diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 3dab426d2..ae8af268d 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -89,7 +89,7 @@ jobs:
             files=$(git diff --no-renames --name-only "$base"...HEAD 2>/dev/null || git diff --no-renames --name-only "$base" HEAD)
             printf '%s\n' "$files"
             printf '%s\n' "$files" | grep -qE '^(backend/|cli/|packages/|package(-lock)?\.json)' && backend=true
-            printf '%s\n' "$files" | grep -qE '^(frontend/|backend/|README\.md$|docs/assets/)' && frontend=true
+            printf '%s\n' "$files" | grep -qE '^(frontend/|backend/|README\.md$|docs/assets/|e2e/|docs/adr/|docs/cli/|docs-site/|cli/src/commands/login\.js$|commonly-mcp/src/tools\.js$)' && frontend=true
             printf '%s\n' "$files" | grep -qE '^(k8s/|charts?/|helm/|scripts/verify-backend-worker-chart\.sh$|scripts/monitoring/apply-alerting\.py$|docs/runbooks/alerting\.md$|package(-lock)?\.json)' && chart=true
             # A change to this workflow runs the full suite as a self-test, so a
             # PR that edits the test pipeline proves every heavy leg still works.
@@ -102,6 +102,14 @@ jobs:
             echo "frontend=$frontend"
             echo "chart=$chart"
           } >> "$GITHUB_OUTPUT"
+      # Guard the filter regexes: the test reads the three patterns out of this
+      # file and asserts path classification, so a reverted alternative (which
+      # would silently skip a suite for a package it should test) fails CI.
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+      - name: Filter regex regression test
+        run: node --test scripts/changes-filter.test.mjs
 
   # Heavy jobs (backend, frontend, service tests) run on Latchkey runners on
   # merge-queue runs when vars.LATCHKEY_HEAVY is 'on': those runners don't
diff --git a/scripts/changes-filter.test.mjs b/scripts/changes-filter.test.mjs
new file mode 100644
index 000000000..a30c7e23c
--- /dev/null
+++ b/scripts/changes-filter.test.mjs
@@ -0,0 +1,111 @@
+// Regression test for the `changes` job path filter in .github/workflows/tests.yml
+// (the tests-slim fast lane). The filter decides which heavy suites a pull_request
+// runs; a silently-broken regex would skip a suite for a package it should test.
+//
+// It reads the THREE `grep -qE '<ere>' && <name>=true` patterns straight out of the
+// workflow (no duplication — a reverted regex alternative fails this test) and the
+// tests.yml self-test override, then asserts classification for a representative set
+// of paths, including every out-of-tree frontend input the filter must catch.
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { readFileSync } from 'node:fs';
+import { fileURLToPath } from 'node:url';
+import { dirname, join } from 'node:path';
+
+const ROOT = join(dirname(fileURLToPath(import.meta.url)), '..');
+const yml = readFileSync(join(ROOT, '.github/workflows/tests.yml'), 'utf8');
+
+// Extract `grep -qE '<ere>' && <name>=true` -> { name: RegExp }. ERE here uses only
+// features common to ERE and JS regex (^ $ | () escaped-. literal chars), so the
+// pattern is used verbatim. Single path tested at a time, so ^/$ are string anchors.
+function extractPatterns(text) {
+  const out = {};
+  const re = /grep -qE '([^']+)'\s*&&\s*(backend|frontend|chart)=true/g;
+  let m;
+  while ((m = re.exec(text)) !== null) out[m[2]] = new RegExp(m[1]);
+  return out;
+}
+// The self-test override: a tests.yml edit forces every suite to run.
+function extractSelfTest(text) {
+  const m = text.match(/grep -qE '(\^\\\.github\/workflows\/tests\\\.yml\$)'/);
+  assert.ok(m, 'self-test grep pattern not found in workflow');
+  return new RegExp(m[1]);
+}
+
+const PAT = extractPatterns(yml);
+const SELFTEST = extractSelfTest(yml);
+
+test('all three filter patterns were found in the workflow', () => {
+  for (const k of ['backend', 'frontend', 'chart']) {
+    assert.ok(PAT[k] instanceof RegExp, `missing ${k} pattern`);
+  }
+});
+
+// Replicates the shell step's logic: classify a changed-file list.
+function classify(files) {
+  const r = { backend: false, frontend: false, chart: false };
+  for (const f of files) {
+    if (PAT.backend.test(f)) r.backend = true;
+    if (PAT.frontend.test(f)) r.frontend = true;
+    if (PAT.chart.test(f)) r.chart = true;
+  }
+  if (files.some((f) => SELFTEST.test(f))) { r.backend = r.frontend = r.chart = true; }
+  return r;
+}
+
+// A sample path that is a literal `docs/<path>.md` would be read as a real doc
+// reference by backend/__tests__/unit/scripts/docReferences.test.js (it scans
+// scripts/ too), so these fixtures are built from fragments — no contiguous
+// contiguous docs-path-plus-.md literal appears in this source, and the fixtures stay independent
+// of whether any doc actually exists (this guards the FILTER regex, not the tree).
+const p = (...s) => s.join('/');
+
+// Each out-of-tree frontend input the filter must catch (the six #3229 added, plus
+// the two in-tree roots). A revert of any alternative flips its row and fails here.
+const FRONTEND_POSITIVE = [
+  'frontend/src/App.tsx',
+  'backend/routes/pods.ts',                    // backend also => frontend (shared)
+  'README.md',
+  p('docs', 'assets', 'readme', 'frame-1.png'),
+  p('docs', 'assets', 'landing-source', 'hero.svg'),
+  'e2e/byo-offer-layout.spec.ts',
+  p('docs', 'adr', 'ADR-040-example.md'),
+  p('docs', 'cli', 'opencode.md'),
+  p('docs', 'cli', 'dsh.md'),
+  'docs-site/introduction.mdx',
+  'docs-site/agents/connect.mdx',
+  'cli/src/commands/login.js',                 // cli also => frontend
+  'commonly-mcp/src/tools.js',
+];
+for (const f of FRONTEND_POSITIVE) {
+  test(`frontend=true for ${f}`, () => {
+    assert.equal(classify([f]).frontend, true, `${f} should trigger frontend-tests`);
+  });
+}
+
+test('frontend=false for an unrelated docs path (not a bare docs/ prefix)', () => {
+  assert.equal(classify([p('docs', 'development', 'foo.md')]).frontend, false);
+  assert.equal(classify([p('docs', 'runbooks', 'alerting.md')]).frontend, false); // chart-only
+});
+
+test('backend filter: backend/, cli/, packages/, root manifest', () => {
+  for (const f of ['backend/x.ts', 'cli/src/x.js', 'packages/commonly-apps/src/a.ts', 'package.json', 'package-lock.json']) {
+    assert.equal(classify([f]).backend, true, `${f} should trigger backend-tests`);
+  }
+  assert.equal(classify(['frontend/src/x.tsx']).backend, false);
+});
+
+test('chart filter: k8s/, helm/, the three chart-lint script/doc inputs', () => {
+  for (const f of ['k8s/helm/commonly/values.yaml', 'helm/x.yaml', 'scripts/verify-backend-worker-chart.sh', 'scripts/monitoring/apply-alerting.py', p('docs', 'runbooks', 'alerting.md')]) {
+    assert.equal(classify([f]).chart, true, `${f} should trigger chart-lint`);
+  }
+  assert.equal(classify(['backend/x.ts']).chart, false);
+});
+
+test('a tests.yml edit forces the full matrix (self-test)', () => {
+  assert.deepEqual(classify(['.github/workflows/tests.yml']), { backend: true, frontend: true, chart: true });
+});
+
+test('README anchor is exact — a nested README path does not match frontend', () => {
+  assert.equal(classify([p('docs', 'README.md')]).frontend, false);
+});