Avoid dismissing approvals on restacks alone

[lunelson]

Summary

• Avoid dismissing approvals solely because restacking/rebasing rewrote commit IDs
• Defer rewritten-history cases to the existing range-diff stale-check logic
• Add self-test coverage for safe restacks and changed patch series

Tests

• npm ci
• npx renovate-config-validator
• .github/actions/dismiss-stale-approvals/self-test.sh

[cursor]

PR Summary

Medium Risk
Changes approval-staleness logic in the GitHub Action, which can affect whether PR approvals are dismissed; mistakes could leave stale approvals or cause unnecessary dismissals. Workflow checkout logic also changes which code is tested/executed in PR vs reusable-workflow contexts.

Overview
Stops treating "approval commit is not an ancestor of HEAD" as automatic staleness in check-manual-merge-resolutions.sh; rewritten history (rebase/restack) now defers to the existing git range-diff check unless merge-base itself errors (which now propagates as non-zero).

Expands self-test.sh to cover the new rewritten-history behavior (safe restack vs changed patch series via range-diff) and to verify merge-base failures bubble up.

Updates preflight-stale-approvals.yml so pull_request events checkout the action from the PR head SHA, while other events continue checking out from the reusable workflow ref.

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[augmentcode]

🤖 Augment PR Summary

Summary: This PR refines the “dismiss stale approvals” composite action to avoid invalidating reviews due to restacks/rebases that rewrite commit SHAs.

Changes:

• Updates check-manual-merge-resolutions.sh so “approval commit is not an ancestor of HEAD” no longer marks approvals stale by itself.
• Defers rewritten-history situations to the existing git range-diff-based staleness check.
• Expands self-test.sh coverage to validate that safe rewrites stay non-stale, while changed patch series are still detected as stale via range-diff.

Technical Notes: The action now treats “non-ancestor” as informational (common after rebases) and relies on range-diff output to decide whether the reviewed patch series materially changed.

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[lunelson]

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