Regeneration-Prompt: |
Investigate the unrelated failures in `src/infra/git-commit.test.ts` that started blocking other prep and gate flows. The real-checkout assertions were failing whenever the current branch ref lived only in `.git/packed-refs`, because `resolveCommitHash()` only followed loose ref files under `refs/heads/*` even though worktrees and packed refs are common in this repo. Keep the existing safety checks that reject traversal from crafted HEAD contents, but fall back to reading an exact ref match from `packed-refs` in the common git dir when the loose ref is missing. Add a deterministic regression test that simulates a worktree checkout with `commondir` and only a packed branch ref so the test no longer depends on the local repository state.
