The project's no-unused-vars only ignores all-underscore names (/^_+$/u); `_bp` in the @vueuse/core useBreakpoints mock failed it. Latent since Task 3 — masked because the whole-codebase `pnpm lint` stylish formatter OOMs (RangeError on the legacy-code message volume) and emitted no results. Scoped errors-only lint surfaced it. 21/21 specs still green. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>