Run affected-only validation in CI

.github/workflows/validate.yml

@@ -13,6 +13,9 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v4
+        with:
+          # Full history so affected validation can diff against the base commit.
+          fetch-depth: 0
 
       - name: Set up Flutter
         uses: subosito/flutter-action@v2
@@ -22,5 +25,12 @@ jobs:
       - name: Install dependencies
         run: flutter pub get
 
-      - name: Validate workspace
-        run: dart run melos run validate
+      # Validate only the packages affected by the diff. affected_validate.dart
+      # format-checks every changed .dart file and analyzes/tests the affected
+      # packages (incl. dnd_kit_website), and falls back to validate:full when a
+      # workspace, tooling, workflow, or pubspec file changes.
+      - name: Validate affected
+        env:
+          # PR: diff against the base commit. Push to main: against the prior tip.
+          MELOS_DIFF: ${{ github.event_name == 'pull_request' && github.event.pull_request.base.sha || github.event.before }}
+        run: dart run melos run validate:affected

docs/stories/phase-27-ci-affected-validation/US-075-validate-affected-in-ci/story.md

@@ -0,0 +1,81 @@
+# US-075 Run affected-only validation in the Validate CI
+
+## Status
+
+implemented
+
+## Lane
+
+normal
+
+## Product Contract
+
+The Validate workflow validates only the packages affected by a change instead
+of always running `validate:full`. It runs on pull requests and on pushes to
+`main` (so a direct push to `main` is still validated), and the website package
+(`dnd_kit_website`) is covered. Structural changes still escalate to full
+validation.
+
+## Relevant Product Docs
+
+- `.github/workflows/validate.yml`
+- `tool/affected_validate.dart` (US-054 affected tooling)
+- `pubspec.yaml` (`melos` scripts: `validate:affected`, `analyze:affected`)
+
+## Acceptance Criteria
+
+- `validate.yml` runs `dart run melos run validate:affected` (not `validate`),
+  with `fetch-depth: 0` so the tool can diff against a base commit.
+- The diff base is event-aware: the PR base commit on `pull_request`, the prior
+  tip (`github.event.before`) on `push` to `main`.
+- Triggers remain `pull_request` and `push` to `main` — direct pushes to `main`
+  are validated, not only PRs.
+- A change under `website/` is validated: every changed `.dart` file is
+  format-checked and `dnd_kit_website` is analyzed.
+- A change to `tool/`, `scripts/`, `.github/workflows/`, root `pubspec.*`, or
+  `analysis_options.yaml` still falls back to `validate:full`.
+
+## Design Notes
+
+- No change to `affected_validate.dart` was needed: it already format-checks
+  every changed `.dart` file (so `website/lib/*.dart` drift is caught) and
+  analyzes the package that owns each changed file — `dnd_kit_website` is a melos
+  workspace package, so website analyze is selected. Docs-only files
+  (`readme.md`, `changelog.md`, `doc/`, …) are ignored; workspace/tooling/
+  workflow/pubspec changes force `validate:full`.
+- Diff base: `MELOS_DIFF` is set to
+  `github.event.pull_request.base.sha` on PRs and `github.event.before` on
+  pushes; the tool reads `MELOS_DIFF` (default `HEAD`).
+- Edge case: a push whose `before` is all-zero (a brand-new branch or a
+  force-push) has no usable base; normal merges to `main` carry a valid prior
+  tip, so this is acceptable for the `main` push path. (Follow-up if it ever
+  bites: guard the env and fall back to `validate:full`.)
+- Builds on US-054, which introduced and accepted affected-only validation with
+  a full-validation safety fallback; this story only adopts it in CI.
+
+## Validation
+
+When updating durable proof status, use numeric booleans:
+`scripts/bin/harness-cli story update --id US-075 --unit 0 --integration 0 --e2e 0 --platform 1`.
+
+| Layer | Expected proof |
+| --- | --- |
+| Unit | n/a |
+| Integration | n/a |
+| E2E | n/a |
+| Platform | `validate.yml` runs green on a PR and on a push to `main`, selecting only affected packages |
+| Release | First green affected run on `main` |
+
+## Harness Delta
+
+New phase folder `phase-27-ci-affected-validation`. No template or tooling
+change; reuses the US-054 affected validator.
+
+## Evidence
+
+- `dart run tool/affected_validate.dart validate --files=website/lib/site.dart`
+  → changed-file format check passes, `dart analyze` on `dnd_kit_website`
+  SUCCESS, tests skipped (no `test/` dir).
+- `affected_validate.dart plan` for `website/lib/site.dart` and
+  `website/web/styles.tw.css` selects `dnd_kit_website`; `website/README.md` is
+  reported docs-only / ignored.