ci(test): perf and scale benchmarks leave the correctness gate

CONTRIBUTING.md

@@ -41,6 +41,20 @@ npm test
 Tests run on [Vitest](https://vitest.dev/). `npm test` runs the unit suite;
 see `package.json` for `test:integration`, `test:coverage`, and friends.
 
+## Test gate
+
+The release gate is a bare `vitest run` (no `--config` flag) — the same
+command the delta gate and CI's checks invoke. It carries the full
+correctness suite and nothing else: wall-clock/scale benchmarks
+(`tests/performance/**`, `tests/critical-performance-benchmark.test.ts`,
+`tests/api/performance-benchmarks.test.ts`) and the two tests whose outcome
+depends on the host machine or network rather than the code
+(`tests/package-size-limit.test.ts` shells out to the `npm` CLI;
+`tests/model-loading.test.ts` makes a real network call to download a model)
+are excluded from it, because a timing threshold or a flaky network call has
+no business failing a correctness check. That whole family runs on demand,
+in its own exclusive slot, via `npm run test:perf`.
+
 ## Standards
 
 - **Strict TypeScript.** No `any` escape hatches to dodge the type checker.