diff --git a/.github/workflows/codeql.yml b/.github/workflows/codeql.yml
new file mode 100644
index 0000000..dc5d677
--- /dev/null
+++ b/.github/workflows/codeql.yml
@@ -0,0 +1,42 @@
+name: CodeQL
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    # No paths-ignore: every PR must post the status so branch protection
+    # required checks ("Analyze (javascript-typescript)") never stay
+    # stuck in "Expected — Waiting for status to be reported".
+  schedule:
+    - cron: "0 6 * * 1"
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  analyze:
+    name: Analyze (${{ matrix.language }})
+    runs-on: ubuntu-latest
+    permissions:
+      security-events: write
+      actions: read
+      contents: read
+    strategy:
+      fail-fast: false
+      matrix:
+        language: [javascript-typescript, actions]
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
+      - uses: github/codeql-action/init@v3
+        with:
+          languages: ${{ matrix.language }}
+          queries: security-and-quality
+      - uses: github/codeql-action/analyze@v3
+        with:
+          category: "/language:${{ matrix.language }}"
diff --git a/AGENTS.md b/AGENTS.md
index e167e65..005bfa0 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -215,6 +215,7 @@ before any of the rules below.
   shell injection.
 - Do not skip CI hooks (`--no-verify`, `[skip ci]`, `[ci skip]`)
   without an explicit reason in the PR description.
+- Every new test added must run in a CI job, and every new CI job that gates correctness must be added to `main`'s required status checks in the same PR.
 
 ## 15. Accessibility (frontend)