[quality] tide: fork-403 diagnosis failures, refused explanatory comment and the merge-queue head-moved skip are untested

[hivecommons-hive]

Finding

src/plugins/tide.ts has four reachable lines with no unit coverage, all in error/race handling around the merge path:

• explainForkWorkflows (lines 261-262): when compareCommitsWithBasehead or pulls.listFiles fails, the 403 diagnosis is abandoned with a core.debug and the raw merge failure stands.
• explainForkWorkflows (line 280): when the explanatory comment cannot be posted, it is a core.warning and the skip verdict still stands.
• evaluateInQueue (line 316): a head that moves while an unknown mergeable_state is being retried is skipped with head moved during evaluation and no enqueuePullRequest mutation is sent.

Unit evidence: npx vitest run --coverage on origin/main @ 187c5e3 → tide.ts | 98.05 | 94.08 | 100 | 97.94 | 261-262,280,316.
End-to-end evidence: the repository has no e2e suite or e2e coverage artifact (.github/workflows/test.yml runs npm test only), so no e2e claim is made.

Recommendation

Add tests in __tests__/plugins/tide.test.ts (the existing a 403 on a fork pull request describe) for compare 500, listFiles 502 and comment 403, and one in __tests__/plugins/tideMergeQueue.test.ts serving an unknown pull then a pull with a different head sha.

Priority

• Impact: medium — tide is the merge automation; these branches decide between failed and skipped and whether a mutation is sent against a moved head.
• Effort: low

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Filed by quality agent (hold-gated mode)

🐝 Hive Agent: quality | Instance: hosted-available-lke648397-260827-5q9t | SHA: b60162b

— hive: agent=quality backend=copilot model=claude-fable-5.1 copilot=1.0.88

[github-actions]

Please add a kind label with /kind failing-test or /kind cleanup.