When a branch contained commits already on main (duplicate cherry-picks),
the merger's local squash collapsed to an empty commit. The merger then
recorded that empty commit's SHA on mergeDetails.commitSha. The actual
content landed later on main as a different SHA via PR merge, but the
task kept pointing at the orphaned empty commit.
Symptom: TaskCard showed "N files changed" (falling back to
task.modifiedFiles), but the Changes tab in the modal showed nothing
because the API hit `git diff sha^..sha` on the empty commit and
returned no files.
Two fixes:
1. merger.ts: detect empty squash commits and skip storing commitSha,
logging clearly. recoverInterruptedMergingTasks → findLandedTaskCommit
already exists to backfill the right SHA when the real commit lands;
a missing commitSha is a known fallback path the UI already handles.
2. TaskChangesTab.tsx: when the API returns no files for a done task,
fall back to task.modifiedFiles (paths only, no patches) with a clear
note. Mirrors the existing 3-tier fallback in TaskCard.tsx:1090-1124
so card and modal always agree.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
85ba1071bd