Typecheck tests/ in npm run check tests/ was in no tsconfig include path, so npm run check never looked at it. Vitest transpiles without typechecking, so a green npm test said nothing about whether the specs were type-correct — two type errors sat in tests/memory-leak.test.ts undetected until the previous commit. Adds tsconfig.tests.json, mirroring the existing tsconfig.scripts.json pattern: extends the root config and adds node types for process and globalThis.gc. Kept as a separate program rather than widening the root include so node types do not leak into the src build. Verified by planting a deliberate type error in tests/setup.ts and confirming npm run check fails on it. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011gaCkV6CD5uR1SJpq3BPss - #103