Reuse Check (Polar)

The handle is the diff. The evidence is new code that duplicates something the repo already has, with the import that replaces it.

This is the most common substantive comment in Polar reviews: 84 of ~1,100 human review comments from Feb to Aug 2026 point at an existing helper the author did not know about. It is also the one category where grep beats a human reviewer, and it got worse once agents started writing the code, because an agent that does not search first writes its own helper.

Scope

Run on any diff that adds a function, constant, Annotated type, validator, enum, model property, repository method, React component, or hook. Skip deletions, renames, config and lockfiles.

Owned elsewhere: agent noise → slop-check; API contract → api-surface-review; deploy safety → ship-safety; billing behaviour → billing-review.