Two compounding bugs surfaced as `feat(FN-XXXX): merge fusion/fn-XXXX`
commits landing on main:
1. The verification-fix finalize path could bind `undefined` to SQLite
parameter 4 (`commitSha`) of `upsertTaskCommitAssociation` under the
parallel-attempt race, failing the merge over a denormalization
write after the commit had already landed. Centralized both
duplicated callsites into a helper that validates each git output
before binding.
2. Four self-healing/aiMergeTask recovery sites copied
`classification.commit.subject` verbatim into
`mergeDetails.mergeCommitMessage`, persisting the tier-3
`merge ${branch}` fallback when it ended up on the landed commit.
New `regenerateBareMergeSubject` helper detects the bare pattern
and rebuilds a descriptive subject via the AI summarizer. Cosmetic
only — the git commit is not amended.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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