Add verifyCommitOnMain() check in HandleMerged to ensure the polecat's
commit is actually on main before allowing cleanup. This prevents work
loss when:
- MERGED signal is for a stale MR
- Merge attempt failed after signal was sent
- MR was already merged via different path
The verification uses git merge-base --is-ancestor to confirm the
polecat's HEAD is reachable from main.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
c28a0d5c51