ci: add CodeQL advanced setup to scan pull requests before merge

.github/workflows/codeql.yml

@@ -0,0 +1,41 @@
+name: CodeQL
+
+# Advanced setup so CodeQL also runs on pull requests (including from forks),
+# surfacing findings before merge instead of only after a change lands on dev.
+on:
+  push:
+    branches: [dev, main]
+  pull_request:
+    branches: [dev]
+  schedule:
+    - cron: "17 3 * * 1"
+
+permissions:
+  contents: read
+
+jobs:
+  analyze:
+    name: Analyze (${{ matrix.language }})
+    runs-on: ubuntu-latest
+    permissions:
+      security-events: write
+      actions: read
+      contents: read
+    strategy:
+      fail-fast: false
+      matrix:
+        language: [actions, javascript-typescript, python]
+    steps:
+      - name: Checkout
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0  # v7.0.0
+        with:
+          persist-credentials: false
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@8aad20d150bbac5944a9f9d289da16a4b0d87c1e  # v4.36.2
+        with:
+          languages: ${{ matrix.language }}
+          build-mode: none
+      - name: Perform CodeQL Analysis
+        uses: github/codeql-action/analyze@8aad20d150bbac5944a9f9d289da16a4b0d87c1e  # v4.36.2
+        with:
+          category: "/language:${{ matrix.language }}"

docs/security-ci.md

@@ -7,10 +7,9 @@ benefit.
 
 ## What runs, and why
 
-Most checks live in files under `.github/workflows/`. CodeQL is configured
-through GitHub's code scanning default setup, so it appears as a dynamic GitHub
-workflow instead of a checked-in workflow file. They run automatically; you do
-not start them.
+Most checks live in files under `.github/workflows/`. CodeQL uses the
+checked-in advanced configuration in `.github/workflows/codeql.yml`. They run
+automatically; you do not start them.
 
 | Check | What it protects against | Blocks a merge? |
 |---|---|---|
@@ -90,14 +89,9 @@ let the workflows run on one pull request first, then add them here.
 2. Turn on **Dependency graph** (usually on by default for public repos) -- this
    powers Dependency review and Dependabot.
 3. Turn on **Dependabot alerts** and **Dependabot security updates**.
-4. Under **Code scanning**, use **Set up -> Default** for CodeQL. GitHub then
-   runs CodeQL as a dynamic workflow without the fork-token limitations that
-   affect checked-in advanced workflows.
-
-   Do not also add a checked-in CodeQL workflow while default setup is enabled:
-   GitHub rejects advanced CodeQL uploads when default setup is active. If the
-   project later needs an advanced CodeQL workflow, disable default setup first
-   and keep only one CodeQL publishing path active.
+4. Under **Code scanning**, keep **Default setup** disabled. CodeQL is
+   configured by `.github/workflows/codeql.yml`; enabling default setup at the
+   same time causes GitHub to reject uploads from the checked-in workflow.
 
 ## Keeping it current