fix: detect merged release changes

[mktbsh]

What changed

• Compare the pushed commit with its first parent when detecting a merged release PR.

Why

git show --name-only returned no paths for the merge commit produced by release PR #3. The workflow therefore skipped GoReleaser, leaving version 0.2.0 without its tag or GitHub Release and blocking subsequent release-please runs.

Validation

• actionlint .github/workflows/release.yml
• Release PR chore(main): release 0.2.0 #3 merge detects .release-please-manifest.json, CHANGELOG.md, and version.txt
• Regular PR test: monitor Cloudflare endpoint contract #5 merge does not detect release metadata

Summary by CodeRabbit

• Chores
  • Improved release change detection to more reliably identify files modified between commits.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 55d9ca2a-7a5a-41be-9ae8-6945e220f9c8

📥 Commits

Reviewing files that changed from the base of the PR and between 0b636aa and 2140177.

📒 Files selected for processing (1)

• .github/workflows/release.yml

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📝 Walkthrough

Walkthrough

The release workflow now detects changed files by comparing the previous commit with GITHUB_SHA.

Changes

Release detection

Layer / File(s)	Summary
Compare commits for release files .github/workflows/release.yml	The workflow replaces git show with git diff --name-only between the previous commit and GITHUB_SHA.

Estimated code review effort: 1 (Trivial) | ~2 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the main change: fixing release-change detection for merged release commits.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch agent/fix-release-merge-detection

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