PR Review

Review the branch's change surface, not the whole repository.

1. Establish the diff: git diff <base>...HEAD (and git diff <base> when the working tree carries uncommitted changes that belong to the branch). The base branch is named by the caller; fall back to main.
2. Review every changed hunk for correctness: wrong results on edge inputs, unhandled error paths, and behavior that contradicts the function's name or callers.
3. Check test coverage for the changed behavior: new logic without a test exercising its edge cases is a finding.
4. Check documentation the diff made stale: statements in README or docs that were true on the base branch and are false after the change.
5. Report every defect found, each with a severity; include minor and informational findings. Do not report defects in files the branch did not touch — they are outside the pull request.