Validated: check-api-typecheck.mjs OK (289 pre-existing, all frozen), typecheck:core clean, 8/8 check-api-typecheck.test.ts pass. Spot-checked two of the six fixes directly — the webhooks/[id]/test/route.ts duplicate import is confirmed removed (real ESM defect), and the volcengine-plan strict-boolean-narrowing fix (`validation.success === false` vs `!validation.success`) is behaviorally identical since `.success` is a strict boolean. This unblocks every other open PR into release/v3.8.51 that was landing red on the new API Route Typecheck gate — including #12085.
Boarded in a combined worktree: typecheck:core, check:dashboard-typecheck, check:file-size, check:changelog-integrity, check:complexity, check:cognitive-complexity, check:cycles, check-deps all green. Clean, self-contained addition (5 new files, 0 modifications to existing code) that mirrors the existing dashboard-typecheck baseline-ratchet pattern. Thanks for closing a real coverage gap — API routes had no dedicated typecheck gate.
