ci: add dependency audit workflow (#3138)

* ci: add dependency audit workflow

Add a Security Audit workflow with a dependency-audit job. Push/PR/manual
runs pip-audit against a committed --generate-hashes requirements snapshot
(.github/security-audit-requirements.txt) for deterministic CI, while the
weekly scheduled run resolves the runtime + test dependency set live across
the supported Python/OS matrix to surface newly published advisories.

A sync gate (.github/scripts/check_security_requirements.py) fails PRs whose
dependency inputs changed without refreshing the committed snapshot, so the
committed file can't silently drift from pyproject.toml.

Assisted-by: Codex (model: GPT-5, autonomous)

* ci: split dependency audit schedule matrix

Assisted-by: Codex (model: GPT-5, autonomous)

* ci: harden dependency audit sync checks

Assisted-by: Codex (model: GPT-5, autonomous)

* ci: align security workflow python pin

Assisted-by: Codex (model: GPT-5, autonomous)

* ci: refresh dependency audit baseline

Assisted-by: Codex (model: GPT-5, autonomous)

* docs: clarify security snapshot audit

Assisted-by: Codex (model: GPT-5, autonomous)

.github/workflows/security.yml

@@ -0,0 +1,78 @@
+name: Security Audit
+
+permissions:
+  contents: read
+
+on:
+  push:
+    branches: ["main"]
+  pull_request:
+    types: [opened, synchronize, reopened]
+  schedule:
+    - cron: "17 4 * * 1"
+  workflow_dispatch:
+
+jobs:
+  dependency-audit:
+    name: Dependency audit
+    if: ${{ github.event_name != 'schedule' }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          fetch-depth: 0
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@11f9893b081a58869d3b5fccaea48c9e9e46f990 # v8.3.2
+
+      - name: Set up Python
+        uses: actions/setup-python@ece7cb06caefa5fff74198d8649806c4678c61a1 # v6
+        with:
+          python-version: "3.14"
+
+      - name: Check committed audit requirements are current
+        env:
+          DEPENDENCY_DIFF_BASE: ${{ github.event.pull_request.base.sha || github.event.before || '' }}
+          DEPENDENCY_DIFF_HEAD: ${{ github.sha }}
+          GENERATED_REQUIREMENTS: ${{ runner.temp }}/security-audit-requirements.txt
+        run: python .github/scripts/check_security_requirements.py
+
+      - name: Run pip-audit (committed requirements)
+        run: uvx --from pip-audit==2.10.0 pip-audit --disable-pip --require-hashes -r .github/security-audit-requirements.txt --progress-spinner off
+
+  dependency-audit-scheduled:
+    name: Dependency audit scheduled (${{ matrix.os }}, Python ${{ matrix.python-version }})
+    if: ${{ github.event_name == 'schedule' }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, windows-latest]
+        python-version: ["3.11", "3.12", "3.13", "3.14"]
+    steps:
+      - name: Checkout
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@11f9893b081a58869d3b5fccaea48c9e9e46f990 # v8.3.2
+
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@ece7cb06caefa5fff74198d8649806c4678c61a1 # v6
+        with:
+          python-version: ${{ matrix.python-version }}
+
+      # The committed .github/security-audit-requirements.txt is generated with
+      # --universal (resolves across all interpreters/platforms) and is what
+      # push/PR/workflow_dispatch runs audit. The scheduled job instead compiles
+      # per matrix entry with --python-version so it can surface advisories in
+      # wheels that only resolve on a specific interpreter (e.g. 3.11-only) —
+      # coverage the universal file may not exercise. This broadening is
+      # intentional; non-scheduled runs trade that depth for determinism against
+      # the committed snapshot.
+      - name: Compile scheduled audit requirements
+        run: |
+          uv pip compile pyproject.toml --extra test --python-version "${{ matrix.python-version }}" --upgrade --generate-hashes --quiet --output-file "${{ runner.temp }}/spec-kit-audit-requirements.txt"
+
+      - name: Run pip-audit (scheduled live resolution)
+        run: uvx --from pip-audit==2.10.0 pip-audit --disable-pip --require-hashes -r "${{ runner.temp }}/spec-kit-audit-requirements.txt" --progress-spinner off