🌱 Fix changelog fragment check for fork PRs

[ibolton336]

Fixes #48.

The changelog job runs under pull_request_target and checked out github.event.pull_request.head.sha, which actions/checkout now refuses for fork PRs ("Refusing to check out fork pull request code from a 'pull_request_target' workflow"). Every fork PR of type feature/bugfix/breaking failed the check — e.g. this run on PR #35.

Since the job only diffs file names and never executes PR code, this checks out the base repo and fetches the PR head as a plain ref (git fetch origin pull/<n>/head:pr-head), then diffs origin/<base>...pr-head. Fork code is never checked out into the workspace, so no allow-unsafe-pr-checkout: true escape hatch is needed and the workflow keeps its safety guarantees.

Verification: YAML validated; the diff expression is unchanged apart from HEAD → pr-head. The fix itself can only be fully exercised by a fork PR against a repo where this workflow already runs on main (pull_request_target uses the base branch's workflow definition), so the real proof will be the next fork PR after this merges.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Chores
  • Improved pull request checks for changelog fragments.
  • Changelog verification now more reliably compares proposed changes with the target branch.
  • Updated validation behavior helps ensure checks run consistently without affecting the application experience.

[coderabbitai]

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 6ba7a8b1-2a9d-450f-a6d2-25d5f9dacc71

📥 Commits

Reviewing files that changed from the base of the PR and between 17c93b5 and 2164d7c.

📒 Files selected for processing (1)

• .github/workflows/pr-checks.yml

📝 Walkthrough

Walkthrough

The changelog workflow now checks out the base repository, fetches the pull request head into pr-head, and compares that ref with the base branch when verifying changelog fragments.

Changes

Changelog verification

Layer / File(s)	Summary
Fetch and diff pull request ref .github/workflows/pr-checks.yml	The changelog job fetches the pull request head as pr-head and uses it in the base-to-head diff without checking out fork code.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely summarizes the main workflow fix for fork PR changelog checks.
Description check	✅ Passed	The description explains the bug, the fix, and verification, and it fits the repository's template requirements.
Linked Issues check	✅ Passed	The workflow changes match issue #48 by avoiding fork checkout, fetching the PR head as a ref, and diffing against it.
Out of Scope Changes check	✅ Passed	The pull request appears scoped to the changelog workflow fix with no unrelated changes introduced.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In @.github/workflows/pr-checks.yml:
- Around line 29-31: Update the actions/checkout@v4 step to set
persist-credentials to false alongside fetch-depth, ensuring the privileged
token is not retained in local Git configuration while preserving the
full-history checkout.
- Around line 34-36: Update the “Check for changelog fragment” step to read the
pull request base ref through a dedicated environment variable rather than
interpolating the GitHub context directly in the shell command. Add the
`:!changes/unreleased/template.yaml` exclusion to the git diff pathspecs so the
fragment list matches the downstream changelog discovery behavior.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 106cb44e-b061-4eb4-a3ad-47e251d7aad8

📥 Commits

Reviewing files that changed from the base of the PR and between 0fbaaba and 17c93b5.

📒 Files selected for processing (1)

• .github/workflows/pr-checks.yml