Pre-production code review

Look for reasons this branch should not ship. Verify each finding before giving a verdict.

Phase 1: Pin the healthy point

The user gives you the healthy point: a commit SHA, branch, tag, main, HEAD~5, anything naming a moment when the app worked (production). If they didn't specify one, use main.

Before going further:

1. Confirm it resolves: git rev-parse <healthy-point>.
2. Write the diff command once and reuse it everywhere: git diff <healthy-point>...HEAD. Three dots, so git compares against the merge-base.
3. Confirm the diff is non-empty. A bad ref or empty diff should fail here, not mid-review.

Phase 2: Read the diff and its context