diff --git a/README.md b/README.md
index 5a131860..a4b71e6a 100644
--- a/README.md
+++ b/README.md
@@ -177,7 +177,7 @@ ccs ollama "summarize these logs"
 ## Contribute And Report Safely
 
 - Contributing guide: [CONTRIBUTING.md](./CONTRIBUTING.md)
-- Daily local gate: `bun run format && bun run lint:fix && bun run validate`
+- Daily local gate: `bun run format && bun run lint:fix && bun run validate` (`validate` is the fast path only)
 - Before review or merge confidence: `bun run validate:ci-parity`
 - If PR checks stay queued for more than 10 minutes, assume the self-hosted runner is offline and notify a maintainer instead of retrying blindly
 - Starter work:
diff --git a/scripts/ci-parity-gate.sh b/scripts/ci-parity-gate.sh
index c9b31a53..36b66b28 100755
--- a/scripts/ci-parity-gate.sh
+++ b/scripts/ci-parity-gate.sh
@@ -56,6 +56,8 @@ if git show-ref --verify --quiet "refs/remotes/origin/$BASE_BRANCH"; then
 fi
 
 echo "[i] Running CI-parity local checks..."
+# `set -euo pipefail` above makes every step fail fast. Keep these commands
+# explicit so parity drift is visible when CI changes.
 bun run typecheck
 bun run lint
 bun run format:check
diff --git a/scripts/run-test-bucket.js b/scripts/run-test-bucket.js
index 0f3c0212..da2cdc68 100644
--- a/scripts/run-test-bucket.js
+++ b/scripts/run-test-bucket.js
@@ -4,9 +4,11 @@ const fs = require('node:fs');
 const path = require('node:path');
 const { spawnSync } = require('node:child_process');
 
-const bucket = process.argv[2];
 const rootDir = path.resolve(__dirname, '..');
 const candidateRoots = ['tests/unit', 'tests/integration', 'tests/npm'];
+// Keep this list in sync with any newly added dist-dependent or long-running
+// tests. `tests/unit/scripts/run-test-bucket.test.js` verifies every path here
+// exists so bucket drift fails loudly instead of silently slowing `test:fast`.
 const slowTests = [
   'tests/integration/cursor-daemon-lifecycle.test.ts',
   'tests/integration/proxy/daemon-lifecycle.test.ts',
@@ -23,11 +25,6 @@ const slowTests = [
   'tests/unit/web-server/websearch-routes.test.ts',
 ];
 
-if (!['fast', 'slow', 'all'].includes(bucket)) {
-  console.error('[X] Usage: node scripts/run-test-bucket.js <fast|slow|all>');
-  process.exit(1);
-}
-
 const filePattern = /(\.test\.(c|m)?[jt]s|\.spec\.(c|m)?[jt]s|-test\.(c|m)?[jt]s)$/;
 
 function collectFiles(dir, files = []) {
@@ -51,19 +48,30 @@ function readsBuiltDist(relativePath) {
   return source.includes('dist/');
 }
 
-const discovered = candidateRoots
-  .flatMap((relativeDir) => collectFiles(path.join(rootDir, relativeDir)))
-  .sort();
-const forceSlow = discovered.filter((file) => {
+function getDiscoveredTests() {
+  return candidateRoots
+    .flatMap((relativeDir) => collectFiles(path.join(rootDir, relativeDir)))
+    .sort();
+}
+
+function shouldForceSlow(file) {
   if (file.startsWith('tests/npm/')) {
     return true;
   }
 
   return readsBuiltDist(file);
-});
-const slowSet = new Set([...slowTests, ...forceSlow]);
+}
+
+function getSlowSet() {
+  const discovered = getDiscoveredTests();
+  const forceSlow = discovered.filter((file) => shouldForceSlow(file));
+  return new Set([...slowTests, ...forceSlow]);
+}
 
 function selectBucket(name) {
+  const discovered = getDiscoveredTests();
+  const slowSet = getSlowSet();
+
   return name === 'slow'
     ? [...slowSet].sort()
     : discovered.filter((file) => !slowSet.has(file));
@@ -111,17 +119,40 @@ function runBucket(name) {
   return result.status ?? 1;
 }
 
-if (bucket === 'all') {
-  let exitCode = 0;
+function main(args = process.argv.slice(2)) {
+  const bucket = args[0];
 
-  for (const name of ['fast', 'slow']) {
-    const status = runBucket(name);
-    if (status !== 0) {
-      exitCode = status;
-    }
+  if (!['fast', 'slow', 'all'].includes(bucket)) {
+    console.error('[X] Usage: node scripts/run-test-bucket.js <fast|slow|all>');
+    return 1;
   }
 
-  process.exit(exitCode);
+  if (bucket === 'all') {
+    let exitCode = 0;
+
+    for (const name of ['fast', 'slow']) {
+      const status = runBucket(name);
+      if (status !== 0) {
+        exitCode = status;
+      }
+    }
+
+    return exitCode;
+  }
+
+  return runBucket(bucket);
 }
 
-process.exit(runBucket(bucket));
+if (require.main === module) {
+  process.exit(main());
+}
+
+module.exports = {
+  slowTests,
+  readsBuiltDist,
+  shouldForceSlow,
+  getDiscoveredTests,
+  getSlowSet,
+  selectBucket,
+  main,
+};
diff --git a/tests/unit/scripts/run-test-bucket.test.js b/tests/unit/scripts/run-test-bucket.test.js
new file mode 100644
index 00000000..b4a1213d
--- /dev/null
+++ b/tests/unit/scripts/run-test-bucket.test.js
@@ -0,0 +1,24 @@
+const { describe, expect, test } = require('bun:test');
+const path = require('node:path');
+const bucket = require('../../../scripts/run-test-bucket.js');
+
+describe('run-test-bucket', () => {
+  test('all declared slow tests still exist on disk', () => {
+    for (const relativePath of bucket.slowTests) {
+      const absolutePath = path.resolve(__dirname, '../../../', relativePath);
+      expect(Bun.file(absolutePath).exists()).resolves.toBe(true);
+    }
+  });
+
+  test('forces npm tests into the slow bucket', () => {
+    expect(bucket.shouldForceSlow('tests/npm/cli.test.js')).toBe(true);
+  });
+
+  test('keeps dist-independent javascript tests in the fast bucket', () => {
+    expect(bucket.shouldForceSlow('tests/unit/flag-parsing-simple.test.js')).toBe(false);
+  });
+
+  test('still forces dist-dependent tests into the slow bucket', () => {
+    expect(bucket.shouldForceSlow('tests/unit/config-dir-override.test.js')).toBe(true);
+  });
+});