commitOrAmendMergeWithFixes used to swallow every unexpected throw as
`reason: "unknown-phantom"` and the two callers re-threw a bare
"verification fix finalize failed (unknown phantom)" with no operator-
actionable signal. FN-5422-class wedges (preAttemptHeadSha == currentHead
but branchTip ahead with task-trailered commits) couldn't be diagnosed
without re-running.
The catch now records the original error and probes whether the branch
ref itself is authoritative for the task (tip carries Fusion-Task-Id
trailer, base..branch is foreign-contamination-free). When it is — i.e.
the work isn't lost, the integration worktree just didn't advance — the
catch resets rootDir to preAttemptHeadSha so the next merge attempt
starts from a known baseline instead of inheriting partial squash state,
and returns `reason: "branch-ref-ahead-reset"`. The two callers fold
`originalError=` and `branchAuthority=` into the thrown message so the
real cause (diff-volume gate, file-scope, transient git, etc.) is
visible in the run log.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
a2a5db8151