook": false,
+          remote:   "python_install_duration": [0-9.]+,
+          remote:   "python_version": "#{DEFAULT_PYTHON_FULL_VERSION}",
+          remote:   "python_version_major": "3.14",
+          remote:   "python_version_origin": "Pipfile.lock",
+          remote:   "python_version_outdated": false,
+          remote:   "python_version_pinned": false,
+          remote:   "python_version_requested": "3.14",
+          remote:   "total_duration": [0-9.]+
+          remote: \\}
+        REGEX
+
+        app.commit!
+        app.push!
         expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
           remote: -----> Python app detected
-          remote:  !     No 'Pipfile.lock' found! We recommend you commit this into your repository.
-          remote: -----> No Python version was specified. Using the buildpack default: python-#{DEFAULT_PYTHON_VERSION}
-          remote:        To use a different version, see: https://devcenter.heroku.com/articles/python-runtimes
-          remote: -----> Installing python-#{DEFAULT_PYTHON_VERSION}
-          remote: -----> Installing pip #{PIP_VERSION}, setuptools #{SETUPTOOLS_VERSION} and wheel #{WHEEL_VERSION}
-          remote: -----> Installing dependencies with Pipenv #{PIPENV_VERSION}
-          remote:        The flag --skip-lock has been reintroduced \\(but is not recommended\\).  Without 
-          remote:        the lock resolver it is difficult to manage multiple package indexes, and hash 
-          remote:        checking is not provided.  However it can help manage installs with current 
-          remote:        deficiencies in locking across platforms.
-          remote:        Pipfile.lock not found, creating...
-          .+
-          remote:        Installing dependencies from Pipfile...
-          remote: -----> Installing SQLite3
+          remote: -----> Using Python #{DEFAULT_PYTHON_MAJOR_VERSION} specified in Pipfile.lock
+          remote: -----> Restoring cache
+          remote: -----> Using cached install of Python #{DEFAULT_PYTHON_FULL_VERSION}
+          remote: -----> Using cached Pipenv #{PIPENV_VERSION}
+          remote: -----> Installing dependencies using 'pipenv install --deploy'
+          remote: -----> Running bin/post_compile hook
+          remote:        .+
+          remote: -----> Saving cache
         REGEX
+
+        # For historical reasons Pipenv is made available at run-time too, unlike some of the other package managers.
+        expect(normalize_trailing_newlines(app.run('bin/print-env-vars.sh && pipenv --version'))).to eq(<<~OUTPUT)
+          DYNO_RAM=512
+          FORWARDED_ALLOW_IPS=*
+          GUNICORN_CMD_ARGS=--access-logfile -
+          LANG=en_US.UTF-8
+          LD_LIBRARY_PATH=/app/.heroku/python/lib
+          LIBRARY_PATH=/app/.heroku/python/lib
+          PATH=/app/.heroku/python/bin:/app/.heroku/python/pipenv/bin:/usr/local/bin:/usr/bin:/bin
+          PIPENV_SYSTEM=1
+          PIPENV_VERBOSITY=-1
+          PYTHONHOME=/app/.heroku/python
+          PYTHONPATH=/app
+          PYTHONUNBUFFERED=true
+          VIRTUAL_ENV=/app/.heroku/python
+          WEB_CONCURRENCY=2
+          WEB_CONCURRENCY_SET_BY=heroku/python
+          pipenv, version #{PIPENV_VERSION}
+        OUTPUT
+        expect($CHILD_STATUS.exitstatus).to eq(0)
       end
     end
   end
 
-  context 'with a Pipfile.lock but no Python version specified' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_python_version_unspecified') }
+  context 'when Pipfile.lock has changed since the last build' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_basic') }
 
-    it 'builds with the default Python version' do
+    it 'clears the cache before installing the packages again' do
       app.deploy do |app|
+        File.write('Pipfile.lock', "\n", mode: 'a')
+        FileUtils.rm('bin/post_compile')
+        app.commit!
+        app.push!
         expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
           remote: -----> Python app detected
-          remote: -----> No Python version was specified. Using the buildpack default: python-#{DEFAULT_PYTHON_VERSION}
-          remote:        To use a different version, see: https://devcenter.heroku.com/articles/python-runtimes
-          remote: -----> Installing python-#{DEFAULT_PYTHON_VERSION}
-          remote: -----> Installing pip #{PIP_VERSION}, setuptools #{SETUPTOOLS_VERSION} and wheel #{WHEEL_VERSION}
-          remote: -----> Installing dependencies with Pipenv #{PIPENV_VERSION}
-          remote:        Installing dependencies from Pipfile.lock \\(.+\\)...
-          remote: -----> Installing SQLite3
+          remote: -----> Using Python #{DEFAULT_PYTHON_MAJOR_VERSION} specified in Pipfile.lock
+          remote: -----> Discarding cache since:
+          remote:        - The contents of Pipfile.lock changed
+          remote: -----> Installing Python #{DEFAULT_PYTHON_FULL_VERSION}
+          remote: -----> Installing Pipenv #{PIPENV_VERSION}
+          remote: -----> Installing dependencies using 'pipenv install --deploy'
+          remote: -----> Saving cache
         REGEX
       end
     end
   end
 
-  context 'with a Pipfile.lock containing python_version 3.6' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_python_3.6', allow_failure: true) }
+  # As well as testing the Pipfile.lock `python_full_version` field, this also tests:
+  # 1. That `python_full_version` takes precedence over the `python_version` field.
+  # 2. That Pipenv works on the oldest Python version supported by all stacks.
+  # 3. That the security update available message works for Pipenv too.
+  context 'with a Pipfile.lock containing python_full_version 3.10.0' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_python_full_version') }
 
-    it 'aborts the build with an EOL message' do
+    it 'builds with the outdated Python version specified and displays a deprecation warning' do
       app.deploy do |app|
-        expect(clean_output(app.output)).to match(Regexp.new(<<~OUTPUT))
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
           remote: -----> Python app detected
-          remote: -----> Using Python version specified in Pipfile.lock
+          remote: -----> Using Python 3.10.0 specified in Pipfile.lock
+          remote: 
+          remote:  !     Warning: Support for Python 3.10 is deprecated!
           remote:  !     
-          remote:  !     Python 3.6 reached upstream end-of-life on December 23rd, 2021, and is
-          remote:  !     therefore no longer receiving security updates:
+          remote:  !     Python 3.10 will reach its upstream end-of-life in October 2026,
+          remote:  !     at which point it will no longer receive security updates:
           remote:  !     https://devguide.python.org/versions/#supported-versions
           remote:  !     
-          remote:  !     As such, it is no longer supported by this buildpack.
+          remote:  !     As such, support for Python 3.10 will be removed from this
+          remote:  !     buildpack on 6th January 2027.
           remote:  !     
-          remote:  !     Please upgrade to a newer Python version.
+          remote:  !     Upgrade to a newer Python version as soon as possible, by
+          remote:  !     changing the version in your Pipfile.lock file.
           remote:  !     
-          remote:  !     For a list of the supported Python versions, see:
-          remote:  !     https://devcenter.heroku.com/articles/python-support#supported-runtimes
+          remote:  !     For more information, see:
+          remote:  !     https://devcenter.heroku.com/articles/python-support#supported-python-versions
+          remote: 
+          remote: 
+          remote:  !     Warning: A Python patch update is available!
           remote:  !     
-        OUTPUT
+          remote:  !     Your app is using Python 3.10.0, however, there is a newer
+          remote:  !     patch release of Python 3.10 available: #{LATEST_PYTHON_3_10}
+          remote:  !     
+          remote:  !     It is important to always use the latest patch version of
+          remote:  !     Python to keep your app secure.
+          remote:  !     
+          remote:  !     Update your Pipfile.lock file to use the new version.
+          remote:  !     
+          remote:  !     We strongly recommend that you don't pin your app to an
+          remote:  !     exact Python version such as 3.10.0, and instead only specify
+          remote:  !     the major Python version of 3.10 in your Pipfile.lock file.
+          remote:  !     This will allow your app to receive the latest available Python
+          remote:  !     patch version automatically and prevent this warning.
+          remote: 
+          remote: -----> Installing Python 3.10.0
+          remote: -----> Installing Pipenv #{PIPENV_VERSION}
+          remote: -----> Installing dependencies using 'pipenv install --deploy'
+          remote: -----> Saving cache
+        REGEX
       end
     end
   end
 
-  context 'with a Pipfile.lock containing python_version 3.7' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_python_3.7', allow_failure: true) }
+  # TODO: Delete this test once pipenv_mismatched_python_version is re-enabled,
+  # since they mostly duplicate each other.
+  context 'when there is both a Pipfile.lock python_version and a .python-version file' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_python_version_and_python_version_file') }
 
-    it 'aborts the build with an EOL message' do
+    it 'builds with the Python version from the .python-version file' do
       app.deploy do |app|
-        expect(clean_output(app.output)).to match(Regexp.new(<<~OUTPUT))
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
+          remote: -----> Python app detected
+          remote: -----> Using Python 3.13 specified in .python-version
+          remote: -----> Installing Python #{LATEST_PYTHON_3_13}
+          remote: -----> Installing Pipenv #{PIPENV_VERSION}
+          remote: -----> Installing dependencies using 'pipenv install --deploy'
+          remote: -----> Saving cache
+        REGEX
+      end
+    end
+  end
+
+  context 'with a Pipfile.lock but no Python version specified' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_python_version_unspecified') }
+
+    it 'builds with the default Python version' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
           remote: -----> Python app detected
-          remote: -----> Using Python version specified in Pipfile.lock
+          remote: -----> No Python version was specified. Using the buildpack default: Python #{DEFAULT_PYTHON_MAJOR_VERSION}
+          remote: 
+          remote:  !     Warning: No Python version was specified.
           remote:  !     
-          remote:  !     Python 3.7 reached upstream end-of-life on June 27th, 2023, and is
-          remote:  !     therefore no longer receiving security updates:
-          remote:  !     https://devguide.python.org/versions/#supported-versions
+          remote:  !     Your app doesn't specify a Python version and so the buildpack
+          remote:  !     picked a default version for you.
           remote:  !     
-          remote:  !     As such, it is no longer supported by this buildpack.
+          remote:  !     Relying on this default version isn't recommended, since it
+          remote:  !     can change over time and may not be consistent with your local
+          remote:  !     development environment, CI or other instances of your app.
           remote:  !     
-          remote:  !     Please upgrade to a newer Python version.
+          remote:  !     Please configure an explicit Python version for your app.
           remote:  !     
-          remote:  !     For a list of the supported Python versions, see:
-          remote:  !     https://devcenter.heroku.com/articles/python-support#supported-runtimes
+          remote:  !     Create a new file in the root directory of your app named:
+          remote:  !     .python-version
           remote:  !     
-        OUTPUT
-      end
-    end
-  end
-
-  context 'with a Pipfile.lock containing python_version 3.8' do
-    let(:allow_failure) { false }
-    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_python_3.8', allow_failure:) }
-
-    context 'when using Heroku-20', stacks: %w[heroku-20] do
-      it 'builds with the latest Python 3.8 but shows a deprecation warning' do
-        app.deploy do |app|
-          expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
-            remote: -----> Python app detected
-            remote: -----> Using Python version specified in Pipfile.lock
-            remote:  !     
-            remote:  !     Python 3.8 will reach its upstream end-of-life in October 2024, at which
-            remote:  !     point it will no longer receive security updates:
-            remote:  !     https://devguide.python.org/versions/#supported-versions
-            remote:  !     
-            remote:  !     Support for Python 3.8 will be removed from this buildpack on December 4th, 2024.
-            remote:  !     
-            remote:  !     Upgrade to a newer Python version as soon as possible to keep your app secure.
-            remote:  !     See: https://devcenter.heroku.com/articles/python-runtimes
-            remote:  !     
-            remote: -----> Installing python-#{LATEST_PYTHON_3_8}
-            remote: -----> Installing pip #{PIP_VERSION}, setuptools #{SETUPTOOLS_VERSION} and wheel #{WHEEL_VERSION}
-            remote: -----> Installing dependencies with Pipenv #{PIPENV_VERSION}
-            remote:        Installing dependencies from Pipfile.lock \\(.+\\)...
-            remote: -----> Installing SQLite3
-          REGEX
-        end
+          remote:  !     Make sure to include the '.' character at the start of the
+          remote:  !     filename. Don't add a file extension such as '.txt'.
+          remote:  !     
+          remote:  !     In the new file, specify your app's major Python version number
+          remote:  !     only. Don't include quotes or a 'python-' prefix.
+          remote:  !     
+          remote:  !     For example, to request the latest version of Python #{DEFAULT_PYTHON_MAJOR_VERSION},
+          remote:  !     update your .python-version file so it contains exactly:
+          remote:  !     #{DEFAULT_PYTHON_MAJOR_VERSION}
+          remote:  !     
+          remote:  !     We strongly recommend that you don't specify the Python patch
+          remote:  !     version number, since it will pin your app to an exact Python
+          remote:  !     version and so stop your app from receiving security updates
+          remote:  !     each time it builds.
+          remote:  !     
+          remote:  !     If your app already has a .python-version file, check that it:
+          remote:  !     
+          remote:  !     1. Is in the top level directory \\(not a subdirectory\\).
+          remote:  !     2. Is named exactly '.python-version' in all lowercase.
+          remote:  !     3. Isn't listed in '.gitignore' or '.slugignore'.
+          remote:  !     4. Has been added to the Git repository using 'git add --all'
+          remote:  !        and then committed using 'git commit'.
+          remote:  !     
+          remote:  !     In the future we will require the use of a .python-version
+          remote:  !     file and this warning will be made an error.
+          remote: 
+          remote: -----> Installing Python #{DEFAULT_PYTHON_FULL_VERSION}
+          remote: -----> Installing Pipenv #{PIPENV_VERSION}
+          remote: -----> Installing dependencies using 'pipenv install --deploy'
+          remote: -----> Saving cache
+        REGEX
       end
     end
-
-    context 'when using Heroku-22 or newer', stacks: %w[heroku-22 heroku-24] do
-      let(:allow_failure) { true }
-
-      # We only support Python 3.8 on Heroku-20 and older.
-      include_examples 'aborts the build with a runtime not available message (Pipenv)', LATEST_PYTHON_3_8
-    end
   end
 
-  context 'with a Pipfile.lock containing python_version 3.9' do
-    let(:allow_failure) { false }
-    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_python_3.9', allow_failure:) }
-
-    context 'when using Heroku-22 or older', stacks: %w[heroku-20 heroku-22] do
-      include_examples 'builds using Pipenv with the requested Python version', LATEST_PYTHON_3_9
-    end
-
-    context 'when using Heroku-24', stacks: %w[heroku-24] do
-      let(:allow_failure) { true }
+  context 'without a Pipfile.lock' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_no_lockfile', allow_failure: true) }
 
-      # We only support Python 3.9 on Heroku-22 and older.
-      include_examples 'aborts the build with a runtime not available message (Pipenv)', LATEST_PYTHON_3_9
+    it 'fails the build with an informative error message' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
+          remote: -----> Python app detected
+          remote: 
+          remote:  !     Error: No 'Pipfile.lock' found!
+          remote:  !     
+          remote:  !     A 'Pipfile' file was found, however, the associated 'Pipfile.lock'
+          remote:  !     Pipenv lockfile wasn't. This means your app dependency versions
+          remote:  !     aren't pinned, which means the package versions used on Heroku
+          remote:  !     might not match those installed in other environments.
+          remote:  !     
+          remote:  !     Using Pipenv in this way is unsafe and no longer supported.
+          remote:  !     
+          remote:  !     Run 'pipenv lock' locally to generate the lockfile, and make sure
+          remote:  !     that 'Pipfile.lock' isn't listed in '.gitignore' or '.slugignore'.
+          remote:  !     
+          remote:  !     Alternatively, if you wish to switch to another package manager,
+          remote:  !     delete your 'Pipfile' and then add either a 'requirements.txt',
+          remote:  !     'poetry.lock' or 'uv.lock' file.
+          remote:  !     
+          remote:  !     If you aren't sure which package manager to use, we recommend
+          remote:  !     trying uv, since it supports lockfiles, is extremely fast, and
+          remote:  !     is actively maintained by a full-time team:
+          remote:  !     https://docs.astral.sh/uv/
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        REGEX
+      end
     end
   end
 
-  context 'with a Pipfile.lock containing python_version 3.10' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_python_3.10') }
-
-    include_examples 'builds using Pipenv with the requested Python version', LATEST_PYTHON_3_10
-  end
-
-  context 'with a Pipfile.lock containing python_version 3.11' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_python_3.11') }
-
-    include_examples 'builds using Pipenv with the requested Python version', LATEST_PYTHON_3_11
-  end
-
-  context 'with a Pipfile.lock containing python_version 3.12' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_python_3.12') }
-
-    include_examples 'builds using Pipenv with the requested Python version', LATEST_PYTHON_3_12
-  end
-
-  context 'with a Pipfile.lock containing python_full_version 3.12.2' do
-    let(:allow_failure) { false }
-    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_python_full_version', allow_failure:) }
+  context 'with a Pipfile.lock containing invalid JSON' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_lockfile_invalid_json', allow_failure: true) }
 
-    it 'builds with the outdated Python version specified' do
+    it 'fails the build' do
       app.deploy do |app|
+        # The exact JQ error message varies between JQ versions, and thus across stacks.
         expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
           remote: -----> Python app detected
-          remote: -----> Using Python version specified in Pipfile.lock
+          remote: 
+          remote:  !     Error: Can't parse Pipfile.lock.
           remote:  !     
-          remote:  !     A Python security update is available! Upgrade as soon as possible to: python-#{LATEST_PYTHON_3_12}
-          remote:  !     See: https://devcenter.heroku.com/articles/python-runtimes
+          remote:  !     A Pipfile.lock file was found, however, it couldn't be parsed:
+          remote:  !     (jq: )?parse error: Invalid numeric literal at line 1, column 8
           remote:  !     
-          remote: -----> Installing python-3.12.2
-          remote: -----> Installing pip #{PIP_VERSION}, setuptools #{SETUPTOOLS_VERSION} and wheel #{WHEEL_VERSION}
-          remote: -----> Installing dependencies with Pipenv #{PIPENV_VERSION}
-          remote:        Installing dependencies from Pipfile.lock \\(.+\\)...
-          remote: -----> Installing SQLite3
+          remote:  !     This is likely due to it not being valid JSON.
+          remote:  !     
+          remote:  !     Run 'pipenv lock' to regenerate/fix the lockfile.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
         REGEX
       end
     end
   end
 
-  context 'with a Pipfile.lock containing an invalid python_version',
-          skip: 'unknown python_version values are currently ignored (W-8104668)' do
+  context 'with a Pipfile.lock containing an invalid python_version' do
     let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_python_version_invalid', allow_failure: true) }
 
     it 'fails the build' do
       app.deploy do |app|
         expect(clean_output(app.output)).to include(<<~OUTPUT)
           remote: -----> Python app detected
-          remote: -----> Using Python version specified in Pipfile.lock
+          remote: 
+          remote:  !     Error: Invalid Python version in Pipfile.lock.
+          remote:  !     
+          remote:  !     The Python version specified in your Pipfile.lock file by the
+          remote:  !     'python_version' or 'python_full_version' fields isn't valid.
+          remote:  !     
+          remote:  !     The following version was found:
+          remote:  !     ^3.12
+          remote:  !     
+          remote:  !     However, the Python version must be specified as either:
+          remote:  !     1. The major version only, for example: #{DEFAULT_PYTHON_MAJOR_VERSION} (recommended)
+          remote:  !     2. An exact patch version, for example: #{DEFAULT_PYTHON_MAJOR_VERSION}.999
           remote:  !     
-          remote:  !     Requested runtime '^3.12' is not available for this stack (#{app.stack}).
+          remote:  !     Wildcards aren't supported.
           remote:  !     
-          remote:  !     For a list of the supported Python versions, see:
-          remote:  !     https://devcenter.heroku.com/articles/python-support#supported-runtimes
+          remote:  !     Please update your Pipfile to use a valid Python version and
+          remote:  !     then run 'pipenv lock' to regenerate Pipfile.lock.
           remote:  !     
+          remote:  !     We strongly recommend that you don't specify the Python patch
+          remote:  !     version number, since it will pin your app to an exact Python
+          remote:  !     version and so stop your app from receiving security updates
+          remote:  !     each time it builds.
+          remote:  !     
+          remote:  !     For more information, see:
+          remote:  !     https://pipenv.pypa.io/en/stable/specifiers.html#specifying-versions-of-python
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
         OUTPUT
       end
     end
@@ -253,91 +393,91 @@
       app.deploy do |app|
         expect(clean_output(app.output)).to include(<<~OUTPUT)
           remote: -----> Python app detected
-          remote: -----> Using Python version specified in Pipfile.lock
+          remote: 
+          remote:  !     Error: Invalid Python version in Pipfile.lock.
+          remote:  !     
+          remote:  !     The Python version specified in your Pipfile.lock file by the
+          remote:  !     'python_version' or 'python_full_version' fields isn't valid.
+          remote:  !     
+          remote:  !     The following version was found:
+          remote:  !     3.9.*
+          remote:  !     
+          remote:  !     However, the Python version must be specified as either:
+          remote:  !     1. The major version only, for example: #{DEFAULT_PYTHON_MAJOR_VERSION} (recommended)
+          remote:  !     2. An exact patch version, for example: #{DEFAULT_PYTHON_MAJOR_VERSION}.999
           remote:  !     
-          remote:  !     Requested runtime 'python-X.Y.Z' is not available for this stack (#{app.stack}).
+          remote:  !     Wildcards aren't supported.
           remote:  !     
-          remote:  !     For a list of the supported Python versions, see:
-          remote:  !     https://devcenter.heroku.com/articles/python-support#supported-runtimes
+          remote:  !     Please update your Pipfile to use a valid Python version and
+          remote:  !     then run 'pipenv lock' to regenerate Pipfile.lock.
           remote:  !     
+          remote:  !     We strongly recommend that you don't specify the Python patch
+          remote:  !     version number, since it will pin your app to an exact Python
+          remote:  !     version and so stop your app from receiving security updates
+          remote:  !     each time it builds.
+          remote:  !     
+          remote:  !     For more information, see:
+          remote:  !     https://pipenv.pypa.io/en/stable/specifiers.html#specifying-versions-of-python
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
         OUTPUT
       end
     end
   end
 
-  context 'when there is a both a Pipfile.lock python_version and a runtime.txt' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_and_runtime_txt') }
+  context 'with a Pipfile.lock containing an EOL python_version' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_python_version_eol', allow_failure: true) }
 
-    it 'builds with the Python version from runtime.txt' do
+    it 'aborts the build with an EOL message' do
       app.deploy do |app|
-        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
+        expect(clean_output(app.output)).to match(Regexp.new(<<~OUTPUT))
           remote: -----> Python app detected
-          remote: -----> Using Python version specified in runtime.txt
-          remote: -----> Installing python-#{LATEST_PYTHON_3_12}
-          remote: -----> Installing pip #{PIP_VERSION}, setuptools #{SETUPTOOLS_VERSION} and wheel #{WHEEL_VERSION}
-          remote: -----> Installing dependencies with Pipenv #{PIPENV_VERSION}
-          remote:        Installing dependencies from Pipfile.lock \\(.+\\)...
-          remote: -----> Installing SQLite3
-        REGEX
+          remote: -----> Using Python 3.8 specified in Pipfile.lock
+          remote: 
+          remote:  !     Error: The requested Python version has reached end-of-life.
+          remote:  !     
+          remote:  !     Python 3.8 has reached its upstream end-of-life, and is
+          remote:  !     therefore no longer receiving security updates:
+          remote:  !     https://devguide.python.org/versions/#supported-versions
+          remote:  !     
+          remote:  !     As such, it's no longer supported by this buildpack:
+          remote:  !     https://devcenter.heroku.com/articles/python-support#supported-python-versions
+          remote:  !     
+          remote:  !     Please upgrade to at least Python 3.10 by changing the
+          remote:  !     version in your Pipfile.lock file.
+          remote:  !     
+          remote:  !     If possible, we recommend upgrading all the way to Python #{DEFAULT_PYTHON_MAJOR_VERSION},
+          remote:  !     since it contains many performance and usability improvements.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        OUTPUT
       end
     end
   end
 
-  context 'when Pipfile.lock is unchanged since the last build' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_python_version_unspecified') }
+  # TODO: Enable on Heroku-26 after the Pipenv and default Python versions next change,
+  # since for now there isn't a historic buildpack version we can use in this test whose
+  # stack check permits Heroku-26 and that also uses older Pipenv/Python versions.
+  context 'when the Pipenv and Python versions have changed since the last build', stacks: %w[heroku-22 heroku-24] do
+    let(:buildpacks) { ['https://github.com/heroku/heroku-buildpack-python#v313'] }
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_basic', buildpacks:) }
 
-    it 're-uses packages from the cache' do
+    it 'clears the cache before installing' do
       app.deploy do |app|
+        update_buildpacks(app, [:default])
+        FileUtils.rm('bin/post_compile')
         app.commit!
         app.push!
         expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
           remote: -----> Python app detected
-          remote: -----> No Python version was specified. Using the same version as the last build: python-#{DEFAULT_PYTHON_VERSION}
-          remote:        To use a different version, see: https://devcenter.heroku.com/articles/python-runtimes
-          remote: -----> Using cached install of python-#{DEFAULT_PYTHON_VERSION}
-          remote: -----> Installing pip #{PIP_VERSION}, setuptools #{SETUPTOOLS_VERSION} and wheel #{WHEEL_VERSION}
-          remote: -----> Installing dependencies with Pipenv #{PIPENV_VERSION}
-          remote:        Installing dependencies from Pipfile.lock \\(.+\\)...
-          remote: -----> Installing SQLite3
-          remote: -----> Discovering process types
-        REGEX
-      end
-    end
-  end
-
-  context 'when there is both a Pipfile.lock and a requirements.txt' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_and_requirements_txt') }
-
-    it 'builds with Pipenv rather than pip' do
-      app.deploy do |app|
-        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
-          remote: -----> Python app detected
-          remote: -----> Using Python version specified in Pipfile.lock
-          remote: -----> Installing python-#{LATEST_PYTHON_3_12}
-          remote: -----> Installing pip #{PIP_VERSION}, setuptools #{SETUPTOOLS_VERSION} and wheel #{WHEEL_VERSION}
-          remote: -----> Installing dependencies with Pipenv #{PIPENV_VERSION}
-          remote:        Installing dependencies from Pipfile.lock \\(.+\\)...
-          remote: -----> Installing SQLite3
-        REGEX
-      end
-    end
-  end
-
-  context 'when the Pipfile.lock is out of sync with Pipfile' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_lockfile_out_of_sync', allow_failure: true) }
-
-    it 'fails the build' do
-      app.deploy do |app|
-        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
-          remote: -----> Python app detected
-          remote: -----> No Python version was specified. Using the buildpack default: python-#{DEFAULT_PYTHON_VERSION}
-          remote:        To use a different version, see: https://devcenter.heroku.com/articles/python-runtimes
-          remote: -----> Installing python-#{DEFAULT_PYTHON_VERSION}
-          remote: -----> Installing pip #{PIP_VERSION}, setuptools #{SETUPTOOLS_VERSION} and wheel #{WHEEL_VERSION}
-          remote: -----> Installing dependencies with Pipenv #{PIPENV_VERSION}
-          remote:        Your Pipfile.lock \\(.+\\) is out of date.  Expected: \\(.+\\).
-          remote:        .+
-          remote:        ERROR:: Aborting deploy
+          remote: -----> Using Python 3.14 specified in Pipfile.lock
+          remote: -----> Discarding cache since:
+          remote:        - The Python version has changed from 3.14.0 to #{LATEST_PYTHON_3_14}
+          remote:        - The Pipenv version has changed from 2025.0.4 to #{PIPENV_VERSION}
+          remote: -----> Installing Python #{LATEST_PYTHON_3_14}
+          remote: -----> Installing Pipenv #{PIPENV_VERSION}
+          remote: -----> Installing dependencies using 'pipenv install --deploy'
+          remote: -----> Saving cache
         REGEX
       end
     end
@@ -347,68 +487,132 @@
     let(:buildpacks) { [:default, 'heroku-community/inline'] }
     let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_editable', buildpacks:) }
 
-    it 'rewrites .pth, .egg-link and finder paths correctly for hooks, later buildpacks, runtime and cached builds' do
+    it 'rewrites .pth and finder paths correctly for hooks, later buildpacks, runtime and cached builds' do
       app.deploy do |app|
         expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
-          remote: -----> Running post-compile hook
-          remote: easy-install.pth:/app/.heroku/src/gunicorn
-          remote: easy-install.pth:/tmp/build_.*/packages/local_package_setup_py
-          remote: __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.*/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
-          remote: gunicorn.egg-link:/app/.heroku/src/gunicorn
-          remote: local-package-setup-py.egg-link:/tmp/build_.*/packages/local_package_setup_py
-          remote: 
-          remote: Running entrypoint for the pyproject.toml-based local package: Hello pyproject.toml!
-          remote: Running entrypoint for the setup.py-based local package: Hello setup.py!
-          remote: Running entrypoint for the VCS package: gunicorn \\(version 20.1.0\\)
+          remote: -----> Installing dependencies using 'pipenv install --deploy'
+          remote: -----> Running bin/post_compile hook
+          remote:        __editable___gunicorn_23_0_0_finder.py:/app/.heroku/python/src/gunicorn/gunicorn'}
+          remote:        _editable_impl_pipenv_editable.pth:/tmp/build_.+
+          remote:        __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.+/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
+          remote:        __editable___local_package_setup_py_0_0_1_finder.py:/tmp/build_.+/packages/local_package_setup_py/local_package_setup_py'}
+          remote:        
+          remote:        Running entrypoint for the current package: Hello from pipenv-editable!
+          remote:        Running entrypoint for the pyproject.toml-based local package: Hello from pyproject.toml!
+          remote:        Running entrypoint for the setup.py-based local package: Hello from setup.py!
+          remote:        Running entrypoint for the VCS package: gunicorn \\(version 23.0.0\\)
+          remote: -----> Saving cache
+          .+
           remote: -----> Inline app detected
-          remote: easy-install.pth:/app/.heroku/src/gunicorn
-          remote: easy-install.pth:/tmp/build_.*/packages/local_package_setup_py
-          remote: __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.*/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
-          remote: gunicorn.egg-link:/app/.heroku/src/gunicorn
-          remote: local-package-setup-py.egg-link:/tmp/build_.*/packages/local_package_setup_py
+          remote: __editable___gunicorn_23_0_0_finder.py:/app/.heroku/python/src/gunicorn/gunicorn'}
+          remote: _editable_impl_pipenv_editable.pth:/tmp/build_.+
+          remote: __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.+/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
+          remote: __editable___local_package_setup_py_0_0_1_finder.py:/tmp/build_.+/packages/local_package_setup_py/local_package_setup_py'}
           remote: 
-          remote: Running entrypoint for the pyproject.toml-based local package: Hello pyproject.toml!
-          remote: Running entrypoint for the setup.py-based local package: Hello setup.py!
-          remote: Running entrypoint for the VCS package: gunicorn \\(version 20.1.0\\)
+          remote: Running entrypoint for the current package: Hello from pipenv-editable!
+          remote: Running entrypoint for the pyproject.toml-based local package: Hello from pyproject.toml!
+          remote: Running entrypoint for the setup.py-based local package: Hello from setup.py!
+          remote: Running entrypoint for the VCS package: gunicorn \\(version 23.0.0\\)
         REGEX
 
         # Test rewritten paths work at runtime.
-        expect(app.run('bin/test-entrypoints')).to include(<<~OUTPUT)
-          easy-install.pth:/app/.heroku/src/gunicorn
-          easy-install.pth:/app/packages/local_package_setup_py
+        expect(app.run('bin/test-entrypoints.sh')).to include(<<~OUTPUT)
+          __editable___gunicorn_23_0_0_finder.py:/app/.heroku/python/src/gunicorn/gunicorn'}
+          _editable_impl_pipenv_editable.pth:/app
           __editable___local_package_pyproject_toml_0_0_1_finder.py:/app/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
-          gunicorn.egg-link:/app/.heroku/src/gunicorn
-          local-package-setup-py.egg-link:/app/packages/local_package_setup_py
+          __editable___local_package_setup_py_0_0_1_finder.py:/app/packages/local_package_setup_py/local_package_setup_py'}
 
-          Running entrypoint for the pyproject.toml-based local package: Hello pyproject.toml!
-          Running entrypoint for the setup.py-based local package: Hello setup.py!
-          Running entrypoint for the VCS package: gunicorn (version 20.1.0)
+          Running entrypoint for the current package: Hello from pipenv-editable!
+          Running entrypoint for the pyproject.toml-based local package: Hello from pyproject.toml!
+          Running entrypoint for the setup.py-based local package: Hello from setup.py!
+          Running entrypoint for the VCS package: gunicorn (version 23.0.0)
         OUTPUT
 
         # Test that the cached .pth files work correctly.
         app.commit!
         app.push!
         expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
-          remote: -----> Running post-compile hook
-          remote: easy-install.pth:/app/.heroku/src/gunicorn
-          remote: easy-install.pth:/tmp/build_.*/packages/local_package_setup_py
-          remote: __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.*/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
-          remote: gunicorn.egg-link:/app/.heroku/src/gunicorn
-          remote: local-package-setup-py.egg-link:/tmp/build_.*/packages/local_package_setup_py
-          remote: 
-          remote: Running entrypoint for the pyproject.toml-based local package: Hello pyproject.toml!
-          remote: Running entrypoint for the setup.py-based local package: Hello setup.py!
-          remote: Running entrypoint for the VCS package: gunicorn \\(version 20.1.0\\)
+          remote: -----> Installing dependencies using 'pipenv install --deploy'
+          remote: -----> Running bin/post_compile hook
+          remote:        __editable___gunicorn_23_0_0_finder.py:/app/.heroku/python/src/gunicorn/gunicorn'}
+          remote:        _editable_impl_pipenv_editable.pth:/tmp/build_.+
+          remote:        __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.+/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
+          remote:        __editable___local_package_setup_py_0_0_1_finder.py:/tmp/build_.+/packages/local_package_setup_py/local_package_setup_py'}
+          remote:        
+          remote:        Running entrypoint for the current package: Hello from pipenv-editable!
+          remote:        Running entrypoint for the pyproject.toml-based local package: Hello from pyproject.toml!
+          remote:        Running entrypoint for the setup.py-based local package: Hello from setup.py!
+          remote:        Running entrypoint for the VCS package: gunicorn \\(version 23.0.0\\)
+          remote: -----> Saving cache
+          .+
           remote: -----> Inline app detected
-          remote: easy-install.pth:/app/.heroku/src/gunicorn
-          remote: easy-install.pth:/tmp/build_.*/packages/local_package_setup_py
-          remote: __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.*/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
-          remote: gunicorn.egg-link:/app/.heroku/src/gunicorn
-          remote: local-package-setup-py.egg-link:/tmp/build_.*/packages/local_package_setup_py
+          remote: __editable___gunicorn_23_0_0_finder.py:/app/.heroku/python/src/gunicorn/gunicorn'}
+          remote: _editable_impl_pipenv_editable.pth:/tmp/build_.+
+          remote: __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.+/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
+          remote: __editable___local_package_setup_py_0_0_1_finder.py:/tmp/build_.+/packages/local_package_setup_py/local_package_setup_py'}
+          remote: 
+          remote: Running entrypoint for the current package: Hello from pipenv-editable!
+          remote: Running entrypoint for the pyproject.toml-based local package: Hello from pyproject.toml!
+          remote: Running entrypoint for the setup.py-based local package: Hello from setup.py!
+          remote: Running entrypoint for the VCS package: gunicorn \\(version 23.0.0\\)
+        REGEX
+      end
+    end
+  end
+
+  # This tests that Pipenv doesn't fall back to system Python if the Python version in
+  # .python-version doesn't match that in Pipfile / Pipfile.lock. It also tests which of
+  # .python-version and Pipfile.lock take precedence for the installed Python version.
+  context 'when python_version in Pipfile.lock is incompatible with .python-version' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_mismatched_python_version', allow_failure: true) }
+
+    it 'fails the build', skip: 'https://github.com/pypa/pipenv/issues/6514' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Python app detected
+          remote: -----> Using Python #{LATEST_PYTHON_3_13} specified in .python-version
+          remote: -----> Installing Python #{LATEST_PYTHON_3_13}
+          remote: -----> Installing Pipenv #{PIPENV_VERSION}
+          remote: -----> Installing dependencies using 'pipenv install --deploy'
+          remote:        Warning: Your Pipfile requires "python_version" 3.12, but you are using #{LATEST_PYTHON_3_13} 
+          remote:        from //app/./python/bin/python3.
+          remote:        Usage: pipenv install [OPTIONS] [PACKAGES]...
+          remote:        
+          remote:        ERROR:: Aborting deploy
+          remote: 
+          remote:  !     Error: Unable to install dependencies using Pipenv.
+          remote:  !     
+          remote:  !     See the log output above for more information.
+        OUTPUT
+      end
+    end
+  end
+
+  # This tests not only our handling of failing dependency installation, but also that we're running
+  # Pipenv in such a way that it errors if the lockfile is out of sync, rather than simply updating it.
+  context 'when the Pipfile.lock is out of sync with Pipfile' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/pipenv_lockfile_out_of_sync', allow_failure: true) }
+
+    it 'fails the build' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
+          remote: -----> Python app detected
+          remote: -----> Using Python #{DEFAULT_PYTHON_MAJOR_VERSION} specified in .python-version
+          remote: -----> Installing Python #{DEFAULT_PYTHON_FULL_VERSION}
+          remote: -----> Installing Pipenv #{PIPENV_VERSION}
+          remote: -----> Installing dependencies using 'pipenv install --deploy'
+          remote:        Your Pipfile.lock 
+          remote:        \\(.+\\) is out of 
+          remote:        date. Expected: 
+          remote:        \\(.+\\).
+          remote:        .+
+          remote:        ERROR:: Aborting deploy
+          remote: 
+          remote:  !     Error: Unable to install dependencies using Pipenv.
+          remote:  !     
+          remote:  !     See the log output above for more information.
           remote: 
-          remote: Running entrypoint for the pyproject.toml-based local package: Hello pyproject.toml!
-          remote: Running entrypoint for the setup.py-based local package: Hello setup.py!
-          remote: Running entrypoint for the VCS package: gunicorn \\(version 20.1.0\\)
+          remote:  !     Push rejected, failed to compile Python app.
         REGEX
       end
     end
diff --git a/spec/hatchet/poetry_spec.rb b/spec/hatchet/poetry_spec.rb
new file mode 100644
index 000000000..03b980ddf
--- /dev/null
+++ b/spec/hatchet/poetry_spec.rb
@@ -0,0 +1,360 @@
+# frozen_string_literal: true
+
+require_relative '../spec_helper'
+
+RSpec.describe 'Poetry support' do
+  context 'with a poetry.lock' do
+    let(:buildpacks) { [:default, 'heroku-community/inline'] }
+    let(:app) { Hatchet::Runner.new('spec/fixtures/poetry_basic', buildpacks:) }
+
+    it 'installs successfully using Poetry and on rebuilds uses the cache' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
+          remote: -----> Python app detected
+          remote: -----> Using Python #{DEFAULT_PYTHON_MAJOR_VERSION} specified in .python-version
+          remote: -----> Installing Python #{DEFAULT_PYTHON_FULL_VERSION}
+          remote: -----> Installing Poetry #{POETRY_VERSION}
+          remote: -----> Installing dependencies using 'poetry sync --only main'
+          remote:        Installing dependencies from lock file
+          remote:        
+          remote:        Package operations: 1 install, 0 updates, 0 removals
+          remote:        
+          remote:          - Installing typing-extensions \\(4.15.0\\)
+          remote: -----> Running bin/post_compile hook
+          remote:        BUILD_DIR=/tmp/build_.+
+          remote:        CACHE_DIR=/tmp/codon/tmp/cache
+          remote:        C_INCLUDE_PATH=/app/.heroku/python/include
+          remote:        CPLUS_INCLUDE_PATH=/app/.heroku/python/include
+          remote:        ENV_DIR=/tmp/.+
+          remote:        LANG=en_US.UTF-8
+          remote:        LD_LIBRARY_PATH=/app/.heroku/python/lib
+          remote:        LIBRARY_PATH=/app/.heroku/python/lib
+          remote:        PATH=/tmp/codon/tmp/cache/.heroku/python-poetry/bin:/app/.heroku/python/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+          remote:        PKG_CONFIG_PATH=/app/.heroku/python/lib/pkg-config
+          remote:        POETRY_VIRTUALENVS_CREATE=false
+          remote:        POETRY_VIRTUALENVS_USE_POETRY_PYTHON=true
+          remote:        PYTHONUNBUFFERED=1
+          remote: -----> Saving cache
+          remote: 
+          remote:  !     Note: We recently added support for the package manager uv:
+          remote:  !     https://devcenter.heroku.com/changelog-items/3238
+          remote:  !     
+          remote:  !     It's now our recommended Python package manager, since it
+          remote:  !     supports lockfiles, is faster, gives more helpful error
+          remote:  !     messages, and is actively maintained by a full-time team.
+          remote:  !     
+          remote:  !     If you haven't tried it yet, we suggest you take a look!
+          remote:  !     https://docs.astral.sh/uv/
+          remote: 
+          remote: -----> Inline app detected
+          remote: LANG=en_US.UTF-8
+          remote: LD_LIBRARY_PATH=/app/.heroku/python/lib
+          remote: LIBRARY_PATH=/app/.heroku/python/lib
+          remote: PATH=/app/.heroku/python/bin:/tmp/codon/tmp/cache/.heroku/python-poetry/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+          remote: POETRY_VIRTUALENVS_CREATE=false
+          remote: POETRY_VIRTUALENVS_USE_POETRY_PYTHON=true
+          remote: PYTHONHOME=/app/.heroku/python
+          remote: PYTHONPATH=/app
+          remote: PYTHONUNBUFFERED=true
+          remote: 
+          remote: \\['',
+          remote:  '/app',
+          remote:  '/app/.heroku/python/lib/python314.zip',
+          remote:  '/app/.heroku/python/lib/python3.14',
+          remote:  '/app/.heroku/python/lib/python3.14/lib-dynload',
+          remote:  '/app/.heroku/python/lib/python3.14/site-packages'\\]
+          remote: 
+          remote: Poetry \\(version #{POETRY_VERSION}\\)
+          remote: Skipping virtualenv creation, as specified in config file.
+          remote: typing-extensions 4.15.0 Backported and Experimental Type Hints for Python ...
+          remote: 
+          remote: <module 'typing_extensions' from '/app/.heroku/python/lib/python3.14/site-packages/typing_extensions.py'>
+          remote: 
+          remote: \\{
+          remote:   "cache_restore_duration": [0-9.]+,
+          remote:   "cache_save_duration": [0-9.]+,
+          remote:   "cache_status": "empty",
+          remote:   "dependencies_install_duration": [0-9.]+,
+          remote:   "django_collectstatic_duration": [0-9.]+,
+          remote:   "nltk_downloader_duration": [0-9.]+,
+          remote:   "package_manager": "poetry",
+          remote:   "package_manager_install_duration": [0-9.]+,
+          remote:   "poetry_version": "#{POETRY_VERSION}",
+          remote:   "post_compile_hook": true,
+          remote:   "post_compile_hook_duration": [0-9.]+,
+          remote:   "pre_compile_hook": false,
+          remote:   "python_install_duration": [0-9.]+,
+          remote:   "python_version": "#{DEFAULT_PYTHON_FULL_VERSION}",
+          remote:   "python_version_major": "3.14",
+          remote:   "python_version_origin": ".python-version",
+          remote:   "python_version_outdated": false,
+          remote:   "python_version_pinned": false,
+          remote:   "python_version_requested": "3.14",
+          remote:   "total_duration": [0-9.]+
+          remote: \\}
+        REGEX
+
+        app.commit!
+        app.push!
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
+          remote: -----> Python app detected
+          remote: -----> Using Python #{DEFAULT_PYTHON_MAJOR_VERSION} specified in .python-version
+          remote: -----> Restoring cache
+          remote: -----> Using cached install of Python #{DEFAULT_PYTHON_FULL_VERSION}
+          remote: -----> Using cached Poetry #{POETRY_VERSION}
+          remote: -----> Installing dependencies using 'poetry sync --only main'
+          remote:        Installing dependencies from lock file
+          remote:        
+          remote:        No dependencies to install or update
+          remote: -----> Running bin/post_compile hook
+          remote:        .+
+          remote: -----> Saving cache
+        REGEX
+
+        command = 'bin/print-env-vars.sh && if command -v poetry; then echo "Poetry unexpectedly found!" && exit 1; fi'
+        expect(normalize_trailing_newlines(app.run(command))).to eq(<<~OUTPUT)
+          DYNO_RAM=512
+          FORWARDED_ALLOW_IPS=*
+          GUNICORN_CMD_ARGS=--access-logfile -
+          LANG=en_US.UTF-8
+          LD_LIBRARY_PATH=/app/.heroku/python/lib
+          LIBRARY_PATH=/app/.heroku/python/lib
+          PATH=/app/.heroku/python/bin:/usr/local/bin:/usr/bin:/bin
+          PYTHONHOME=/app/.heroku/python
+          PYTHONPATH=/app
+          PYTHONUNBUFFERED=true
+          WEB_CONCURRENCY=2
+          WEB_CONCURRENCY_SET_BY=heroku/python
+        OUTPUT
+        expect($CHILD_STATUS.exitstatus).to eq(0)
+      end
+    end
+  end
+
+  # TODO: Enable on Heroku-26 after the Poetry and default Python versions next change,
+  # since for now there isn't a historic buildpack version we can use in this test whose
+  # stack check permits Heroku-26 and that also uses older Poetry/Python versions.
+  context 'when the Poetry and Python versions have changed since the last build', stacks: %w[heroku-22 heroku-24] do
+    let(:buildpacks) { ['https://github.com/heroku/heroku-buildpack-python#v313'] }
+    let(:app) { Hatchet::Runner.new('spec/fixtures/poetry_basic', buildpacks:) }
+
+    it 'clears the cache before installing' do
+      app.deploy do |app|
+        update_buildpacks(app, [:default])
+        FileUtils.rm('bin/post_compile')
+        app.commit!
+        app.push!
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Python app detected
+          remote: -----> Using Python 3.14 specified in .python-version
+          remote: -----> Discarding cache since:
+          remote:        - The Python version has changed from 3.14.0 to #{LATEST_PYTHON_3_14}
+          remote:        - The Poetry version has changed from 2.2.1 to #{POETRY_VERSION}
+          remote: -----> Installing Python #{LATEST_PYTHON_3_14}
+          remote: -----> Installing Poetry #{POETRY_VERSION}
+          remote: -----> Installing dependencies using 'poetry sync --only main'
+          remote:        Installing dependencies from lock file
+          remote:        
+          remote:        Package operations: 1 install, 0 updates, 0 removals
+          remote:        
+          remote:          - Installing typing-extensions (4.15.0)
+          remote: -----> Saving cache
+        OUTPUT
+      end
+    end
+  end
+
+  context 'when poetry.lock contains editable requirements (both VCS and local package)' do
+    let(:buildpacks) { [:default, 'heroku-community/inline'] }
+    let(:app) { Hatchet::Runner.new('spec/fixtures/poetry_editable', buildpacks:) }
+
+    it 'rewrites .pth and finder paths correctly for hooks, later buildpacks, runtime and cached builds' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
+          remote: -----> Installing dependencies using 'poetry sync --only main'
+          remote:        Installing dependencies from lock file
+          remote:        
+          remote:        Package operations: 4 installs, 0 updates, 0 removals
+          remote:        
+          remote:          - Installing packaging \\(25.0\\)
+          remote:          - Installing gunicorn \\(23.0.0 56b5ad8\\)
+          remote:          - Installing local-package-pyproject-toml \\(0.0.1 /tmp/build_.+/packages/local_package_pyproject_toml\\)
+          remote:          - Installing local-package-setup-py \\(0.0.1 /tmp/build_.+/packages/local_package_setup_py\\)
+          remote:        
+          remote:        Installing the current project: poetry-editable \\(0.0.1\\)
+          remote: -----> Running bin/post_compile hook
+          remote:        __editable___gunicorn_23_0_0_finder.py:/app/.heroku/python/src/gunicorn/gunicorn'}
+          remote:        __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.+/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
+          remote:        __editable___local_package_setup_py_0_0_1_finder.py:/tmp/build_.+/packages/local_package_setup_py/local_package_setup_py'}
+          remote:        poetry_editable.pth:/tmp/build_.+
+          remote:        
+          remote:        Running entrypoint for the current package: Hello from poetry-editable!
+          remote:        Running entrypoint for the pyproject.toml-based local package: Hello from pyproject.toml!
+          remote:        Running entrypoint for the setup.py-based local package: Hello from setup.py!
+          remote:        Running entrypoint for the VCS package: gunicorn \\(version 23.0.0\\)
+          remote: -----> Saving cache
+          .+
+          remote: -----> Inline app detected
+          remote: __editable___gunicorn_23_0_0_finder.py:/app/.heroku/python/src/gunicorn/gunicorn'}
+          remote: __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.+/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
+          remote: __editable___local_package_setup_py_0_0_1_finder.py:/tmp/build_.+/packages/local_package_setup_py/local_package_setup_py'}
+          remote: poetry_editable.pth:/tmp/build_.+
+          remote: 
+          remote: Running entrypoint for the current package: Hello from poetry-editable!
+          remote: Running entrypoint for the pyproject.toml-based local package: Hello from pyproject.toml!
+          remote: Running entrypoint for the setup.py-based local package: Hello from setup.py!
+          remote: Running entrypoint for the VCS package: gunicorn \\(version 23.0.0\\)
+        REGEX
+
+        # Test rewritten paths work at runtime.
+        expect(app.run('bin/test-entrypoints.sh')).to include(<<~OUTPUT)
+          __editable___gunicorn_23_0_0_finder.py:/app/.heroku/python/src/gunicorn/gunicorn'}
+          __editable___local_package_pyproject_toml_0_0_1_finder.py:/app/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
+          __editable___local_package_setup_py_0_0_1_finder.py:/app/packages/local_package_setup_py/local_package_setup_py'}
+          poetry_editable.pth:/app
+
+          Running entrypoint for the current package: Hello from poetry-editable!
+          Running entrypoint for the pyproject.toml-based local package: Hello from pyproject.toml!
+          Running entrypoint for the setup.py-based local package: Hello from setup.py!
+          Running entrypoint for the VCS package: gunicorn (version 23.0.0)
+        OUTPUT
+
+        # Test that the cached .pth files work correctly.
+        app.commit!
+        app.push!
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
+          remote: -----> Installing dependencies using 'poetry sync --only main'
+          remote:        Installing dependencies from lock file
+          remote:        
+          remote:        Package operations: 0 installs, 3 updates, 0 removals
+          remote:        
+          remote:          - Updating gunicorn \\(23.0.0 /app/.heroku/python/src/gunicorn -> 23.0.0 56b5ad8\\)
+          remote:          - Updating local-package-pyproject-toml \\(0.0.1 /tmp/build_.+/packages/local_package_pyproject_toml -> 0.0.1 /tmp/build_.+/packages/local_package_pyproject_toml\\)
+          remote:          - Updating local-package-setup-py \\(0.0.1 /tmp/build_.+/packages/local_package_setup_py -> 0.0.1 /tmp/build_.+/packages/local_package_setup_py\\)
+          remote:        
+          remote:        Installing the current project: poetry-editable \\(0.0.1\\)
+          remote: -----> Running bin/post_compile hook
+          remote:        __editable___gunicorn_23_0_0_finder.py:/app/.heroku/python/src/gunicorn/gunicorn'}
+          remote:        __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.+/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
+          remote:        __editable___local_package_setup_py_0_0_1_finder.py:/tmp/build_.+/packages/local_package_setup_py/local_package_setup_py'}
+          remote:        poetry_editable.pth:/tmp/build_.+
+          remote:        
+          remote:        Running entrypoint for the current package: Hello from poetry-editable!
+          remote:        Running entrypoint for the pyproject.toml-based local package: Hello from pyproject.toml!
+          remote:        Running entrypoint for the setup.py-based local package: Hello from setup.py!
+          remote:        Running entrypoint for the VCS package: gunicorn \\(version 23.0.0\\)
+          remote: -----> Saving cache
+          .+
+          remote: -----> Inline app detected
+          remote: __editable___gunicorn_23_0_0_finder.py:/app/.heroku/python/src/gunicorn/gunicorn'}
+          remote: __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.+/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
+          remote: __editable___local_package_setup_py_0_0_1_finder.py:/tmp/build_.+/packages/local_package_setup_py/local_package_setup_py'}
+          remote: poetry_editable.pth:/tmp/build_.+
+          remote: 
+          remote: Running entrypoint for the current package: Hello from poetry-editable!
+          remote: Running entrypoint for the pyproject.toml-based local package: Hello from pyproject.toml!
+          remote: Running entrypoint for the setup.py-based local package: Hello from setup.py!
+          remote: Running entrypoint for the VCS package: gunicorn \\(version 23.0.0\\)
+        REGEX
+      end
+    end
+  end
+
+  # This checks that the Poetry bootstrap works even with older bundled pip, and that our
+  # chosen Poetry version also supports our oldest supported Python version. The fixture
+  # also includes a `brotli` directory to test the workaround for an `ensurepip` bug in
+  # older Python versions: https://github.com/heroku/heroku-buildpack-python/issues/1697
+  context 'when using our oldest supported Python version' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/poetry_oldest_python') }
+
+    it 'installs successfully' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Python app detected
+          remote: -----> Using Python 3.10.0 specified in .python-version
+          remote: 
+          remote:  !     Warning: Support for Python 3.10 is deprecated!
+          remote:  !     
+          remote:  !     Python 3.10 will reach its upstream end-of-life in October 2026,
+          remote:  !     at which point it will no longer receive security updates:
+          remote:  !     https://devguide.python.org/versions/#supported-versions
+          remote:  !     
+          remote:  !     As such, support for Python 3.10 will be removed from this
+          remote:  !     buildpack on 6th January 2027.
+          remote:  !     
+          remote:  !     Upgrade to a newer Python version as soon as possible, by
+          remote:  !     changing the version in your .python-version file.
+          remote:  !     
+          remote:  !     For more information, see:
+          remote:  !     https://devcenter.heroku.com/articles/python-support#supported-python-versions
+          remote: 
+          remote: 
+          remote:  !     Warning: A Python patch update is available!
+          remote:  !     
+          remote:  !     Your app is using Python 3.10.0, however, there is a newer
+          remote:  !     patch release of Python 3.10 available: #{LATEST_PYTHON_3_10}
+          remote:  !     
+          remote:  !     It is important to always use the latest patch version of
+          remote:  !     Python to keep your app secure.
+          remote:  !     
+          remote:  !     Update your .python-version file to use the new version.
+          remote:  !     
+          remote:  !     We strongly recommend that you don't pin your app to an
+          remote:  !     exact Python version such as 3.10.0, and instead only specify
+          remote:  !     the major Python version of 3.10 in your .python-version file.
+          remote:  !     This will allow your app to receive the latest available Python
+          remote:  !     patch version automatically and prevent this warning.
+          remote: 
+          remote: -----> Installing Python 3.10.0
+          remote: -----> Installing Poetry #{POETRY_VERSION}
+          remote: -----> Installing dependencies using 'poetry sync --only main'
+          remote:        Installing dependencies from lock file
+          remote:        
+          remote:        Package operations: 1 install, 0 updates, 0 removals
+          remote:        
+          remote:          - Installing typing-extensions (4.15.0)
+          remote: -----> Saving cache
+        OUTPUT
+      end
+    end
+  end
+
+  # This is disabled since it's currently broken upstream: https://github.com/python-poetry/poetry/issues/10226
+  # This tests that Poetry doesn't download its own Python or fall back to system Python
+  # if the Python version in pyproject.toml doesn't match that in .python-version.
+  # context 'when requires-python in pyproject.toml is incompatible with .python-version' do
+  #   let(:app) { Hatchet::Runner.new('spec/fixtures/poetry_mismatched_python_version', allow_failure: true) }
+  #
+  #   it 'fails the build' do
+  #     app.deploy do |app|
+  #       expect(clean_output(app.output)).to include(<<~OUTPUT)
+  #         remote: -----> Installing dependencies using 'poetry sync --only main'
+  #         remote:        <TODO whatever error message Poetry displays if they fix their bug>
+  #       OUTPUT
+  #     end
+  #   end
+  # end
+
+  # This tests not only our handling of failing dependency installation, but also that we're running
+  # Poetry in such a way that it errors if the lockfile is out of sync, rather than simply updating it.
+  context 'when poetry.lock is out of sync with pyproject.toml' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/poetry_lockfile_out_of_sync', allow_failure: true) }
+
+    it 'fails the build' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Installing dependencies using 'poetry sync --only main'
+          remote:        Installing dependencies from lock file
+          remote:        
+          remote:        pyproject.toml changed significantly since poetry.lock was last generated. Run `poetry lock` to fix the lock file.
+          remote: 
+          remote:  !     Error: Unable to install dependencies using Poetry.
+          remote:  !     
+          remote:  !     See the log output above for more information.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        OUTPUT
+      end
+    end
+  end
+end
diff --git a/spec/hatchet/profile_d_scripts_spec.rb b/spec/hatchet/profile_d_scripts_spec.rb
index 434d6ccad..20b90418f 100644
--- a/spec/hatchet/profile_d_scripts_spec.rb
+++ b/spec/hatchet/profile_d_scripts_spec.rb
@@ -5,61 +5,37 @@
 RSpec.describe '.profile.d/ scripts' do
   it 'sets the required run-time env vars' do
     Hatchet::Runner.new('spec/fixtures/procfile', run_multi: true).deploy do |app|
-      # These are written as a single test to reduce end to end test time. This repo uses parallel_split_test,
-      # so we can't perform app setup in a `before(:all)` and have multiple tests run against the single app.
-
-      list_envs_cmd = 'env | sort | grep -vE "^(_|DYNO|PORT|PS1|SHLVL|TERM)="'
-
-      # Check all env vars are set correctly when there are no user-provided env vars.
-      # Also checks that the WEB_CONCURRENCY related log output is not shown for one-off dynos.
-      app.run_multi(list_envs_cmd) do |output, _|
-        expect(output).to eq(<<~OUTPUT)
-          DYNO_RAM=512
-          FORWARDED_ALLOW_IPS=*
-          GUNICORN_CMD_ARGS=--access-logfile -
-          HOME=/app
-          LANG=en_US.UTF-8
-          LD_LIBRARY_PATH=/app/.heroku/vendor/lib:/app/.heroku/python/lib:
-          LIBRARY_PATH=/app/.heroku/vendor/lib:/app/.heroku/python/lib:
-          PATH=/app/.heroku/python/bin:/usr/local/bin:/usr/bin:/bin
-          PWD=/app
-          PYTHONHASHSEED=random
-          PYTHONHOME=/app/.heroku/python
-          PYTHONPATH=/app
-          PYTHONUNBUFFERED=true
-          WEB_CONCURRENCY=2
-        OUTPUT
-      end
+      # These are written as a single test to reduce end to end test time. (This repo uses parallel_split_test,
+      # so we can't perform app setup in a `before(:all)` and have multiple tests run against the single app.)
+      # These tests supplement the run-time env var tests performed for each package manager, so intentionally
+      # don't duplicate those.
 
       # Check user-provided env var values are preserved/overridden as appropriate.
       # Also checks that the WEB_CONCURRENCY related log output is not shown for worker dynos.
+      list_envs_cmd = 'printenv | sort | grep -vE "^(_|DYNO|HOME|PORT|PS1|PWD|SHLVL|TERM)="'
       user_env_vars = [
         'DYNO_RAM=this-should-be-overridden',
         'FORWARDED_ALLOW_IPS=this-should-be-overridden',
         'GUNICORN_CMD_ARGS=this-should-be-preserved',
-        'HOME=this-should-be-overridden',
         'LANG=this-should-be-overridden',
         'LD_LIBRARY_PATH=/this-should-be-preserved',
         'LIBRARY_PATH=/this-should-be-preserved',
         'PATH=/this-should-be-preserved:/usr/local/bin:/usr/bin:/bin',
-        'PYTHONHASHSEED=this-should-be-preserved',
         'PYTHONHOME=/this-should-be-overridden',
         'PYTHONPATH=/this-should-be-preserved',
         'PYTHONUNBUFFERED=this-should-be-overridden',
         'WEB_CONCURRENCY=this-should-be-preserved',
       ]
       app.run_multi(list_envs_cmd, heroku: { env: user_env_vars.join(';'), type: 'example-worker' }) do |output, _|
-        expect(output).to eq(<<~OUTPUT)
+        expect(normalize_trailing_newlines(output)).to eq(<<~OUTPUT)
           DYNO_RAM=512
           FORWARDED_ALLOW_IPS=*
           GUNICORN_CMD_ARGS=this-should-be-preserved
-          HOME=/app
           LANG=C.UTF-8
-          LD_LIBRARY_PATH=/app/.heroku/vendor/lib:/app/.heroku/python/lib:/this-should-be-preserved
-          LIBRARY_PATH=/app/.heroku/vendor/lib:/app/.heroku/python/lib:/this-should-be-preserved
+          LD_LIBRARY_PATH=/app/.heroku/python/lib:/this-should-be-preserved
+          LIBRARY_PATH=/app/.heroku/python/lib:/this-should-be-preserved
           PATH=/app/.heroku/python/bin:/this-should-be-preserved:/usr/local/bin:/usr/bin:/bin
-          PWD=/app
-          PYTHONHASHSEED=this-should-be-preserved
+          PIP_DISABLE_PIP_VERSION_CHECK=1
           PYTHONHOME=/app/.heroku/python
           PYTHONPATH=/this-should-be-preserved
           PYTHONUNBUFFERED=true
@@ -67,82 +43,89 @@
         OUTPUT
       end
 
-      list_concurrency_envs_cmd = 'env | sort | grep -E "^(DYNO_RAM|WEB_CONCURRENCY)="'
+      list_concurrency_envs_cmd = 'printenv | sort | grep -E "^(DYNO_RAM|WEB_CONCURRENCY.*)="'
 
       # Check WEB_CONCURRENCY support when using a Standard-1X dyno.
       # We set the process type to `web` so that we can test the web-dyno-only log output.
       app.run_multi(list_concurrency_envs_cmd, heroku: { size: 'standard-1x', type: 'web' }) do |output, _|
-        expect(output).to eq(<<~OUTPUT)
+        expect(normalize_trailing_newlines(output)).to eq(<<~OUTPUT)
           Python buildpack: Detected 512 MB available memory and 8 CPU cores.
           Python buildpack: Defaulting WEB_CONCURRENCY to 2 based on the available memory.
           DYNO_RAM=512
           WEB_CONCURRENCY=2
+          WEB_CONCURRENCY_SET_BY=heroku/python
         OUTPUT
       end
 
       # Standard-2X
       app.run_multi(list_concurrency_envs_cmd, heroku: { size: 'standard-2x', type: 'web' }) do |output, _|
-        expect(output).to eq(<<~OUTPUT)
+        expect(normalize_trailing_newlines(output)).to eq(<<~OUTPUT)
           Python buildpack: Detected 1024 MB available memory and 8 CPU cores.
           Python buildpack: Defaulting WEB_CONCURRENCY to 4 based on the available memory.
           DYNO_RAM=1024
           WEB_CONCURRENCY=4
+          WEB_CONCURRENCY_SET_BY=heroku/python
         OUTPUT
       end
 
       # Performance-M
       app.run_multi(list_concurrency_envs_cmd, heroku: { size: 'performance-m', type: 'web' }) do |output, _|
-        expect(output).to eq(<<~OUTPUT)
+        expect(normalize_trailing_newlines(output)).to eq(<<~OUTPUT)
           Python buildpack: Detected 2560 MB available memory and 2 CPU cores.
           Python buildpack: Defaulting WEB_CONCURRENCY to 5 based on the number of CPU cores.
           DYNO_RAM=2560
           WEB_CONCURRENCY=5
+          WEB_CONCURRENCY_SET_BY=heroku/python
         OUTPUT
       end
 
       # Performance-L
       app.run_multi(list_concurrency_envs_cmd, heroku: { size: 'performance-l', type: 'web' }) do |output, _|
-        expect(output).to eq(<<~OUTPUT)
+        expect(normalize_trailing_newlines(output)).to eq(<<~OUTPUT)
           Python buildpack: Detected 14336 MB available memory and 8 CPU cores.
           Python buildpack: Defaulting WEB_CONCURRENCY to 17 based on the number of CPU cores.
           DYNO_RAM=14336
           WEB_CONCURRENCY=17
+          WEB_CONCURRENCY_SET_BY=heroku/python
         OUTPUT
       end
 
       # Performance-L-RAM
       app.run_multi(list_concurrency_envs_cmd, heroku: { size: 'performance-l-ram', type: 'web' }) do |output, _|
-        expect(output).to eq(<<~OUTPUT)
+        expect(normalize_trailing_newlines(output)).to eq(<<~OUTPUT)
           Python buildpack: Detected 30720 MB available memory and 4 CPU cores.
           Python buildpack: Defaulting WEB_CONCURRENCY to 9 based on the number of CPU cores.
           DYNO_RAM=30720
           WEB_CONCURRENCY=9
+          WEB_CONCURRENCY_SET_BY=heroku/python
         OUTPUT
       end
 
       # Performance-XL
       app.run_multi(list_concurrency_envs_cmd, heroku: { size: 'performance-xl', type: 'web' }) do |output, _|
-        expect(output).to eq(<<~OUTPUT)
+        expect(normalize_trailing_newlines(output)).to eq(<<~OUTPUT)
           Python buildpack: Detected 63488 MB available memory and 8 CPU cores.
           Python buildpack: Defaulting WEB_CONCURRENCY to 17 based on the number of CPU cores.
           DYNO_RAM=63488
           WEB_CONCURRENCY=17
+          WEB_CONCURRENCY_SET_BY=heroku/python
         OUTPUT
       end
 
       # Performance-2XL
       app.run_multi(list_concurrency_envs_cmd, heroku: { size: 'performance-2xl', type: 'web' }) do |output, _|
-        expect(output).to eq(<<~OUTPUT)
+        expect(normalize_trailing_newlines(output)).to eq(<<~OUTPUT)
           Python buildpack: Detected 129024 MB available memory and 16 CPU cores.
           Python buildpack: Defaulting WEB_CONCURRENCY to 33 based on the number of CPU cores.
           DYNO_RAM=129024
           WEB_CONCURRENCY=33
+          WEB_CONCURRENCY_SET_BY=heroku/python
         OUTPUT
       end
 
       # Check that WEB_CONCURRENCY is preserved if set, but that we still set DYNO_RAM.
       app.run_multi(list_concurrency_envs_cmd, heroku: { env: 'WEB_CONCURRENCY=999', type: 'web' }) do |output, _|
-        expect(output).to eq(<<~OUTPUT)
+        expect(normalize_trailing_newlines(output)).to eq(<<~OUTPUT)
           Python buildpack: Detected 512 MB available memory and 8 CPU cores.
           Python buildpack: Skipping automatic configuration of WEB_CONCURRENCY since it's already set.
           DYNO_RAM=512
diff --git a/spec/hatchet/python_update_warning_spec.rb b/spec/hatchet/python_update_warning_spec.rb
deleted file mode 100644
index 6c7f66d62..000000000
--- a/spec/hatchet/python_update_warning_spec.rb
+++ /dev/null
@@ -1,113 +0,0 @@
-# frozen_string_literal: true
-
-require_relative '../spec_helper'
-
-RSpec.shared_examples 'warns there is a Python update available' do |requested_version, latest_version|
-  it 'warns there is a Python update available' do
-    app.deploy do |app|
-      expect(clean_output(app.output)).to include(<<~OUTPUT)
-        remote: -----> Python app detected
-        remote: -----> Using Python version specified in runtime.txt
-        remote:  !     
-        remote:  !     A Python security update is available! Upgrade as soon as possible to: python-#{latest_version}
-        remote:  !     See: https://devcenter.heroku.com/articles/python-runtimes
-        remote:  !     
-        remote: -----> Installing python-#{requested_version}
-      OUTPUT
-    end
-  end
-end
-
-RSpec.shared_examples 'aborts the build without showing an update warning' do |requested_version|
-  it 'aborts the build without showing an update warning' do
-    app.deploy do |app|
-      expect(clean_output(app.output)).to include(<<~OUTPUT)
-        remote: -----> Python app detected
-        remote: -----> Using Python version specified in runtime.txt
-        remote:  !     
-        remote:  !     Requested runtime 'python-#{requested_version}' is not available for this stack (#{app.stack}).
-        remote:  !     
-        remote:  !     For a list of the supported Python versions, see:
-        remote:  !     https://devcenter.heroku.com/articles/python-support#supported-runtimes
-        remote:  !     
-      OUTPUT
-    end
-  end
-end
-
-RSpec.describe 'Python update warnings' do
-  context 'with a runtime.txt containing python-3.8.12' do
-    let(:allow_failure) { false }
-    let(:app) { Hatchet::Runner.new('spec/fixtures/python_3.8_outdated', allow_failure:) }
-
-    context 'when using Heroku-20', stacks: %w[heroku-20] do
-      it 'warns about both the deprecated major version and the patch update' do
-        app.deploy do |app|
-          expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
-            remote: -----> Python app detected
-            remote: -----> Using Python version specified in runtime.txt
-            remote:  !     
-            remote:  !     Python 3.8 will reach its upstream end-of-life in October 2024, at which
-            remote:  !     point it will no longer receive security updates:
-            remote:  !     https://devguide.python.org/versions/#supported-versions
-            remote:  !     
-            remote:  !     Support for Python 3.8 will be removed from this buildpack on December 4th, 2024.
-            remote:  !     
-            remote:  !     Upgrade to a newer Python version as soon as possible to keep your app secure.
-            remote:  !     See: https://devcenter.heroku.com/articles/python-runtimes
-            remote:  !     
-            remote:  !     
-            remote:  !     A Python security update is available! Upgrade as soon as possible to: python-#{LATEST_PYTHON_3_8}
-            remote:  !     See: https://devcenter.heroku.com/articles/python-runtimes
-            remote:  !     
-            remote: -----> Installing python-3.8.12
-          REGEX
-        end
-      end
-    end
-
-    context 'when using Heroku-22 or newer', stacks: %w[heroku-22 heroku-24] do
-      let(:allow_failure) { true }
-
-      # We only support Python 3.8 on Heroku-20 and older.
-      include_examples 'aborts the build without showing an update warning', '3.8.12'
-    end
-  end
-
-  context 'with a runtime.txt containing python-3.9.12' do
-    let(:allow_failure) { false }
-    let(:app) { Hatchet::Runner.new('spec/fixtures/python_3.9_outdated', allow_failure:) }
-
-    context 'when using Heroku-22 or older', stacks: %w[heroku-20 heroku-22] do
-      include_examples 'warns there is a Python update available', '3.9.12', LATEST_PYTHON_3_9
-    end
-
-    context 'when using Heroku-24', stacks: %w[heroku-24] do
-      let(:allow_failure) { true }
-
-      # We only support Python 3.9 on Heroku-22 and older.
-      include_examples 'aborts the build without showing an update warning', '3.9.12'
-    end
-  end
-
-  context 'with a runtime.txt containing python-3.10.5' do
-    let(:allow_failure) { false }
-    let(:app) { Hatchet::Runner.new('spec/fixtures/python_3.10_outdated', allow_failure:) }
-
-    include_examples 'warns there is a Python update available', '3.10.5', LATEST_PYTHON_3_10
-  end
-
-  context 'with a runtime.txt containing python-3.11.0' do
-    let(:allow_failure) { false }
-    let(:app) { Hatchet::Runner.new('spec/fixtures/python_3.11_outdated', allow_failure:) }
-
-    include_examples 'warns there is a Python update available', '3.11.0', LATEST_PYTHON_3_11
-  end
-
-  context 'with a runtime.txt containing python-3.12.0' do
-    let(:allow_failure) { false }
-    let(:app) { Hatchet::Runner.new('spec/fixtures/python_3.12_outdated', allow_failure:) }
-
-    include_examples 'warns there is a Python update available', '3.12.0', LATEST_PYTHON_3_12
-  end
-end
diff --git a/spec/hatchet/python_version_spec.rb b/spec/hatchet/python_version_spec.rb
index 7ae02287b..24a083e04 100644
--- a/spec/hatchet/python_version_spec.rb
+++ b/spec/hatchet/python_version_spec.rb
@@ -2,36 +2,30 @@
 
 require_relative '../spec_helper'
 
-RSpec.shared_examples 'builds with the requested Python version' do |python_version|
-  it "builds with Python #{python_version}" do
+RSpec.shared_examples 'builds with the requested Python version' do |requested_version, resolved_version|
+  it "builds with Python #{requested_version}" do
     app.deploy do |app|
-      expect(clean_output(app.output)).to include(<<~OUTPUT)
-        remote: -----> Python app detected
-        remote: -----> Using Python version specified in runtime.txt
-        remote: -----> Installing python-#{python_version}
-        remote: -----> Installing pip #{PIP_VERSION}, setuptools #{SETUPTOOLS_VERSION} and wheel #{WHEEL_VERSION}
-        remote: -----> Installing SQLite3
-        remote: -----> Installing requirements with pip
-        remote:        Collecting urllib3 (from -r requirements.txt (line 1))
-      OUTPUT
-      expect(app.run('python -V')).to include("Python #{python_version}")
-    end
-  end
-end
-
-RSpec.shared_examples 'aborts the build with a runtime not available message' do |requested_runtime|
-  it 'aborts the build with a runtime not available message' do
-    app.deploy do |app|
-      expect(clean_output(app.output)).to include(<<~OUTPUT)
-        remote: -----> Python app detected
-        remote: -----> Using Python version specified in runtime.txt
-        remote:  !     
-        remote:  !     Requested runtime '#{requested_runtime}' is not available for this stack (#{app.stack}).
-        remote:  !     
-        remote:  !     For a list of the supported Python versions, see:
-        remote:  !     https://devcenter.heroku.com/articles/python-support#supported-runtimes
-        remote:  !     
-      OUTPUT
+      if ['3.10', '3.11', '3.12'].include?(requested_version)
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Python app detected
+          remote: -----> Using Python #{requested_version} specified in .python-version
+          remote: -----> Installing Python #{resolved_version}
+          remote: -----> Installing pip #{PIP_VERSION} and setuptools #{SETUPTOOLS_VERSION}
+          remote: -----> Installing dependencies using 'pip install -r requirements.txt'
+          remote:        Collecting typing-extensions==4.15.0 (from -r requirements.txt (line 2))
+        OUTPUT
+      else
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Python app detected
+          remote: -----> Using Python #{requested_version} specified in .python-version
+          remote: -----> Installing Python #{resolved_version}
+          remote: -----> Installing pip #{PIP_VERSION}
+          remote: -----> Installing dependencies using 'pip install -r requirements.txt'
+          remote:        Collecting typing-extensions==4.15.0 (from -r requirements.txt (line 2))
+        OUTPUT
+      end
+      expect(normalize_trailing_newlines(app.run('python -V'))).to eq("Python #{resolved_version}\n")
+      expect($CHILD_STATUS.exitstatus).to eq(0)
     end
   end
 end
@@ -46,9 +40,49 @@
         app.deploy do |app|
           expect(clean_output(app.output)).to include(<<~OUTPUT)
             remote: -----> Python app detected
-            remote: -----> No Python version was specified. Using the buildpack default: python-#{DEFAULT_PYTHON_VERSION}
-            remote:        To use a different version, see: https://devcenter.heroku.com/articles/python-runtimes
-            remote: -----> Installing python-#{DEFAULT_PYTHON_VERSION}
+            remote: -----> No Python version was specified. Using the buildpack default: Python #{DEFAULT_PYTHON_MAJOR_VERSION}
+            remote: 
+            remote:  !     Warning: No Python version was specified.
+            remote:  !     
+            remote:  !     Your app doesn't specify a Python version and so the buildpack
+            remote:  !     picked a default version for you.
+            remote:  !     
+            remote:  !     Relying on this default version isn't recommended, since it
+            remote:  !     can change over time and may not be consistent with your local
+            remote:  !     development environment, CI or other instances of your app.
+            remote:  !     
+            remote:  !     Please configure an explicit Python version for your app.
+            remote:  !     
+            remote:  !     Create a new file in the root directory of your app named:
+            remote:  !     .python-version
+            remote:  !     
+            remote:  !     Make sure to include the '.' character at the start of the
+            remote:  !     filename. Don't add a file extension such as '.txt'.
+            remote:  !     
+            remote:  !     In the new file, specify your app's major Python version number
+            remote:  !     only. Don't include quotes or a 'python-' prefix.
+            remote:  !     
+            remote:  !     For example, to request the latest version of Python #{DEFAULT_PYTHON_MAJOR_VERSION},
+            remote:  !     update your .python-version file so it contains exactly:
+            remote:  !     #{DEFAULT_PYTHON_MAJOR_VERSION}
+            remote:  !     
+            remote:  !     We strongly recommend that you don't specify the Python patch
+            remote:  !     version number, since it will pin your app to an exact Python
+            remote:  !     version and so stop your app from receiving security updates
+            remote:  !     each time it builds.
+            remote:  !     
+            remote:  !     If your app already has a .python-version file, check that it:
+            remote:  !     
+            remote:  !     1. Is in the top level directory (not a subdirectory).
+            remote:  !     2. Is named exactly '.python-version' in all lowercase.
+            remote:  !     3. Isn't listed in '.gitignore' or '.slugignore'.
+            remote:  !     4. Has been added to the Git repository using 'git add --all'
+            remote:  !        and then committed using 'git commit'.
+            remote:  !     
+            remote:  !     In the future we will require the use of a .python-version
+            remote:  !     file and this warning will be made an error.
+            remote: 
+            remote: -----> Installing Python #{DEFAULT_PYTHON_FULL_VERSION}
           OUTPUT
         end
       end
@@ -56,186 +90,647 @@
 
     context 'with an app last built using an older default Python version' do
       # This test performs an initial build using an older buildpack version, followed
-      # by a build using the current version. This ensures that the current buildpack
-      # can successfully read the version metadata written to the build cache in the past.
-      let(:buildpacks) { ['https://github.com/heroku/heroku-buildpack-python#v250'] }
+      # by a build using the current version. This ensures that:
+      # - The current buildpack can successfully read the version metadata
+      #   written to the build cache by older buildpack versions.
+      # - If no Python version is specified, the same major version as the
+      #   last build is used (sticky major versioning).
+      # - Changes in the pip version are handled correctly.
+      let(:buildpacks) { ['https://github.com/heroku/heroku-buildpack-python#v342'] }
 
-      it 'builds with the same Python version as the last build' do
+      it 'builds with the same major Python version as the last build' do
         app.deploy do |app|
           update_buildpacks(app, [:default])
           app.commit!
           app.push!
           expect(clean_output(app.output)).to include(<<~OUTPUT)
             remote: -----> Python app detected
-            remote: -----> No Python version was specified. Using the same version as the last build: python-3.12.3
-            remote:        To use a different version, see: https://devcenter.heroku.com/articles/python-runtimes
+            remote: -----> No Python version was specified. Using the same major version as the last build: Python 3.14
+            remote: 
+            remote:  !     Warning: No Python version was specified.
+            remote:  !     
+            remote:  !     Your app doesn't specify a Python version and so the buildpack
+            remote:  !     picked a default version for you.
+            remote:  !     
+            remote:  !     Relying on this default version isn't recommended, since it
+            remote:  !     can change over time and may not be consistent with your local
+            remote:  !     development environment, CI or other instances of your app.
+            remote:  !     
+            remote:  !     Please configure an explicit Python version for your app.
+            remote:  !     
+            remote:  !     Create a new file in the root directory of your app named:
+            remote:  !     .python-version
+            remote:  !     
+            remote:  !     Make sure to include the '.' character at the start of the
+            remote:  !     filename. Don't add a file extension such as '.txt'.
+            remote:  !     
+            remote:  !     In the new file, specify your app's major Python version number
+            remote:  !     only. Don't include quotes or a 'python-' prefix.
             remote:  !     
-            remote:  !     A Python security update is available! Upgrade as soon as possible to: python-#{LATEST_PYTHON_3_12}
-            remote:  !     See: https://devcenter.heroku.com/articles/python-runtimes
+            remote:  !     For example, to request the latest version of Python 3.14,
+            remote:  !     update your .python-version file so it contains exactly:
+            remote:  !     3.14
             remote:  !     
-            remote: -----> No change in requirements detected, installing from cache
-            remote: -----> Using cached install of python-3.12.3
+            remote:  !     We strongly recommend that you don't specify the Python patch
+            remote:  !     version number, since it will pin your app to an exact Python
+            remote:  !     version and so stop your app from receiving security updates
+            remote:  !     each time it builds.
+            remote:  !     
+            remote:  !     If your app already has a .python-version file, check that it:
+            remote:  !     
+            remote:  !     1. Is in the top level directory (not a subdirectory).
+            remote:  !     2. Is named exactly '.python-version' in all lowercase.
+            remote:  !     3. Isn't listed in '.gitignore' or '.slugignore'.
+            remote:  !     4. Has been added to the Git repository using 'git add --all'
+            remote:  !        and then committed using 'git commit'.
+            remote:  !     
+            remote:  !     In the future we will require the use of a .python-version
+            remote:  !     file and this warning will be made an error.
+            remote: 
+            remote: -----> Discarding cache since:
+            remote:        - The Python version has changed from 3.14.4 to #{LATEST_PYTHON_3_14}
+            remote:        - The pip version has changed from 26.0.1 to #{PIP_VERSION}
+            remote: -----> Installing Python #{LATEST_PYTHON_3_14}
+            remote: -----> Installing pip #{PIP_VERSION}
+          OUTPUT
+          expect(normalize_trailing_newlines(app.run('python -V'))).to eq("Python #{LATEST_PYTHON_3_14}\n")
+          expect($CHILD_STATUS.exitstatus).to eq(0)
+        end
+      end
+    end
+
+    context 'with an app last built using an EOL Python version' do
+      # This fixture emulates the cache from a previous build that used a now-EOL Python version.
+      let(:app) { Hatchet::Runner.new('spec/fixtures/python_version_eol_cached', allow_failure: true) }
+
+      it 'aborts the build with an EOL message' do
+        app.deploy do |app|
+          expect(clean_output(app.output)).to include(<<~OUTPUT)
+            remote: -----> Python app detected
+            remote: -----> Running bin/pre_compile hook
+            remote: -----> No Python version was specified. Using the same major version as the last build: Python 3.9
+            remote: 
+            remote:  !     Error: The cached Python version has reached end-of-life.
+            remote:  !     
+            remote:  !     Your app doesn't specify a Python version, and so normally
+            remote:  !     would use the version cached from the last build (3.9).
+            remote:  !     
+            remote:  !     However, Python 3.9 has reached its upstream end-of-life,
+            remote:  !     and is therefore no longer receiving security updates:
+            remote:  !     https://devguide.python.org/versions/#supported-versions
+            remote:  !     
+            remote:  !     As such, it's no longer supported by this buildpack:
+            remote:  !     https://devcenter.heroku.com/articles/python-support#supported-python-versions
+            remote:  !     
+            remote:  !     Please upgrade to at least Python 3.10 by configuring an
+            remote:  !     explicit Python version for your app.
+            remote:  !     
+            remote:  !     Create a new file in the root directory of your app named:
+            remote:  !     .python-version
+            remote:  !     
+            remote:  !     Make sure to include the '.' character at the start of the
+            remote:  !     filename. Don't add a file extension such as '.txt'.
+            remote:  !     
+            remote:  !     In the new file, specify your app's major Python version number
+            remote:  !     only. Don't include quotes or a 'python-' prefix.
+            remote:  !     
+            remote:  !     For example, to request the latest version of Python 3.10,
+            remote:  !     update your .python-version file so it contains exactly:
+            remote:  !     3.10
+            remote:  !     
+            remote:  !     We strongly recommend that you don't specify the Python patch
+            remote:  !     version number, since it will pin your app to an exact Python
+            remote:  !     version and so stop your app from receiving security updates
+            remote:  !     each time it builds.
+            remote: 
+            remote:  !     Push rejected, failed to compile Python app.
+          OUTPUT
+        end
+      end
+    end
+
+    context 'with an app last built using an unrecognised Python version' do
+      # This fixture emulates the cache from a previous build which used a newer default
+      # Python version than the version supported by this buildpack version.
+      let(:app) { Hatchet::Runner.new('spec/fixtures/python_version_non_existent_major_cached', allow_failure: true) }
+
+      it 'aborts the build with an unrecognised Python version message' do
+        app.deploy do |app|
+          expect(clean_output(app.output)).to include(<<~OUTPUT)
+            remote: -----> Python app detected
+            remote: -----> Running bin/pre_compile hook
+            remote: -----> No Python version was specified. Using the same major version as the last build: Python 3.99
+            remote: 
+            remote:  !     Error: The cached Python version isn't recognised.
+            remote:  !     
+            remote:  !     Your app doesn't specify a Python version, and so normally
+            remote:  !     would use the version cached from the last build (3.99).
+            remote:  !     
+            remote:  !     However, Python 3.99 isn't recognised by this version
+            remote:  !     of the buildpack.
+            remote:  !     
+            remote:  !     This can occur if you have downgraded the version of the
+            remote:  !     buildpack to an older version.
+            remote:  !     
+            remote:  !     Please switch back to a newer version of this buildpack:
+            remote:  !     https://devcenter.heroku.com/articles/managing-buildpacks#view-your-buildpacks
+            remote:  !     https://devcenter.heroku.com/articles/managing-buildpacks#classic-buildpacks-references
+            remote:  !     
+            remote:  !     Alternatively, request an older Python version by creating
+            remote:  !     a .python-version file in the root directory of your app,
+            remote:  !     that contains a Python version like:
+            remote:  !     3.14
+            remote: 
+            remote:  !     Push rejected, failed to compile Python app.
           OUTPUT
-          expect(app.run('python -V')).to include('Python 3.12.3')
         end
       end
     end
   end
 
-  context 'when runtime.txt contains python-3.6.15' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/python_3.6', allow_failure: true) }
+  context 'when .python-version contains Python 3.10' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/python_3.10') }
 
-    it 'aborts the build with an EOL message' do
+    it 'builds with Python 3.10 but shows a deprecation warning' do
       app.deploy do |app|
         expect(clean_output(app.output)).to include(<<~OUTPUT)
           remote: -----> Python app detected
-          remote: -----> Using Python version specified in runtime.txt
+          remote: -----> Using Python 3.10 specified in .python-version
+          remote: 
+          remote:  !     Warning: Support for Python 3.10 is deprecated!
           remote:  !     
-          remote:  !     Python 3.6 reached upstream end-of-life on December 23rd, 2021, and is
-          remote:  !     therefore no longer receiving security updates:
+          remote:  !     Python 3.10 will reach its upstream end-of-life in October 2026,
+          remote:  !     at which point it will no longer receive security updates:
           remote:  !     https://devguide.python.org/versions/#supported-versions
           remote:  !     
-          remote:  !     As such, it is no longer supported by this buildpack.
+          remote:  !     As such, support for Python 3.10 will be removed from this
+          remote:  !     buildpack on 6th January 2027.
+          remote:  !     
+          remote:  !     Upgrade to a newer Python version as soon as possible, by
+          remote:  !     changing the version in your .python-version file.
+          remote:  !     
+          remote:  !     For more information, see:
+          remote:  !     https://devcenter.heroku.com/articles/python-support#supported-python-versions
+          remote: 
+          remote: -----> Installing Python #{LATEST_PYTHON_3_10}
+          remote: -----> Installing pip #{PIP_VERSION} and setuptools #{SETUPTOOLS_VERSION}
+          remote: -----> Installing dependencies using 'pip install -r requirements.txt'
+          remote:        Collecting typing-extensions==4.15.0 (from -r requirements.txt (line 2))
+        OUTPUT
+        expect(normalize_trailing_newlines(app.run('python -V'))).to eq("Python #{LATEST_PYTHON_3_10}\n")
+        expect($CHILD_STATUS.exitstatus).to eq(0)
+      end
+    end
+  end
+
+  context 'when .python-version contains Python 3.11' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/python_3.11') }
+
+    it_behaves_like 'builds with the requested Python version', '3.11', LATEST_PYTHON_3_11
+  end
+
+  context 'when .python-version contains Python 3.12' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/python_3.12') }
+
+    it_behaves_like 'builds with the requested Python version', '3.12', LATEST_PYTHON_3_12
+  end
+
+  context 'when .python-version contains Python 3.13' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/python_3.13') }
+
+    it_behaves_like 'builds with the requested Python version', '3.13', LATEST_PYTHON_3_13
+  end
+
+  context 'when .python-version contains Python 3.14' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/python_3.14') }
+
+    it_behaves_like 'builds with the requested Python version', '3.14', LATEST_PYTHON_3_14
+  end
+
+  context 'when .python-version is misspelled' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/python_version_file_misspelled', allow_failure: true) }
+
+    it 'aborts the build with a misspelled .python-version file message' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Python app detected
+          remote: 
+          remote:  !     Error: Your .python-version file is spelled incorrectly.
           remote:  !     
-          remote:  !     Please upgrade to a newer Python version.
+          remote:  !     Your app's .python-version file currently has the filename:
+          remote:  !     '.python-version '
           remote:  !     
-          remote:  !     For a list of the supported Python versions, see:
-          remote:  !     https://devcenter.heroku.com/articles/python-support#supported-runtimes
+          remote:  !     However, the correct spelling is (without quotes):
+          remote:  !     '.python-version'
           remote:  !     
+          remote:  !     You must rename your file to the correct name.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
         OUTPUT
       end
     end
   end
 
-  context 'when runtime.txt contains python-3.7.17' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/python_3.7', allow_failure: true) }
+  context 'when .python-version contains an invalid Python version string' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/python_version_file_invalid_version', allow_failure: true) }
 
-    it 'aborts the build with an EOL message' do
+    it 'aborts the build with an invalid Python version message' do
       app.deploy do |app|
         expect(clean_output(app.output)).to include(<<~OUTPUT)
           remote: -----> Python app detected
-          remote: -----> Using Python version specified in runtime.txt
+          remote: 
+          remote:  !     Error: Invalid Python version in .python-version.
           remote:  !     
-          remote:  !     Python 3.7 reached upstream end-of-life on June 27th, 2023, and is
-          remote:  !     therefore no longer receiving security updates:
-          remote:  !     https://devguide.python.org/versions/#supported-versions
+          remote:  !     The Python version specified in your .python-version file
+          remote:  !     isn't in the correct format.
           remote:  !     
-          remote:  !     As such, it is no longer supported by this buildpack.
+          remote:  !     The following version was found:
+          remote:  !     ���python -	��3.12.0�[0m
           remote:  !     
-          remote:  !     Please upgrade to a newer Python version.
+          remote:  !     However, the Python version must be specified as either:
+          remote:  !     1. The major version only, for example: #{DEFAULT_PYTHON_MAJOR_VERSION} (recommended)
+          remote:  !     2. An exact patch version, for example: #{DEFAULT_PYTHON_MAJOR_VERSION}.999
           remote:  !     
-          remote:  !     For a list of the supported Python versions, see:
-          remote:  !     https://devcenter.heroku.com/articles/python-support#supported-runtimes
+          remote:  !     Don't include quotes, a 'python-' prefix or wildcards. Any
+          remote:  !     code comments must be on a separate line prefixed with '#'.
           remote:  !     
+          remote:  !     For example, to request the latest version of Python #{DEFAULT_PYTHON_MAJOR_VERSION},
+          remote:  !     update your .python-version file so it contains exactly:
+          remote:  !     #{DEFAULT_PYTHON_MAJOR_VERSION}
+          remote:  !     
+          remote:  !     We strongly recommend that you don't specify the Python patch
+          remote:  !     version number, since it will pin your app to an exact Python
+          remote:  !     version and so stop your app from receiving security updates
+          remote:  !     each time it builds.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
         OUTPUT
       end
     end
   end
 
-  context 'when runtime.txt contains python-3.8.19' do
-    let(:allow_failure) { false }
-    let(:app) { Hatchet::Runner.new('spec/fixtures/python_3.8', allow_failure:) }
+  context 'when .python-version is saved using an unsupported file encoding' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/python_version_file_unsupported_encoding', allow_failure: true) }
 
-    context 'when using Heroku-20', stacks: %w[heroku-20] do
-      it 'builds with Python 3.8.19 but shows a deprecation warning' do
-        app.deploy do |app|
-          expect(clean_output(app.output)).to include(<<~OUTPUT)
-            remote: -----> Python app detected
-            remote: -----> Using Python version specified in runtime.txt
-            remote:  !     
-            remote:  !     Python 3.8 will reach its upstream end-of-life in October 2024, at which
-            remote:  !     point it will no longer receive security updates:
-            remote:  !     https://devguide.python.org/versions/#supported-versions
-            remote:  !     
-            remote:  !     Support for Python 3.8 will be removed from this buildpack on December 4th, 2024.
-            remote:  !     
-            remote:  !     Upgrade to a newer Python version as soon as possible to keep your app secure.
-            remote:  !     See: https://devcenter.heroku.com/articles/python-runtimes
-            remote:  !     
-            remote: -----> Installing python-#{LATEST_PYTHON_3_8}
-            remote: -----> Installing pip #{PIP_VERSION}, setuptools #{SETUPTOOLS_VERSION} and wheel #{WHEEL_VERSION}
-            remote: -----> Installing SQLite3
-            remote: -----> Installing requirements with pip
-            remote:        Collecting urllib3 (from -r requirements.txt (line 1))
-          OUTPUT
-          expect(app.run('python -V')).to include("Python #{LATEST_PYTHON_3_8}")
-        end
+    it 'aborts the build with an invalid file encoding message' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Python app detected
+          remote: 
+          remote:  !     Error: Unable to read .python-version.
+          remote:  !     
+          remote:  !     Your .python-version file couldn't be read because it's using
+          remote:  !     an unsupported text encoding:
+          remote:  !     Unicode text, UTF-8 (with BOM) text, with CRLF line terminators
+          remote:  !     
+          remote:  !     Configure your editor to save files as UTF-8, without a BOM,
+          remote:  !     then delete and recreate the file using the correct encoding.
+          remote:  !     
+          remote:  !     If that doesn't work, make sure you don't have a .gitattributes
+          remote:  !     file that's overriding the text encoding.
+          remote:  !     
+          remote:  !     Note: On Windows, if you pipe or redirect output to a file
+          remote:  !     it can result in the file being encoded in UTF-16 LE when
+          remote:  !     using certain terminals and Windows settings. We recommend
+          remote:  !     you create the file using a text editor instead.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        OUTPUT
       end
     end
+  end
 
-    context 'when using Heroku-22 or newer', stacks: %w[heroku-22 heroku-24] do
-      let(:allow_failure) { true }
+  context 'when .python-version does not contain a Python version' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/python_version_file_no_version', allow_failure: true) }
 
-      # We only support Python 3.8 on Heroku-20 and older.
-      include_examples 'aborts the build with a runtime not available message', "python-#{LATEST_PYTHON_3_8}"
+    it 'aborts the build with a no version string found message' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Python app detected
+          remote: 
+          remote:  !     Error: No Python version found in .python-version.
+          remote:  !     
+          remote:  !     No Python version was found in your .python-version file.
+          remote:  !     
+          remote:  !     Update the file so that it contains your app's major Python
+          remote:  !     version number. Don't include quotes or a 'python-' prefix.
+          remote:  !     
+          remote:  !     For example, to request the latest version of Python #{DEFAULT_PYTHON_MAJOR_VERSION},
+          remote:  !     update your .python-version file so it contains exactly:
+          remote:  !     #{DEFAULT_PYTHON_MAJOR_VERSION}
+          remote:  !     
+          remote:  !     If the file already contains a version, check the line doesn't
+          remote:  !     begin with a '#', otherwise it will be treated as a comment.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        OUTPUT
+      end
     end
   end
 
-  context 'when runtime.txt contains python-3.9.19' do
-    let(:allow_failure) { false }
-    let(:app) { Hatchet::Runner.new('spec/fixtures/python_3.9', allow_failure:) }
+  context 'when .python-version contains multiple Python versions' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/python_version_file_multiple_versions', allow_failure: true) }
 
-    context 'when using Heroku-22 or older', stacks: %w[heroku-20 heroku-22] do
-      include_examples 'builds with the requested Python version', LATEST_PYTHON_3_9
+    it 'aborts the build with a multiple versions not supported message' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Python app detected
+          remote: 
+          remote:  !     Error: Multiple Python versions found in .python-version.
+          remote:  !     
+          remote:  !     Multiple versions were found in your .python-version file:
+          remote:  !     
+          remote:  !     3.12
+          remote:  !     2.7
+          remote:  !     
+          remote:  !     Update the file so it contains only one Python version.
+          remote:  !     
+          remote:  !     For example, to request the latest version of Python #{DEFAULT_PYTHON_MAJOR_VERSION},
+          remote:  !     update your .python-version file so it contains exactly:
+          remote:  !     #{DEFAULT_PYTHON_MAJOR_VERSION}
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        OUTPUT
+      end
     end
+  end
 
-    context 'when using Heroku-24', stacks: %w[heroku-24] do
-      let(:allow_failure) { true }
+  context 'when .python-version contains an EOL Python 3.x version' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/python_version_eol', allow_failure: true) }
 
-      # We only support Python 3.9 on Heroku-22 and older.
-      include_examples 'aborts the build with a runtime not available message', "python-#{LATEST_PYTHON_3_9}"
+    it 'aborts the build with an EOL message' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Python app detected
+          remote: -----> Using Python 3.9 specified in .python-version
+          remote: 
+          remote:  !     Error: The requested Python version has reached end-of-life.
+          remote:  !     
+          remote:  !     Python 3.9 has reached its upstream end-of-life, and is
+          remote:  !     therefore no longer receiving security updates:
+          remote:  !     https://devguide.python.org/versions/#supported-versions
+          remote:  !     
+          remote:  !     As such, it's no longer supported by this buildpack:
+          remote:  !     https://devcenter.heroku.com/articles/python-support#supported-python-versions
+          remote:  !     
+          remote:  !     Please upgrade to at least Python 3.10 by changing the
+          remote:  !     version in your .python-version file.
+          remote:  !     
+          remote:  !     If possible, we recommend upgrading all the way to Python #{DEFAULT_PYTHON_MAJOR_VERSION},
+          remote:  !     since it contains many performance and usability improvements.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        OUTPUT
+      end
     end
   end
 
-  context 'when runtime.txt contains python-3.10.14' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/python_3.10') }
+  context 'when .python-version contains a non-existent Python major version' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/python_version_non_existent_major', allow_failure: true) }
 
-    include_examples 'builds with the requested Python version', LATEST_PYTHON_3_10
+    it 'aborts the build with an unrecognised Python version message' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Python app detected
+          remote: -----> Using Python 3.999 specified in .python-version
+          remote: 
+          remote:  !     Error: The requested Python version isn't recognised.
+          remote:  !     
+          remote:  !     The requested Python version 3.999 isn't recognised.
+          remote:  !     
+          remote:  !     Check that this Python version has been officially released,
+          remote:  !     and that the Python buildpack has added support for it:
+          remote:  !     https://devguide.python.org/versions/#supported-versions
+          remote:  !     https://devcenter.heroku.com/articles/python-support#supported-python-versions
+          remote:  !     
+          remote:  !     If it has, make sure that you are using the latest version
+          remote:  !     of this buildpack, and haven't pinned to an older release:
+          remote:  !     https://devcenter.heroku.com/articles/managing-buildpacks#view-your-buildpacks
+          remote:  !     https://devcenter.heroku.com/articles/managing-buildpacks#classic-buildpacks-references
+          remote:  !     
+          remote:  !     Otherwise, switch to a supported version (such as Python 3.14)
+          remote:  !     by changing the version in your .python-version file.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        OUTPUT
+      end
+    end
   end
 
-  context 'when runtime.txt contains python-3.11.9' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/python_3.11') }
+  context 'when .python-version contains a non-existent Python patch version' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/python_version_non_existent_patch', allow_failure: true) }
 
-    include_examples 'builds with the requested Python version', LATEST_PYTHON_3_11
+    it 'aborts the build with a version not available message' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
+          remote: -----> Python app detected
+          remote: -----> Using Python 3.12.999 specified in .python-version
+          remote: -----> Installing Python 3.12.999
+          remote:        curl: \\(22\\) The requested URL returned error: .+
+          remote:        zstd: /\\*stdin\\*\\\\: unexpected end of file 
+          remote:        tar: Child returned status 1
+          remote:        tar: Error is not recoverable: exiting now
+          remote: 
+          remote:  !     Error: The requested Python version isn't available.
+          remote:  !     
+          remote:  !     Your app's .python-version file specifies a Python version
+          remote:  !     of 3.12.999, however, we couldn't find that version on S3.
+          remote:  !     
+          remote:  !     Check that this Python version has been released upstream,
+          remote:  !     and that the Python buildpack has added support for it:
+          remote:  !     https://www.python.org/downloads/
+          remote:  !     https://github.com/heroku/heroku-buildpack-python/blob/main/CHANGELOG.md
+          remote:  !     
+          remote:  !     If it has, make sure that you are using the latest version
+          remote:  !     of this buildpack, and haven't pinned to an older release:
+          remote:  !     https://devcenter.heroku.com/articles/managing-buildpacks#view-your-buildpacks
+          remote:  !     https://devcenter.heroku.com/articles/managing-buildpacks#classic-buildpacks-references
+          remote:  !     
+          remote:  !     We also strongly recommend that you don't pin your app to an
+          remote:  !     exact Python version such as 3.12.999, and instead only specify
+          remote:  !     the major Python version of 3.12 in your .python-version file.
+          remote:  !     This will allow your app to receive the latest available Python
+          remote:  !     patch version automatically, and prevent this type of error.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        REGEX
+      end
+    end
   end
 
-  context 'when runtime.txt contains python-3.12.4' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/python_3.12') }
+  context 'when .python-version contains an outdated Python patch version' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/python_version_outdated') }
 
-    include_examples 'builds with the requested Python version', LATEST_PYTHON_3_12
+    it 'warns there is a Python update available' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Python app detected
+          remote: -----> Using Python 3.14.0 specified in .python-version
+          remote: 
+          remote:  !     Warning: A Python patch update is available!
+          remote:  !     
+          remote:  !     Your app is using Python 3.14.0, however, there is a newer
+          remote:  !     patch release of Python 3.14 available: #{LATEST_PYTHON_3_14}
+          remote:  !     
+          remote:  !     It is important to always use the latest patch version of
+          remote:  !     Python to keep your app secure.
+          remote:  !     
+          remote:  !     Update your .python-version file to use the new version.
+          remote:  !     
+          remote:  !     We strongly recommend that you don't pin your app to an
+          remote:  !     exact Python version such as 3.14.0, and instead only specify
+          remote:  !     the major Python version of 3.14 in your .python-version file.
+          remote:  !     This will allow your app to receive the latest available Python
+          remote:  !     patch version automatically and prevent this warning.
+          remote: 
+          remote: -----> Installing Python 3.14.0
+          remote: -----> Installing pip #{PIP_VERSION}
+        OUTPUT
+      end
+    end
+  end
+
+  context 'when runtime.txt contains an invalid Python version string' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/runtime_txt_invalid_version', allow_failure: true) }
+
+    it 'aborts the build with an invalid runtime.txt message' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Python app detected
+          remote: 
+          remote:  !     Error: Invalid Python version in runtime.txt.
+          remote:  !     
+          remote:  !     The Python version specified in your runtime.txt file isn't
+          remote:  !     in the correct format.
+          remote:  !     
+          remote:  !     However, the runtime.txt file is deprecated since it has been
+          remote:  !     replaced by the more widely supported .python-version file:
+          remote:  !     https://devcenter.heroku.com/changelog-items/3141
+          remote:  !     
+          remote:  !     As such, we recommend that you switch to using .python-version
+          remote:  !     instead of fixing your runtime.txt file.
+          remote:  !     
+          remote:  !     Delete your runtime.txt file and create a new file in the
+          remote:  !     root directory of your app named:
+          remote:  !     .python-version
+          remote:  !     
+          remote:  !     Make sure to include the '.' character at the start of the
+          remote:  !     filename. Don't add a file extension such as '.txt'.
+          remote:  !     
+          remote:  !     In the new file, specify your app's major Python version number
+          remote:  !     only. Don't include quotes or a 'python-' prefix.
+          remote:  !     
+          remote:  !     For example, to request the latest version of Python #{DEFAULT_PYTHON_MAJOR_VERSION},
+          remote:  !     update your .python-version file so it contains exactly:
+          remote:  !     #{DEFAULT_PYTHON_MAJOR_VERSION}
+          remote:  !     
+          remote:  !     We strongly recommend that you don't specify the Python patch
+          remote:  !     version number, since it will pin your app to an exact Python
+          remote:  !     version and so stop your app from receiving security updates
+          remote:  !     each time it builds.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        OUTPUT
+      end
+    end
   end
 
-  context 'when runtime.txt contains an invalid python version string' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/python_version_invalid', allow_failure: true) }
+  context 'when runtime.txt contains an EOL Python 2.x version' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/runtime_txt_eol_version', allow_failure: true) }
 
-    include_examples 'aborts the build with a runtime not available message', 'python-3.12.0invalid'
+    it 'aborts the build with an EOL message' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Python app detected
+          remote: -----> Using Python 2.7.18 specified in runtime.txt
+          remote: 
+          remote:  !     Error: The requested Python version has reached end-of-life.
+          remote:  !     
+          remote:  !     Python 2.7 has reached its upstream end-of-life, and is
+          remote:  !     therefore no longer receiving security updates:
+          remote:  !     https://devguide.python.org/versions/#supported-versions
+          remote:  !     
+          remote:  !     As such, it's no longer supported by this buildpack:
+          remote:  !     https://devcenter.heroku.com/articles/python-support#supported-python-versions
+          remote:  !     
+          remote:  !     Please upgrade to at least Python 3.10 by changing the
+          remote:  !     version in your runtime.txt file.
+          remote:  !     
+          remote:  !     If possible, we recommend upgrading all the way to Python #{DEFAULT_PYTHON_MAJOR_VERSION},
+          remote:  !     since it contains many performance and usability improvements.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        OUTPUT
+      end
+    end
   end
 
-  context 'when runtime.txt contains stray whitespace' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/runtime_txt_with_stray_whitespace') }
+  # This also tests runtime.txt support for the major version only syntax, as well as the handling
+  # of runtime.txt files that contain stray whitespace.
+  context 'when there is both a runtime.txt and .python-version file' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/runtime_txt_and_python_version_file') }
 
-    include_examples 'builds with the requested Python version', LATEST_PYTHON_3_12
+    it 'builds with the version from runtime.txt' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Python app detected
+          remote: -----> Using Python 3.13 specified in runtime.txt
+          remote: 
+          remote:  !     Warning: The runtime.txt file is deprecated.
+          remote:  !     
+          remote:  !     The runtime.txt file is deprecated since it has been replaced
+          remote:  !     by the more widely supported .python-version file:
+          remote:  !     https://devcenter.heroku.com/changelog-items/3141
+          remote:  !     
+          remote:  !     Please switch to using a .python-version file instead.
+          remote:  !     
+          remote:  !     Delete your runtime.txt file and create a new file in the
+          remote:  !     root directory of your app named:
+          remote:  !     .python-version
+          remote:  !     
+          remote:  !     Make sure to include the '.' character at the start of the
+          remote:  !     filename. Don't add a file extension such as '.txt'.
+          remote:  !     
+          remote:  !     In the new file, specify your app's major Python version number
+          remote:  !     only. Don't include quotes or a 'python-' prefix.
+          remote:  !     
+          remote:  !     For example, to request the latest version of Python 3.13,
+          remote:  !     update your .python-version file so it contains exactly:
+          remote:  !     3.13
+          remote:  !     
+          remote:  !     We strongly recommend that you don't specify the Python patch
+          remote:  !     version number, since it will pin your app to an exact Python
+          remote:  !     version and so stop your app from receiving security updates
+          remote:  !     each time it builds.
+          remote:  !     
+          remote:  !     In the future support for runtime.txt will be removed and
+          remote:  !     this warning will be made an error.
+          remote: 
+          remote: -----> Installing Python #{LATEST_PYTHON_3_13}
+          remote: -----> Installing pip #{PIP_VERSION}
+          remote: -----> Installing dependencies using 'pip install -r requirements.txt'
+        OUTPUT
+      end
+    end
   end
 
   context 'when the requested Python version has changed since the last build' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/python_3.11') }
+    let(:app) { Hatchet::Runner.new('spec/fixtures/python_3.10') }
 
     it 'builds with the new Python version after removing the old install' do
       app.deploy do |app|
-        File.write('runtime.txt', "python-#{LATEST_PYTHON_3_12}")
+        File.write('.python-version', '3.13')
         app.commit!
         app.push!
-        # TODO: The output shouldn't say "installing from cache", since it's not.
         expect(clean_output(app.output)).to include(<<~OUTPUT)
           remote: -----> Python app detected
-          remote: -----> Using Python version specified in runtime.txt
-          remote: -----> Python version has changed from python-#{LATEST_PYTHON_3_11} to python-#{LATEST_PYTHON_3_12}, clearing cache
-          remote: -----> No change in requirements detected, installing from cache
-          remote: -----> Installing python-#{LATEST_PYTHON_3_12}
-          remote: -----> Installing pip #{PIP_VERSION}, setuptools #{SETUPTOOLS_VERSION} and wheel #{WHEEL_VERSION}
-          remote: -----> Installing SQLite3
-          remote: -----> Installing requirements with pip
-          remote:        Collecting urllib3 (from -r requirements.txt (line 1))
+          remote: -----> Using Python 3.13 specified in .python-version
+          remote: -----> Discarding cache since:
+          remote:        - The Python version has changed from #{LATEST_PYTHON_3_10} to #{LATEST_PYTHON_3_13}
+          remote: -----> Installing Python #{LATEST_PYTHON_3_13}
+          remote: -----> Installing pip #{PIP_VERSION}
+          remote: -----> Installing dependencies using 'pip install -r requirements.txt'
+          remote:        Collecting typing-extensions==4.15.0 (from -r requirements.txt (line 2))
         OUTPUT
       end
     end
diff --git a/spec/hatchet/stack_spec.rb b/spec/hatchet/stack_spec.rb
index 35f05dfbf..0aebe7179 100644
--- a/spec/hatchet/stack_spec.rb
+++ b/spec/hatchet/stack_spec.rb
@@ -3,63 +3,98 @@
 require_relative '../spec_helper'
 
 RSpec.describe 'Stack changes' do
-  context 'when the stack is upgraded from Heroku-22 to Heroku-24', stacks: %w[heroku-22] do
-    # This test performs an initial build using an older buildpack version, followed
-    # by a build using the current version. This ensures that the current buildpack
-    # can successfully read the stack metadata written to the build cache in the past.
-    # The buildpack version chosen is one which had an older default Python version, so
-    # we can also prove that clearing the cache didn't lose the Python version metadata.
-    let(:buildpacks) { ['https://github.com/heroku/heroku-buildpack-python#v250'] }
+  context 'when the stack is upgraded from Heroku-24 to Heroku-26', stacks: %w[heroku-24] do
+    # This test performs an initial build using an older buildpack version, followed by a build
+    # using the current version. This ensures that the current buildpack can successfully read
+    # the stack metadata written to the build cache in the past. The buildpack version chosen is
+    # the oldest to support Heroku-24, and which had an older default Python version so we can
+    # also prove that clearing the cache didn't lose the sticky Python version metadata.
+    let(:buildpacks) { ['https://github.com/heroku/heroku-buildpack-python#archive/v250'] }
     let(:app) { Hatchet::Runner.new('spec/fixtures/python_version_unspecified', buildpacks:) }
 
     it 'clears the cache before installing again whilst preserving the sticky Python version' do
       app.deploy do |app|
-        expect(app.output).to include('Building on the Heroku-22 stack')
-        app.update_stack('heroku-24')
+        expect(app.output).to include('Building on the Heroku-24 stack')
+        app.update_stack('heroku-26')
         update_buildpacks(app, [:default])
         app.commit!
         app.push!
-        # TODO: The requirements output shouldn't say "installing from cache", since it's not.
         expect(clean_output(app.output)).to include(<<~OUTPUT)
           remote: -----> Python app detected
-          remote: -----> No Python version was specified. Using the same version as the last build: python-3.12.3
-          remote:        To use a different version, see: https://devcenter.heroku.com/articles/python-runtimes
+          remote: -----> No Python version was specified. Using the same major version as the last build: Python 3.12
+          remote: 
+          remote:  !     Warning: No Python version was specified.
+          remote:  !     
+          remote:  !     Your app doesn't specify a Python version and so the buildpack
+          remote:  !     picked a default version for you.
+          remote:  !     
+          remote:  !     Relying on this default version isn't recommended, since it
+          remote:  !     can change over time and may not be consistent with your local
+          remote:  !     development environment, CI or other instances of your app.
+          remote:  !     
+          remote:  !     Please configure an explicit Python version for your app.
+          remote:  !     
+          remote:  !     Create a new file in the root directory of your app named:
+          remote:  !     .python-version
+          remote:  !     
+          remote:  !     Make sure to include the '.' character at the start of the
+          remote:  !     filename. Don't add a file extension such as '.txt'.
           remote:  !     
-          remote:  !     A Python security update is available! Upgrade as soon as possible to: python-#{LATEST_PYTHON_3_12}
-          remote:  !     See: https://devcenter.heroku.com/articles/python-runtimes
+          remote:  !     In the new file, specify your app's major Python version number
+          remote:  !     only. Don't include quotes or a 'python-' prefix.
           remote:  !     
-          remote: -----> Stack has changed from heroku-22 to heroku-24, clearing cache
-          remote: -----> No change in requirements detected, installing from cache
-          remote: -----> Installing python-3.12.3
-          remote: -----> Installing pip #{PIP_VERSION}, setuptools #{SETUPTOOLS_VERSION} and wheel #{WHEEL_VERSION}
-          remote: -----> Installing SQLite3
-          remote: -----> Installing requirements with pip
-          remote:        Collecting urllib3 (from -r requirements.txt (line 1))
+          remote:  !     For example, to request the latest version of Python 3.12,
+          remote:  !     update your .python-version file so it contains exactly:
+          remote:  !     3.12
+          remote:  !     
+          remote:  !     We strongly recommend that you don't specify the Python patch
+          remote:  !     version number, since it will pin your app to an exact Python
+          remote:  !     version and so stop your app from receiving security updates
+          remote:  !     each time it builds.
+          remote:  !     
+          remote:  !     If your app already has a .python-version file, check that it:
+          remote:  !     
+          remote:  !     1. Is in the top level directory (not a subdirectory).
+          remote:  !     2. Is named exactly '.python-version' in all lowercase.
+          remote:  !     3. Isn't listed in '.gitignore' or '.slugignore'.
+          remote:  !     4. Has been added to the Git repository using 'git add --all'
+          remote:  !        and then committed using 'git commit'.
+          remote:  !     
+          remote:  !     In the future we will require the use of a .python-version
+          remote:  !     file and this warning will be made an error.
+          remote: 
+          remote: -----> Discarding cache since:
+          remote:        - The stack has changed from heroku-24 to heroku-26
+          remote:        - The Python version has changed from 3.12.3 to #{LATEST_PYTHON_3_12}
+          remote:        - The buildpack cache format has changed
+          remote:        - The legacy SQLite3 headers and CLI binary need to be uninstalled
+          remote: -----> Installing Python #{LATEST_PYTHON_3_12}
+          remote: -----> Installing pip #{PIP_VERSION} and setuptools #{SETUPTOOLS_VERSION}
+          remote: -----> Installing dependencies using 'pip install -r requirements.txt'
+          remote:        Collecting typing-extensions==4.15.0 (from -r requirements.txt (line 2))
         OUTPUT
       end
     end
   end
 
-  context 'when the stack is downgraded from Heroku-24 to Heroku-22', stacks: %w[heroku-24] do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/python_version_unspecified') }
+  context 'when the stack is downgraded from Heroku-26 to Heroku-24', stacks: %w[heroku-26] do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/python_3.14') }
 
     it 'clears the cache before installing again' do
       app.deploy do |app|
-        expect(app.output).to include('Building on the Heroku-24 stack')
-        app.update_stack('heroku-22')
+        expect(app.output).to include('Building on the Heroku-26 stack')
+        app.update_stack('heroku-24')
         app.commit!
         app.push!
         expect(clean_output(app.output)).to include(<<~OUTPUT)
           remote: -----> Python app detected
-          remote: -----> No Python version was specified. Using the same version as the last build: python-#{DEFAULT_PYTHON_VERSION}
-          remote:        To use a different version, see: https://devcenter.heroku.com/articles/python-runtimes
-          remote: -----> Stack has changed from heroku-24 to heroku-22, clearing cache
-          remote: -----> No change in requirements detected, installing from cache
-          remote: -----> Installing python-#{DEFAULT_PYTHON_VERSION}
-          remote: -----> Installing pip #{PIP_VERSION}, setuptools #{SETUPTOOLS_VERSION} and wheel #{WHEEL_VERSION}
-          remote: -----> Installing SQLite3
-          remote: -----> Installing requirements with pip
-          remote:        Collecting urllib3 (from -r requirements.txt (line 1))
+          remote: -----> Using Python 3.14 specified in .python-version
+          remote: -----> Discarding cache since:
+          remote:        - The stack has changed from heroku-26 to heroku-24
+          remote: -----> Installing Python #{LATEST_PYTHON_3_14}
+          remote: -----> Installing pip #{PIP_VERSION}
+          remote: -----> Installing dependencies using 'pip install -r requirements.txt'
+          remote:        Collecting typing-extensions==4.15.0 (from -r requirements.txt (line 2))
         OUTPUT
       end
     end
diff --git a/spec/hatchet/uv_spec.rb b/spec/hatchet/uv_spec.rb
new file mode 100644
index 000000000..a3b3e2f6f
--- /dev/null
+++ b/spec/hatchet/uv_spec.rb
@@ -0,0 +1,479 @@
+# frozen_string_literal: true
+
+require_relative '../spec_helper'
+
+RSpec.describe 'uv support' do
+  context 'with a uv.lock' do
+    let(:buildpacks) { [:default, 'heroku-community/inline'] }
+    let(:app) { Hatchet::Runner.new('spec/fixtures/uv_basic', buildpacks:) }
+
+    it 'installs successfully using uv and on rebuilds uses the cache' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
+          remote: -----> Python app detected
+          remote: -----> Using Python #{DEFAULT_PYTHON_MAJOR_VERSION} specified in .python-version
+          remote: -----> Installing Python #{DEFAULT_PYTHON_FULL_VERSION}
+          remote: -----> Installing uv #{UV_VERSION}
+          remote: -----> Installing dependencies using 'uv sync --locked --no-default-groups'
+          remote:        Resolved .+ packages in .+s
+          remote:        Prepared 1 package in .+s
+          remote:        Installed 1 package in .+s
+          remote:        Bytecode compiled 1 file in .+s
+          remote:         \\+ typing-extensions==4.15.0
+          remote: -----> Running bin/post_compile hook
+          remote:        BUILD_DIR=/tmp/build_.+
+          remote:        CACHE_DIR=/tmp/codon/tmp/cache
+          remote:        C_INCLUDE_PATH=/app/.heroku/python/include
+          remote:        CPLUS_INCLUDE_PATH=/app/.heroku/python/include
+          remote:        ENV_DIR=/tmp/.+
+          remote:        LANG=en_US.UTF-8
+          remote:        LD_LIBRARY_PATH=/app/.heroku/python/lib
+          remote:        LIBRARY_PATH=/app/.heroku/python/lib
+          remote:        PATH=/tmp/codon/tmp/cache/.heroku/python-uv:/app/.heroku/python/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+          remote:        PKG_CONFIG_PATH=/app/.heroku/python/lib/pkg-config
+          remote:        PYTHONUNBUFFERED=1
+          remote:        UV_CACHE_DIR=/tmp/uv-cache
+          remote:        UV_LINK_MODE=hardlink
+          remote:        UV_NO_MANAGED_PYTHON=1
+          remote:        UV_PROJECT_ENVIRONMENT=/app/.heroku/python
+          remote:        UV_PYTHON_DOWNLOADS=never
+          remote: -----> Saving cache
+          remote: -----> Inline app detected
+          remote: LANG=en_US.UTF-8
+          remote: LD_LIBRARY_PATH=/app/.heroku/python/lib
+          remote: LIBRARY_PATH=/app/.heroku/python/lib
+          remote: PATH=/app/.heroku/python/bin:/tmp/codon/tmp/cache/.heroku/python-uv:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+          remote: PYTHONHOME=/app/.heroku/python
+          remote: PYTHONPATH=/app
+          remote: PYTHONUNBUFFERED=true
+          remote: UV_CACHE_DIR=/tmp/uv-cache
+          remote: UV_LINK_MODE=hardlink
+          remote: UV_NO_MANAGED_PYTHON=1
+          remote: UV_PROJECT_ENVIRONMENT=/app/.heroku/python
+          remote: UV_PYTHON_DOWNLOADS=never
+          remote: 
+          remote: \\['',
+          remote:  '/app',
+          remote:  '/app/.heroku/python/lib/python314.zip',
+          remote:  '/app/.heroku/python/lib/python3.14',
+          remote:  '/app/.heroku/python/lib/python3.14/lib-dynload',
+          remote:  '/app/.heroku/python/lib/python3.14/site-packages'\\]
+          remote: 
+          remote: uv #{UV_VERSION} \\(x86_64-unknown-linux-gnu\\)
+          remote: Using Python #{DEFAULT_PYTHON_FULL_VERSION} environment at: /app/.heroku/python
+          remote: Package           Version
+          remote: ----------------- -------
+          remote: typing-extensions 4.15.0
+          remote: 
+          remote: <module 'typing_extensions' from '/app/.heroku/python/lib/python3.14/site-packages/typing_extensions.py'>
+          remote: 
+          remote: \\{
+          remote:   "cache_restore_duration": [0-9.]+,
+          remote:   "cache_save_duration": [0-9.]+,
+          remote:   "cache_status": "empty",
+          remote:   "dependencies_install_duration": [0-9.]+,
+          remote:   "django_collectstatic_duration": [0-9.]+,
+          remote:   "nltk_downloader_duration": [0-9.]+,
+          remote:   "package_manager": "uv",
+          remote:   "package_manager_install_duration": [0-9.]+,
+          remote:   "post_compile_hook": true,
+          remote:   "post_compile_hook_duration": [0-9.]+,
+          remote:   "pre_compile_hook": false,
+          remote:   "python_install_duration": [0-9.]+,
+          remote:   "python_version": "#{DEFAULT_PYTHON_FULL_VERSION}",
+          remote:   "python_version_major": "3.14",
+          remote:   "python_version_origin": ".python-version",
+          remote:   "python_version_outdated": false,
+          remote:   "python_version_pinned": false,
+          remote:   "python_version_requested": "3.14",
+          remote:   "total_duration": [0-9.]+,
+          remote:   "uv_version": "#{UV_VERSION}"
+          remote: \\}
+        REGEX
+
+        app.commit!
+        app.push!
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
+          remote: -----> Python app detected
+          remote: -----> Using Python #{DEFAULT_PYTHON_MAJOR_VERSION} specified in .python-version
+          remote: -----> Restoring cache
+          remote: -----> Using cached install of Python #{DEFAULT_PYTHON_FULL_VERSION}
+          remote: -----> Using cached uv #{UV_VERSION}
+          remote: -----> Installing dependencies using 'uv sync --locked --no-default-groups'
+          remote:        Resolved .+ packages in .+s
+          remote:        Bytecode compiled 1 file in .+s
+          remote: -----> Running bin/post_compile hook
+          remote:        .+
+          remote: -----> Saving cache
+          remote: -----> Inline app detected
+        REGEX
+
+        command = 'bin/print-env-vars.sh && if command -v uv; then echo "uv unexpectedly found!" && exit 1; fi'
+        expect(normalize_trailing_newlines(app.run(command))).to eq(<<~OUTPUT)
+          DYNO_RAM=512
+          FORWARDED_ALLOW_IPS=*
+          GUNICORN_CMD_ARGS=--access-logfile -
+          LANG=en_US.UTF-8
+          LD_LIBRARY_PATH=/app/.heroku/python/lib
+          LIBRARY_PATH=/app/.heroku/python/lib
+          PATH=/app/.heroku/python/bin:/usr/local/bin:/usr/bin:/bin
+          PYTHONHOME=/app/.heroku/python
+          PYTHONPATH=/app
+          PYTHONUNBUFFERED=true
+          WEB_CONCURRENCY=2
+          WEB_CONCURRENCY_SET_BY=heroku/python
+        OUTPUT
+        expect($CHILD_STATUS.exitstatus).to eq(0)
+      end
+    end
+  end
+
+  # TODO: Enable on Heroku-26 after the uv and default Python versions next change,
+  # since for now there isn't a historic buildpack version we can use in this test
+  # whose stack check permits Heroku-26 and that also uses older uv/Python versions.
+  context 'when the uv and Python versions have changed since the last build', stacks: %w[heroku-22 heroku-24] do
+    let(:buildpacks) { ['https://github.com/heroku/heroku-buildpack-python#v313'] }
+    let(:app) { Hatchet::Runner.new('spec/fixtures/uv_basic', buildpacks:) }
+
+    it 'clears the cache before installing' do
+      app.deploy do |app|
+        update_buildpacks(app, [:default])
+        FileUtils.rm('bin/post_compile')
+        app.commit!
+        app.push!
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
+          remote: -----> Python app detected
+          remote: -----> Using Python 3.14 specified in .python-version
+          remote: -----> Discarding cache since:
+          remote:        - The Python version has changed from 3.14.0 to #{LATEST_PYTHON_3_14}
+          remote:        - The uv version has changed from 0.8.23 to #{UV_VERSION}
+          remote: -----> Installing Python #{LATEST_PYTHON_3_14}
+          remote: -----> Installing uv #{UV_VERSION}
+          remote: -----> Installing dependencies using 'uv sync --locked --no-default-groups'
+          remote:        Resolved .+ packages in .+s
+          remote:        Prepared 1 package in .+s
+          remote:        Installed 1 package in .+s
+          remote:        Bytecode compiled 1 file in .+s
+          remote:         \\+ typing-extensions==4.15.0
+          remote: -----> Saving cache
+          remote: -----> Discovering process types
+        REGEX
+      end
+    end
+  end
+
+  # uv doesn't support editable mode with VCS dependencies, so unlike the editable tests for the other
+  # package managers the gunicorn dependency isn't editable. However, we still include it to ensure we
+  # have VCS coverage. See: https://github.com/astral-sh/uv/issues/5442
+  context 'when uv.lock contains editable requirements and a VCS dependency' do
+    let(:buildpacks) { [:default, 'heroku-community/inline'] }
+    let(:app) { Hatchet::Runner.new('spec/fixtures/uv_editable', buildpacks:) }
+
+    it 'rewrites .pth and finder paths correctly for hooks, later buildpacks, runtime and cached builds' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
+          remote: -----> Installing dependencies using 'uv sync --locked --no-default-groups'
+          remote:        Resolved 5 packages in .+s
+          remote:           .+
+          remote:        Prepared 5 packages in .+s
+          remote:        Installed 5 packages in .+s
+          remote:        Bytecode compiled .+ files in .+s
+          remote:         \\+ gunicorn==23.0.0 \\(from git\\+https://github.com/benoitc/gunicorn@56b5ad87f8d72a674145c273ed8f547513c2b409\\)
+          remote:         \\+ local-package-pyproject-toml==0.0.1 \\(from file:///tmp/build_.+/packages/local_package_pyproject_toml\\)
+          remote:         \\+ local-package-setup-py==0.0.1 \\(from file:///tmp/build_.+/packages/local_package_setup_py\\)
+          remote:         \\+ packaging==25.0
+          remote:         \\+ uv-editable==0.0.0 \\(from file:///tmp/build_.+\\)
+          remote: -----> Running bin/post_compile hook
+          remote:        __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.+/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
+          remote:        __editable___local_package_setup_py_0_0_1_finder.py:/tmp/build_.+/packages/local_package_setup_py/local_package_setup_py'}
+          remote:        uv_editable.pth:/tmp/build_.+/src
+          remote:        
+          remote:        Running entrypoint for the current package: Hello from uv-editable!
+          remote:        Running entrypoint for the pyproject.toml-based local package: Hello from pyproject.toml!
+          remote:        Running entrypoint for the setup.py-based local package: Hello from setup.py!
+          remote:        Running entrypoint for the VCS package: gunicorn \\(version 23.0.0\\)
+          remote: -----> Saving cache
+          remote: -----> Inline app detected
+          remote: __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.+/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
+          remote: __editable___local_package_setup_py_0_0_1_finder.py:/tmp/build_.+/packages/local_package_setup_py/local_package_setup_py'}
+          remote: uv_editable.pth:/tmp/build_.+/src
+          remote: 
+          remote: Running entrypoint for the current package: Hello from uv-editable!
+          remote: Running entrypoint for the pyproject.toml-based local package: Hello from pyproject.toml!
+          remote: Running entrypoint for the setup.py-based local package: Hello from setup.py!
+          remote: Running entrypoint for the VCS package: gunicorn \\(version 23.0.0\\)
+        REGEX
+
+        # Test rewritten paths work at runtime.
+        expect(app.run('bin/test-entrypoints.sh')).to include(<<~OUTPUT)
+          __editable___local_package_pyproject_toml_0_0_1_finder.py:/app/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
+          __editable___local_package_setup_py_0_0_1_finder.py:/app/packages/local_package_setup_py/local_package_setup_py'}
+          uv_editable.pth:/app/src
+
+          Running entrypoint for the current package: Hello from uv-editable!
+          Running entrypoint for the pyproject.toml-based local package: Hello from pyproject.toml!
+          Running entrypoint for the setup.py-based local package: Hello from setup.py!
+          Running entrypoint for the VCS package: gunicorn (version 23.0.0)
+        OUTPUT
+
+        # Test that the cached .pth files work correctly.
+        app.commit!
+        app.push!
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX, Regexp::MULTILINE))
+          remote: -----> Installing dependencies using 'uv sync --locked --no-default-groups'
+          remote:        Resolved 5 packages in .+
+          remote:           .+
+          remote:        Prepared 3 packages in .+s
+          remote:        Uninstalled 3 packages in .+s
+          remote:        Installed 3 packages in .+s
+          remote:        Bytecode compiled .+ files in .+s
+          remote:         - local-package-pyproject-toml==0.0.1 \\(from file:///tmp/build_.+/packages/local_package_pyproject_toml\\)
+          remote:         \\+ local-package-pyproject-toml==0.0.1 \\(from file:///tmp/build_.+/packages/local_package_pyproject_toml\\)
+          remote:         - local-package-setup-py==0.0.1 \\(from file:///tmp/build_.+/packages/local_package_setup_py\\)
+          remote:         \\+ local-package-setup-py==0.0.1 \\(from file:///tmp/build_.+/packages/local_package_setup_py\\)
+          remote:         - uv-editable==0.0.0 \\(from file:///tmp/build_.+\\)
+          remote:         \\+ uv-editable==0.0.0 \\(from file:///tmp/build_.+\\)
+          remote: -----> Running bin/post_compile hook
+          remote:        __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.+/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
+          remote:        __editable___local_package_setup_py_0_0_1_finder.py:/tmp/build_.+/packages/local_package_setup_py/local_package_setup_py'}
+          remote:        uv_editable.pth:/tmp/build_.+/src
+          remote:        
+          remote:        Running entrypoint for the current package: Hello from uv-editable!
+          remote:        Running entrypoint for the pyproject.toml-based local package: Hello from pyproject.toml!
+          remote:        Running entrypoint for the setup.py-based local package: Hello from setup.py!
+          remote:        Running entrypoint for the VCS package: gunicorn \\(version 23.0.0\\)
+          remote: -----> Saving cache
+          remote: -----> Inline app detected
+          remote: __editable___local_package_pyproject_toml_0_0_1_finder.py:/tmp/build_.+/packages/local_package_pyproject_toml/local_package_pyproject_toml'}
+          remote: __editable___local_package_setup_py_0_0_1_finder.py:/tmp/build_.+/packages/local_package_setup_py/local_package_setup_py'}
+          remote: uv_editable.pth:/tmp/build_.+/src
+          remote: 
+          remote: Running entrypoint for the current package: Hello from uv-editable!
+          remote: Running entrypoint for the pyproject.toml-based local package: Hello from pyproject.toml!
+          remote: Running entrypoint for the setup.py-based local package: Hello from setup.py!
+          remote: Running entrypoint for the VCS package: gunicorn \\(version 23.0.0\\)
+        REGEX
+      end
+    end
+  end
+
+  context 'when using our oldest supported Python version' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/uv_oldest_python') }
+
+    it 'installs successfully' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
+          remote: -----> Python app detected
+          remote: -----> Using Python 3.10.0 specified in .python-version
+          remote: 
+          remote:  !     Warning: Support for Python 3.10 is deprecated!
+          remote:  !     
+          remote:  !     Python 3.10 will reach its upstream end-of-life in October 2026,
+          remote:  !     at which point it will no longer receive security updates:
+          remote:  !     https://devguide.python.org/versions/#supported-versions
+          remote:  !     
+          remote:  !     As such, support for Python 3.10 will be removed from this
+          remote:  !     buildpack on 6th January 2027.
+          remote:  !     
+          remote:  !     Upgrade to a newer Python version as soon as possible, by
+          remote:  !     changing the version in your .python-version file.
+          remote:  !     
+          remote:  !     For more information, see:
+          remote:  !     https://devcenter.heroku.com/articles/python-support#supported-python-versions
+          remote: 
+          remote: 
+          remote:  !     Warning: A Python patch update is available!
+          remote:  !     
+          remote:  !     Your app is using Python 3.10.0, however, there is a newer
+          remote:  !     patch release of Python 3.10 available: #{LATEST_PYTHON_3_10}
+          remote:  !     
+          remote:  !     It is important to always use the latest patch version of
+          remote:  !     Python to keep your app secure.
+          remote:  !     
+          remote:  !     Update your .python-version file to use the new version.
+          remote:  !     
+          remote:  !     We strongly recommend that you don't pin your app to an
+          remote:  !     exact Python version such as 3.10.0, and instead only specify
+          remote:  !     the major Python version of 3.10 in your .python-version file.
+          remote:  !     This will allow your app to receive the latest available Python
+          remote:  !     patch version automatically and prevent this warning.
+          remote: 
+          remote: -----> Installing Python 3.10.0
+          remote: -----> Installing uv #{UV_VERSION}
+          remote: -----> Installing dependencies using 'uv sync --locked --no-default-groups'
+          remote:        Resolved 2 packages in .+s
+          remote:        Prepared 1 package in .+s
+          remote:        Installed 1 package in .+s
+          remote:        Bytecode compiled 1 file in .+s
+          remote:         \\+ typing-extensions==4.15.0
+          remote: -----> Saving cache
+        REGEX
+      end
+    end
+  end
+
+  # This tests the error message when there is no .python-version file, and in particular the case where
+  # the buildpack's default Python version is not compatible with `requires-python` in pyproject.toml.
+  # (Since we must prevent uv from downloading its own Python or using system Python, and also
+  # want a clearer error message than using `--python` or `UV_PYTHON` would give us).
+  context 'when there is no .python-version file' do
+    context 'when there is no cached Python version' do
+      let(:app) { Hatchet::Runner.new('spec/fixtures/uv_no_python_version_file', allow_failure: true) }
+
+      it 'fails the build with .python-version instructions' do
+        app.deploy do |app|
+          expect(clean_output(app.output)).to include(<<~OUTPUT)
+            remote: -----> No Python version was specified. Using the buildpack default: Python #{DEFAULT_PYTHON_MAJOR_VERSION}
+            remote: 
+            remote:  !     Error: No Python version was specified.
+            remote:  !     
+            remote:  !     When using the package manager uv on Heroku, you must specify
+            remote:  !     your app's Python version with a .python-version file.
+            remote:  !     
+            remote:  !     To add a .python-version file:
+            remote:  !     
+            remote:  !     1. Make sure you are in the root directory of your app
+            remote:  !        and not a subdirectory.
+            remote:  !     2. Run 'uv python pin #{DEFAULT_PYTHON_MAJOR_VERSION}'
+            remote:  !        (adjust to match your app's major Python version).
+            remote:  !     3. Commit the changes to your Git repository using
+            remote:  !        'git add --all' and then 'git commit'.
+            remote:  !     
+            remote:  !     Note: We strongly recommend that you don't specify the Python
+            remote:  !     patch version number in your .python-version file, since it will
+            remote:  !     pin your app to an exact Python version and so stop your app from
+            remote:  !     receiving security updates each time it builds.
+            remote: 
+            remote:  !     Push rejected, failed to compile Python app.
+          OUTPUT
+        end
+      end
+    end
+
+    context 'when there is a cached Python version' do
+      let(:app) { Hatchet::Runner.new('spec/fixtures/python_version_unspecified', allow_failure: true) }
+
+      it 'fails the build with .python-version instructions' do
+        app.deploy do |app|
+          FileUtils.rm('requirements.txt')
+          FileUtils.cp(FIXTURE_DIR.join('uv_no_python_version_file/pyproject.toml'), '.')
+          FileUtils.cp(FIXTURE_DIR.join('uv_no_python_version_file/uv.lock'), '.')
+          app.commit!
+          app.push!
+          expect(clean_output(app.output)).to include(<<~OUTPUT)
+            remote: -----> No Python version was specified. Using the same major version as the last build: Python #{DEFAULT_PYTHON_MAJOR_VERSION}
+            remote: 
+            remote:  !     Error: No Python version was specified.
+            remote:  !     
+            remote:  !     When using the package manager uv on Heroku, you must specify
+            remote:  !     your app's Python version with a .python-version file.
+            remote:  !     
+            remote:  !     To add a .python-version file:
+            remote:  !     
+            remote:  !     1. Make sure you are in the root directory of your app
+            remote:  !        and not a subdirectory.
+            remote:  !     2. Run 'uv python pin #{DEFAULT_PYTHON_MAJOR_VERSION}'
+            remote:  !        (adjust to match your app's major Python version).
+            remote:  !     3. Commit the changes to your Git repository using
+            remote:  !        'git add --all' and then 'git commit'.
+            remote:  !     
+            remote:  !     Note: We strongly recommend that you don't specify the Python
+            remote:  !     patch version number in your .python-version file, since it will
+            remote:  !     pin your app to an exact Python version and so stop your app from
+            remote:  !     receiving security updates each time it builds.
+            remote: 
+            remote:  !     Push rejected, failed to compile Python app.
+          OUTPUT
+        end
+      end
+    end
+  end
+
+  # This tests the error message when a runtime.txt is present, and in particular the case where
+  # the runtime.txt version is not compatible with `requires-python` in pyproject.toml.
+  # (Since we must prevent uv from downloading its own Python or using system Python, and also
+  # want a clearer error message than using `--python` or `UV_PYTHON` would give us).
+  context 'when there is a runtime.txt file' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/uv_runtime_txt', allow_failure: true) }
+
+    it 'fails the build with runtime.txt migration instructions' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Using Python 3.11 specified in runtime.txt
+          remote: 
+          remote:  !     Error: The runtime.txt file isn't supported when using uv.
+          remote:  !     
+          remote:  !     When using the package manager uv on Heroku, you must specify
+          remote:  !     your app's Python version with a .python-version file and not
+          remote:  !     a runtime.txt file.
+          remote:  !     
+          remote:  !     To switch to a .python-version file:
+          remote:  !     
+          remote:  !     1. Make sure you are in the root directory of your app
+          remote:  !        and not a subdirectory.
+          remote:  !     2. Delete your runtime.txt file.
+          remote:  !     3. Run 'uv python pin 3.11'
+          remote:  !        (adjust to match your app's major Python version).
+          remote:  !     4. Commit the changes to your Git repository using
+          remote:  !        'git add --all' and then 'git commit'.
+          remote:  !     
+          remote:  !     Note: We strongly recommend that you don't specify the Python
+          remote:  !     patch version number in your .python-version file, since it will
+          remote:  !     pin your app to an exact Python version and so stop your app from
+          remote:  !     receiving security updates each time it builds.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        OUTPUT
+      end
+    end
+  end
+
+  # This tests the error message when `requires-python` in pyproject.toml isn't compatible with
+  # the version in .python-version. This might seem unnecessary since it's testing something uv
+  # validates itself, however, the quality of the error message here depends on what uv options
+  # we use (for example, using `--python` or `UV_PYTHON` results in a worse error message).
+  context 'when requires-python in pyproject.toml is incompatible with .python-version' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/uv_mismatched_python_version', allow_failure: true) }
+
+    it 'fails the build' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to include(<<~OUTPUT)
+          remote: -----> Installing dependencies using 'uv sync --locked --no-default-groups'
+          remote:        Using CPython #{LATEST_PYTHON_3_13} interpreter at: /app/.heroku/python/bin/python3.13
+          remote:        error: The Python request from `.python-version` resolved to Python #{LATEST_PYTHON_3_13}, which is incompatible with the project's Python requirement: `==3.12.*` (from `project.requires-python`)
+          remote:        Use `uv python pin` to update the `.python-version` file to a compatible version
+          remote: 
+          remote:  !     Error: Unable to install dependencies using uv.
+          remote:  !     
+          remote:  !     See the log output above for more information.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        OUTPUT
+      end
+    end
+  end
+
+  # This tests not only our handling of failing dependency installation, but also that we're running
+  # uv in such a way that it errors if the lockfile is out of sync, rather than simply updating it.
+  context 'when uv.lock is out of sync with pyproject.toml' do
+    let(:app) { Hatchet::Runner.new('spec/fixtures/uv_lockfile_out_of_sync', allow_failure: true) }
+
+    it 'fails the build' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
+          remote: -----> Installing dependencies using 'uv sync --locked --no-default-groups'
+          remote:        Resolved 2 packages in .+s
+          remote:        error: The lockfile at `uv.lock` needs to be updated, but `--locked` was provided.
+          remote:        
+          remote:        hint: To update the lockfile, run `uv lock`.
+          remote: 
+          remote:  !     Error: Unable to install dependencies using uv.
+          remote:  !     
+          remote:  !     See the log output above for more information.
+          remote: 
+          remote:  !     Push rejected, failed to compile Python app.
+        REGEX
+      end
+    end
+  end
+end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 3efda0c20..fa6deb277 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -1,18 +1,22 @@
 # frozen_string_literal: true
 
 ENV['HATCHET_BUILDPACK_BASE'] ||= 'https://github.com/heroku/heroku-buildpack-python.git'
-ENV['HATCHET_DEFAULT_STACK'] ||= 'heroku-24'
+ENV['HATCHET_DEFAULT_STACK'] ||= 'heroku-26'
 
+require 'English' # for $CHILD_STATUS
 require 'rspec/core'
 require 'rspec/retry'
 require 'hatchet'
 
-LATEST_PYTHON_3_8 = '3.8.19'
-LATEST_PYTHON_3_9 = '3.9.19'
-LATEST_PYTHON_3_10 = '3.10.14'
-LATEST_PYTHON_3_11 = '3.11.9'
-LATEST_PYTHON_3_12 = '3.12.4'
-DEFAULT_PYTHON_VERSION = LATEST_PYTHON_3_12
+FIXTURE_DIR = Pathname.new(__FILE__).parent.join('fixtures')
+
+LATEST_PYTHON_3_10 = '3.10.20'
+LATEST_PYTHON_3_11 = '3.11.15'
+LATEST_PYTHON_3_12 = '3.12.13'
+LATEST_PYTHON_3_13 = '3.13.14'
+LATEST_PYTHON_3_14 = '3.14.6'
+DEFAULT_PYTHON_FULL_VERSION = LATEST_PYTHON_3_14
+DEFAULT_PYTHON_MAJOR_VERSION = DEFAULT_PYTHON_FULL_VERSION.gsub(/\.\d+$/, '')
 
 # The requirement versions are effectively buildpack constants, however, we want
 # Dependabot to be able to update them, which requires that they be in requirements
@@ -24,9 +28,12 @@ def get_requirement_version(package_name)
 end
 
 PIP_VERSION = get_requirement_version('pip')
-SETUPTOOLS_VERSION = get_requirement_version('setuptools')
-WHEEL_VERSION = get_requirement_version('wheel')
 PIPENV_VERSION = get_requirement_version('pipenv')
+POETRY_VERSION = get_requirement_version('poetry')
+UV_VERSION = get_requirement_version('uv')
+# This is hardcoded rather than managed by Dependabot since we can't update to newer versions due to:
+# https://github.com/heroku/heroku-buildpack-python/pull/1630#issuecomment-2324236653
+SETUPTOOLS_VERSION = '70.3.0'
 
 # Work around the return value for `default_buildpack` changing after deploy:
 # https://github.com/heroku/hatchet/issues/180
@@ -44,14 +51,23 @@ def get_requirement_version(package_name)
   config.filter_run_when_matching :focus
   # Allows declaring on which stacks a test/group should run by tagging it with `stacks`.
   config.filter_run_excluding stacks: ->(stacks) { !stacks.include?(ENV.fetch('HATCHET_DEFAULT_STACK')) }
-  # Make rspec-retry output a retry message when its had to retry a test.
+  # Make rspec-retry output a retry message when it's had to retry a test.
   config.verbose_retry = true
 end
 
 def clean_output(output)
-  # Remove trailing whitespace characters added by Git:
-  # https://github.com/heroku/hatchet/issues/162
-  output.gsub(/ {8}(?=\R)/, '')
+  output
+    # Remove trailing whitespace characters added by Git:
+    # https://github.com/heroku/hatchet/issues/162
+    .gsub(/ {8}(?=\R)/, '')
+    # Remove ANSI colour codes used in buildpack output (e.g. error messages).
+    .gsub(/\e\[[0-9;]+m/, '')
+end
+
+def normalize_trailing_newlines(output)
+  # The platform log stream that captures `run`/`run_multi` command output occasionally appends
+  # an extra trailing newline, which otherwise intermittently breaks exact output assertions.
+  output.sub(/\n+\z/, "\n")
 end
 
 def update_buildpacks(app, buildpacks)
diff --git a/vendor/WEB_CONCURRENCY.sh b/vendor/WEB_CONCURRENCY.sh
index d6cc1a234..803b7217f 100755
--- a/vendor/WEB_CONCURRENCY.sh
+++ b/vendor/WEB_CONCURRENCY.sh
@@ -25,43 +25,43 @@
 # exit on error, have to use return not exit, and returning non-zero doesn't have an effect.
 
 function detect_memory_limit_in_mb() {
-  local memory_limit_file='/sys/fs/cgroup/memory/memory.limit_in_bytes'
+	local memory_limit_file='/sys/fs/cgroup/memory/memory.limit_in_bytes'
 
-  # This memory limits file only exists on Heroku, or when using cgroups v1 (Docker < 20.10).
-  if [[ -f "${memory_limit_file}" ]]; then
-    local memory_limit_in_mb=$(($(cat "${memory_limit_file}") / 1048576))
+	# This memory limits file only exists on Heroku, or when using cgroups v1 (Docker < 20.10).
+	if [[ -f "${memory_limit_file}" ]]; then
+		local memory_limit_in_mb=$(($(cat "${memory_limit_file}") / 1048576))
 
-    # Ignore values above 1TB RAM, since when using cgroups v1 the limits file reports a
-    # bogus value of thousands of TB RAM when there is no container memory limit set.
-    if ((memory_limit_in_mb <= 1048576)); then
-      echo "${memory_limit_in_mb}"
-      return 0
-    fi
-  fi
+		# Ignore values above 1TB RAM, since when using cgroups v1 the limits file reports a
+		# bogus value of thousands of TB RAM when there is no container memory limit set.
+		if ((memory_limit_in_mb <= 1048576)); then
+			echo "${memory_limit_in_mb}"
+			return 0
+		fi
+	fi
 
-  return 1
+	return 1
 }
 
 function output() {
-  # Only display log output for web dynos, to prevent breaking one-off dyno scripting use-cases,
-  # and to prevent confusion from messages about WEB_CONCURRENCY in the logs of non-web workers.
-  # (We still actually set the env vars for all dyno types for consistency and easier debugging.)
-  if [[ "${DYNO:-}" == web.* ]]; then
-    echo "Python buildpack: $*" >&2
-  fi
+	# Only display log output for web dynos, to prevent breaking one-off dyno scripting use-cases,
+	# and to prevent confusion from messages about WEB_CONCURRENCY in the logs of non-web workers.
+	# (We still actually set the env vars for all dyno types for consistency and easier debugging.)
+	if [[ "${DYNO:-}" == web.* ]]; then
+		echo "Python buildpack: $*" >&2
+	fi
 }
 
 if ! available_memory_in_mb=$(detect_memory_limit_in_mb); then
-  # This should never occur on Heroku, but will be common for non-Heroku environments such as Dokku.
-  output "Couldn't determine available memory. Skipping automatic configuration of WEB_CONCURRENCY."
-  return 0
+	# This should never occur on Heroku, but will be common for non-Heroku environments such as Dokku.
+	output "Couldn't determine available memory. Skipping automatic configuration of WEB_CONCURRENCY."
+	return 0
 fi
 
 if ! cpu_cores=$(nproc); then
-  # This should never occur in practice, since this buildpack only supports being run on our base
-  # images, and nproc is installed in all of them.
-  output "Couldn't determine number of CPU cores. Skipping automatic configuration of WEB_CONCURRENCY."
-  return 0
+	# This should never occur in practice, since this buildpack only supports being run on our base
+	# images, and nproc is installed in all of them.
+	output "Couldn't determine number of CPU cores. Skipping automatic configuration of WEB_CONCURRENCY."
+	return 0
 fi
 
 output "Detected ${available_memory_in_mb} MB available memory and ${cpu_cores} CPU cores."
@@ -71,25 +71,28 @@ output "Detected ${available_memory_in_mb} MB available memory and ${cpu_cores}
 export DYNO_RAM="${available_memory_in_mb}"
 
 if [[ -v WEB_CONCURRENCY ]]; then
-  output "Skipping automatic configuration of WEB_CONCURRENCY since it's already set."
-  return 0
+	output "Skipping automatic configuration of WEB_CONCURRENCY since it's already set."
+	return 0
 fi
 
+# Make it possible to differentiate between user and buildpack set WEB_CONCURRENCY values.
+export WEB_CONCURRENCY_SET_BY="heroku/python"
+
 minimum_memory_per_process_in_mb=256
 
 # Prevents WEB_CONCURRENCY being set to zero if the environment is extremely memory constrained.
 if ((available_memory_in_mb < minimum_memory_per_process_in_mb)); then
-  max_concurrency_for_available_memory=1
+	max_concurrency_for_available_memory=1
 else
-  max_concurrency_for_available_memory=$((available_memory_in_mb / minimum_memory_per_process_in_mb))
+	max_concurrency_for_available_memory=$((available_memory_in_mb / minimum_memory_per_process_in_mb))
 fi
 
 max_concurrency_for_cpu_cores=$((cpu_cores * 2 + 1))
 
 if ((max_concurrency_for_available_memory < max_concurrency_for_cpu_cores)); then
-  export WEB_CONCURRENCY="${max_concurrency_for_available_memory}"
-  output "Defaulting WEB_CONCURRENCY to ${WEB_CONCURRENCY} based on the available memory."
+	export WEB_CONCURRENCY="${max_concurrency_for_available_memory}"
+	output "Defaulting WEB_CONCURRENCY to ${WEB_CONCURRENCY} based on the available memory."
 else
-  export WEB_CONCURRENCY="${max_concurrency_for_cpu_cores}"
-  output "Defaulting WEB_CONCURRENCY to ${WEB_CONCURRENCY} based on the number of CPU cores."
+	export WEB_CONCURRENCY="${max_concurrency_for_cpu_cores}"
+	output "Defaulting WEB_CONCURRENCY to ${WEB_CONCURRENCY} based on the number of CPU cores."
 fi
diff --git a/vendor/buildpack-stdlib_v8.sh b/vendor/buildpack-stdlib_v8.sh
index 69e0e7036..8f82fc152 100755
--- a/vendor/buildpack-stdlib_v8.sh
+++ b/vendor/buildpack-stdlib_v8.sh
@@ -1,114 +1,62 @@
 #!/usr/bin/env bash
+# shellcheck disable=SC2154 # TODO: Env var is referenced but not assigned.
+
+set -euo pipefail
 
 # Based on:
 # https://raw.githubusercontent.com/heroku/buildpack-stdlib/v8/stdlib.sh
 
-# Standard Output
-# ---------------
-
-# Buildpack Steps.
-puts_step() {
-  if [[ "$*" == "-" ]]; then
-    read -r output
-  else
-    output=$*
-  fi
-  echo -e "\\e[1m\\e[36m=== $output\\e[0m"
-  unset output
-}
-
-# Buildpack Error.
-puts_error() {
-  if [[ "$*" == "-" ]]; then
-    read -r output
-  else
-    output=$*
-  fi
-  echo -e "\\e[1m\\e[31m=!= $output\\e[0m"
-}
-
-# Buildpack Warning.
-puts_warn() {
-  if [[ "$*" == "-" ]]; then
-    read -r output
-  else
-    output=$*
-  fi
-  echo -e "\\e[1m\\e[33m=!= $output\\e[0m"
-}
-
-# Is verbose set?
-is_verbose() {
-  if [[ -n $BUILDPACK_VERBOSE ]]; then
-    return 0
-  else
-    return 1
-  fi
-}
-
-# Buildpack Verbose.
-puts_verbose() {
-  if is_verbose; then
-    if [[ "$*" == "-" ]]; then
-      read -r output
-    else
-      output=$*
-    fi
-    echo "$output"
-    unset output
-  fi
-}
-
 # Buildpack Utilities
 # -------------------
 
 # Usage: $ set-env key value
 # NOTICE: Expects PROFILE_PATH & EXPORT_PATH to be set!
 set_env() {
-  # TODO: automatically create profile path directory if it doesn't exist.
-  echo "export $1=$2" >> "$PROFILE_PATH"
-  echo "export $1=$2" >> "$EXPORT_PATH"
+	# TODO: automatically create profile path directory if it doesn't exist.
+	echo "export $1=$2" >>"${PROFILE_PATH}"
+	echo "export $1=$2" >>"${EXPORT_PATH}"
 }
 
 # Usage: $ set-default-env key value
 # NOTICE: Expects PROFILE_PATH & EXPORT_PATH to be set!
 set_default_env() {
-  echo "export $1=\${$1:-$2}" >> "$PROFILE_PATH"
-  echo "export $1=\${$1:-$2}" >> "$EXPORT_PATH"
+	echo "export $1=\${$1:-$2}" >>"${PROFILE_PATH}"
+	echo "export $1=\${$1:-$2}" >>"${EXPORT_PATH}"
 }
 
 # Usage: $ un-set-env key
 # NOTICE: Expects PROFILE_PATH to be set!
 un_set_env() {
-  echo "unset $1" >> "$PROFILE_PATH"
+	echo "unset $1" >>"${PROFILE_PATH}"
 }
 
 # Usage: $ _env-blacklist pattern
 # Outputs a regex of default blacklist env vars.
 _env_blacklist() {
-  local regex=${1:-''}
-  if [[ -n "$regex" ]]; then
-    regex="|$regex"
-  fi
-  echo "^(PATH|CPATH|CPPATH|LD_PRELOAD|LIBRARY_PATH|LD_LIBRARY_PATH|PYTHONHOME$regex)$"
+	local regex="${1:-}"
+	if [[ -n "${regex}" ]]; then
+		regex="|${regex}"
+	fi
+	echo "^(PATH|CPATH|CPPATH|LD_PRELOAD|LIBRARY_PATH|LD_LIBRARY_PATH|PYTHONHOME${regex})$"
 }
 
 # Usage: $ export-env ENV_DIR WHITELIST BLACKLIST
 # Exports the environment variables defined in the given directory.
 export_env() {
-  local env_dir=${1:-$ENV_DIR}
-  local whitelist=${2:-''}
-  local blacklist
-  blacklist="$(_env_blacklist "$3")"
-  if [[ -d "$env_dir" ]]; then
-    # Environment variable names won't contain characters affected by:
-    # shellcheck disable=SC2045
-    for e in $(ls "$env_dir"); do
-      echo "$e" | grep -E "$whitelist" | grep -qvE "$blacklist" &&
-      export "$e=$(cat "$env_dir/$e")"
-      :
-    done
-  fi
+	local env_dir="${1:-${ENV_DIR}}"
+	local whitelist="${2:-}"
+	local blacklist
+	blacklist="$(_env_blacklist "${3:-}")"
+	if [[ -d "${env_dir}" ]]; then
+		local e
+		# Environment variable names won't contain characters affected by:
+		# shellcheck disable=SC2045
+		for e in $(ls "${env_dir}"); do
+			echo "${e}" | grep -E "${whitelist}" | grep -qvE "${blacklist}" \
+				&& export "${e}=$(cat "${env_dir}/${e}")"
+			:
+		done
+	fi
 }
 
 # Usage: $ sub-env command
@@ -118,16 +66,10 @@ export_env() {
 #    WHITELIST=${2:-''}
 #    BLACKLIST=${3:-'^(GIT_DIR|PYTHONHOME|LD_LIBRARY_PATH|LIBRARY_PATH|PATH)$'}
 sub_env() {
-  (
-    # TODO: Fix https://github.com/heroku/buildpack-stdlib/issues/37
-    # shellcheck disable=SC2153
-    export_env "$ENV_DIR" "$WHITELIST" "$BLACKLIST"
-
-    "$@"
-  )
-}
+	(
+		# TODO: Fix https://github.com/heroku/buildpack-stdlib/issues/37
+		export_env "${ENV_DIR}" "${WHITELIST:-}" "${BLACKLIST:-}"
 
-# Returns the current time, in milliseconds.
-nowms() {
-  date +%s%3N
+		"${@}"
+	)
 }