Use explicit PR head baseline for fork PR branch updates

[Copilot]

push_to_pull_request_branch could not generate incremental patches for fork PRs checked out via refs/pull/<N>/head, because it expected origin/<head.ref> to exist in the base repository. In same-named branch cases, that fallback could also select the wrong base repo ref.

• Record PR checkout baseline

  • Capture the fetched PR head ref/SHA during PR-context checkout.
  • Export it as GH_AW_PR_HEAD_BASE_* for later safe-output patch generation.

• Use explicit incremental base

  • Teach patch and bundle generation to prefer the recorded PR-head baseline over origin/<branch>.
  • Keep the existing origin/<branch> path as a same-repo/backward-compatible fallback.

• Avoid misleading fork guidance

  • Update missing-baseline errors to describe the PR checkout baseline requirement instead of recommending checkout.fetch for fork branches.

• Regression coverage

  • Covers fork PRs without origin/<branch>.
  • Covers fork PRs where the base repo has a same-named branch.
  • Covers safe-output persistence and bundle generation from the recorded PR head.

await generateGitPatch("feature/native_versions", "main", {
  mode: "incremental",
  incrementalBaseRef: "refs/remotes/origin/pr-head",
  incrementalBaseSha: prHeadSha,
});

• Fixes push_to_pull_request_branch cannot update fork PRs after PR-context checkout #56115

[Copilot]

Pull request overview

Adds an explicit PR-head baseline so incremental safe-output patches and bundles work correctly for fork PRs.

Changes:

• Exports PR checkout baseline metadata.
• Prefers the recorded baseline during patch and bundle generation.
• Adds fork and same-named branch regression tests.

Show a summary per file

File	Description
actions/setup/js/checkout_pr_branch.cjs	Records PR-head baseline metadata.
actions/setup/js/checkout_pr_branch.test.cjs	Tests baseline exports.
actions/setup/js/safe_outputs_handlers.cjs	Applies baseline to push artifacts.
actions/setup/js/safe_outputs_handlers.test.cjs	Tests safe-output persistence.
actions/setup/js/generate_git_patch.cjs	Supports explicit incremental patch bases.
actions/setup/js/generate_git_patch.test.cjs	Covers fork and name-collision patches.
actions/setup/js/generate_git_bundle.cjs	Supports explicit incremental bundle bases.
actions/setup/js/generate_git_bundle.test.cjs	Covers fork bundle generation.

Review details

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• Files reviewed: 8/8 changed files
• Comments generated: 2
• Review effort level: Balanced

[Copilot]

Fixed in cd10... — now resolving HEAD^{commit} after checkout and exporting that as GH_AW_PR_HEAD_BASE_SHA instead of the payload/API head.sha.

[Copilot]

Fixed in b997284 — the checkout step now exports GH_AW_PR_HEAD_BASE_PR_NUMBER alongside the baseline, and resolvePRHeadBaselineForPush rejects the recorded baseline unless it matches the effective target PR number (explicit pull_request_number, or the triggering PR/issue context).

[gh-aw-bot]

@copilot PR #56119 is ready for forward progress.

• Please refresh the branch if needed and run the pr-finisher skill before handing back.
• Recent automated review summary: Use explicit PR head baseline for fork PR branch updates #56119 (review)

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[github-actions]

Category: bug; risk: medium; score: 54/100 (impact 25/50, urgency 16/30, quality 13/20); recommended action: batch_review; CI: pending/unknown; review signal: 3 reviews, 1 issue comment.

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