Investigate a change for duplicated logic, reinvented utilities, and missed reuse of the project's existing helpers, patterns and installed libraries, then report what should have been reused and how. Use when you say "check this PR for duplication", "did we already have a function for this", "is this reinventing something", "why is there a second date formatter", or "review this for reuse before I approve it". Not for a full multi-pillar review pass, use `code-reviewer`.
