Two root-cause fixes for the "fake done" patterns surfaced while debugging
FN-5475's stuck preflight (it depended on FN-5233, which the board reported
as Done but whose squash had stranded on a sibling fusion/fn-* branch).
1. resolveTaskMergeTarget rejects fusion/fn-* sibling branches as a merge
destination — when a task's baseBranch was inherited from a sibling/dependent
dispatch, the merger detached onto and squashed against that branch instead
of advancing main. New audit event surfaces the steering miss so the
underlying baseBranch-propagation bug stays observable.
2. self-healing findLandedTaskCommit verifies ownership against each grep
candidate's body before attribution. The previous code blindly accepted the
first hit of `git log --grep=FN-XXXX` (which matches the entire commit
message); FN-5441 and FN-5446 were both marked done against an unrelated
FN-5483 commit whose body merely mentioned them in prose. commitOwnedByTask
is also tightened: trailers must be line-anchored and the subject fallback
must match conventional-commit form, not a bare substring.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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