diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 54d4f784..c58520b7 100644
--- a/CONTRIBUTING.md
+++ b/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.
diff --git a/package.json b/package.json
index f07bb94c..f5a0325d 100644
--- a/package.json
+++ b/package.json
@@ -88,7 +88,7 @@
     "test:watch": "NODE_OPTIONS='--max-old-space-size=8192' vitest --config tests/configs/vitest.unit.config.ts",
     "test:coverage": "NODE_OPTIONS='--max-old-space-size=8192' vitest run --config tests/configs/vitest.unit.config.ts --coverage",
     "test:unit": "NODE_OPTIONS='--max-old-space-size=8192' vitest run --config tests/configs/vitest.unit.config.ts",
-    "test:perf": "vitest run tests/unit/performance --reporter=basic",
+    "test:perf": "vitest run --config tests/configs/vitest.perf.config.ts",
     "test:integration": "NODE_OPTIONS='--max-old-space-size=8192' vitest run --config tests/configs/vitest.integration.config.ts",
     "test:semantic": "NODE_OPTIONS='--max-old-space-size=8192' vitest run --config tests/configs/vitest.semantic.config.ts",
     "test:all": "npm run test:unit && npm run test:integration",
diff --git a/tests/configs/vitest.perf.config.ts b/tests/configs/vitest.perf.config.ts
new file mode 100644
index 00000000..ca665dae
--- /dev/null
+++ b/tests/configs/vitest.perf.config.ts
@@ -0,0 +1,56 @@
+import { defineConfig } from 'vitest/config'
+
+/**
+ * Perf/scale + environment-dependent test configuration.
+ *
+ * The exclusive on-demand slot for everything the correctness gate
+ * (`vitest.config.ts`, the config a bare `vitest run` picks up) excludes:
+ * wall-clock/scale benchmarks and the two tests whose outcome depends on
+ * the host machine or network rather than the code. See CONTRIBUTING.md's
+ * "Test gate" section and the exclude list in `vitest.config.ts` (root) for
+ * why each file lives here instead of the gate.
+ *
+ * `include` names this set explicitly — it is the mirror image of the
+ * root config's exclude list, not an independent glob, so the two stay in
+ * sync by inspection. Longer timeouts than the gate's 120s/60s: one case in
+ * tests/critical-performance-benchmark.test.ts measures ~128s of real work.
+ */
+export default defineConfig({
+  test: {
+    globals: true,
+    setupFiles: ['./tests/setup.ts'],
+    environment: 'node',
+
+    // Sequential, single fork — same isolation the gate uses, so a perf
+    // measurement isn't skewed by sibling test contention.
+    pool: 'forks',
+    poolOptions: {
+      forks: {
+        maxForks: 1,
+        minForks: 1,
+        singleFork: true,
+        isolate: true
+      }
+    },
+
+    testTimeout: 300000, // 5 minutes per test (the 128s case plus headroom)
+    hookTimeout: 120000,
+    teardownTimeout: 10000,
+
+    maxConcurrency: 1,
+    fileParallelism: false,
+
+    include: [
+      'tests/performance/**/*.{test,spec}.{js,ts}',
+      'tests/critical-performance-benchmark.test.ts',
+      'tests/api/performance-benchmarks.test.ts',
+      'tests/package-size-limit.test.ts',
+      'tests/model-loading.test.ts'
+    ],
+
+    reporters: process.env.CI ? ['dot'] : ['basic'],
+
+    retry: process.env.CI ? 1 : 0,
+    shard: process.env.VITEST_SHARD
+  }
+})
diff --git a/vitest.config.ts b/vitest.config.ts
index 116ab234..013c3c9b 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -2,9 +2,16 @@ import { defineConfig } from 'vitest/config'
 
 /**
  * Vitest Configuration - Optimized for Memory-Intensive Tests
- * 
+ *
  * Handles ONNX transformer model testing (4-8GB memory requirement)
  * Based on 2024-2025 best practices
+ *
+ * THE CORRECTNESS GATE: this is the config a bare `vitest run` (no
+ * `--config` flag) picks up — the delta gate and CI both invoke it that
+ * way. See CONTRIBUTING.md's "Test gate" section for the full picture.
+ * Wall-clock/scale benchmarks and tests whose outcome depends on the host
+ * machine or network rather than the code are excluded below and run on
+ * demand instead, in their own slot: `npm run test:perf`.
  */
 export default defineConfig({
   test: {
@@ -38,7 +45,29 @@ export default defineConfig({
       'node_modules/**',
       'dist/**',
       'scripts/**',
-      '**/*.browser.test.ts'
+      '**/*.browser.test.ts',
+
+      // Wall-clock/scale benchmark family — timing assertions and scale
+      // sweeps whose pass/fail depends on the host machine's speed, not on
+      // the code. Whole files only (a file that mixes correctness describes
+      // with a perf describe stays in the gate). Run on demand via
+      // `npm run test:perf`, which targets exactly this list.
+      'tests/performance/**',
+      'tests/critical-performance-benchmark.test.ts',
+      'tests/api/performance-benchmarks.test.ts',
+
+      // Environment-dependent by construction, not timing-based:
+      // package-size-limit shells out to the `npm` CLI (not guaranteed
+      // present — the functional gate lane is Bun-only host-mode with no
+      // Node.js runtime) and parses npm-version-specific `npm pack` notice
+      // text; model-loading's "Real Model Download Integration" case makes
+      // a genuine, unmocked network call to HuggingFace (its own header
+      // says "Uses REAL transformer models - NO MOCKING"), and the whole
+      // file imports `../src/embeddings/model-manager.js`, which no longer
+      // exists anywhere under src/ — neither belongs in a gate that must be
+      // deterministic.
+      'tests/package-size-limit.test.ts',
+      'tests/model-loading.test.ts'
     ],
     
     // REPORTERS: Dot for CI, verbose for local