diff --git a/.github/workflows/demo-validation.yml b/.github/workflows/demo-validation.yml
new file mode 100644
index 0000000..58dee71
--- /dev/null
+++ b/.github/workflows/demo-validation.yml
@@ -0,0 +1,75 @@
+name: demo validation
+
+on:
+  pull_request:
+    paths:
+      - ".github/workflows/demo-validation.yml"
+      - ".gitattributes"
+      - "docs/demos/docgen.yaml"
+      - "docs/demos/narration/**"
+      - "docs/demos/animations/**"
+      - "docs/demos/terminal/**"
+      - "docs/demos/recordings/**"
+  push:
+    branches:
+      - main
+    paths:
+      - ".github/workflows/demo-validation.yml"
+      - ".gitattributes"
+      - "docs/demos/docgen.yaml"
+      - "docs/demos/narration/**"
+      - "docs/demos/animations/**"
+      - "docs/demos/terminal/**"
+      - "docs/demos/recordings/**"
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: demo-validation-${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
+jobs:
+  validate:
+    name: A/V, narration, streams, and terminal OCR
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+    env:
+      DOCGEN_GIT_REF: b880ba7a96c35fa32672f217e68c3e3592fb2be1
+    steps:
+      - name: Checkout recordings from Git LFS
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
+        with:
+          lfs: true
+
+      - name: Set up Python
+        uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7
+        with:
+          python-version: "3.11"
+          cache: pip
+
+      - name: Install media validation dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install --yes --no-install-recommends ffmpeg tesseract-ocr
+          python -m pip install --upgrade pip
+          pip install "docgen @ git+https://github.com/jmjava/documentation-generator.git@${DOCGEN_GIT_REF}"
+
+      - name: Validate committed demo artifacts
+        working-directory: docs/demos
+        run: |
+          docgen validate --pre-push 2>&1 | tee "${RUNNER_TEMP}/docgen-validation.log"
+          if grep -E '^WARN \[[^]]+\] ocr_scan:' "${RUNNER_TEMP}/docgen-validation.log"; then
+            echo "Terminal error text or an unavailable OCR engine must fail CI." >&2
+            exit 1
+          fi
+
+      - name: Retain validation log
+        if: always()
+        uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6
+        with:
+          name: docgen-validation-${{ github.run_id }}-${{ github.run_attempt }}
+          path: ${{ runner.temp }}/docgen-validation.log
+          if-no-files-found: error
+          retention-days: 14
diff --git a/libs/tekton-dag-common/tests/test_m17_demo_validation.py b/libs/tekton-dag-common/tests/test_m17_demo_validation.py
new file mode 100644
index 0000000..25cd450
--- /dev/null
+++ b/libs/tekton-dag-common/tests/test_m17_demo_validation.py
@@ -0,0 +1,43 @@
+"""Static acceptance checks for the M17.9 demo validation gate."""
+
+import re
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[3]
+WORKFLOW = ROOT / ".github/workflows/demo-validation.yml"
+
+
+def test_demo_sources_trigger_pre_push_validation():
+    workflow = WORKFLOW.read_text()
+
+    for path in (
+        "docs/demos/docgen.yaml",
+        "docs/demos/narration/**",
+        "docs/demos/animations/**",
+        "docs/demos/terminal/**",
+        "docs/demos/recordings/**",
+    ):
+        assert path in workflow
+
+    assert "docgen validate --pre-push" in workflow
+    assert "lfs: true" in workflow
+
+
+def test_demo_validation_installs_authoritative_media_checks():
+    workflow = WORKFLOW.read_text()
+
+    assert "ffmpeg tesseract-ocr" in workflow
+    assert "A/V, narration, streams, and terminal OCR" in workflow
+    assert "DOCGEN_GIT_REF: b880ba7a96c35fa32672f217e68c3e3592fb2be1" in workflow
+    assert r"grep -E '^WARN \[[^]]+\] ocr_scan:'" in workflow
+    assert "unavailable OCR engine must fail CI" in workflow
+    assert "if-no-files-found: error" in workflow
+
+
+def test_demo_validation_actions_are_immutable():
+    workflow = WORKFLOW.read_text()
+    uses = re.findall(r"^\s*uses:\s*(\S+)", workflow, flags=re.MULTILINE)
+
+    assert uses
+    for action in uses:
+        assert re.fullmatch(r"[^@\s]+@[0-9a-f]{40}", action), action
diff --git a/milestones/milestone-17.md b/milestones/milestone-17.md
index 97da2ef..5a96df5 100644
--- a/milestones/milestone-17.md
+++ b/milestones/milestone-17.md
@@ -77,18 +77,22 @@ regression criteria in `docs/AGENT-REGRESSION.md` are satisfied.
     ShellCheck, actionlint, strict YAML/JSON parsing, both frontend lint/build
     matrices, and staged/package Helm renders.
 
-- [ ] **M17.8 Add supply-chain automation**
+- [x] **M17.8 Add supply-chain automation**
   - Dependabot/Renovate-equivalent updates for actions, npm, Go, Python, Maven,
     and Composer.
   - Add dependency and container scanning; remove known production dependency
     findings; pin CI tools and runtime images by version/digest where practical.
   - Acceptance: no unresolved critical/high production findings without an
     expiring, documented exception.
+  - Evidence: supply-chain run `34974127479` passed filesystem/secret scanning
+    and all three production image gates after the M17.8 hotfix.
 
-- [ ] **M17.9 Enforce demo validation**
+- [x] **M17.9 Enforce demo validation**
   - Run `docgen validate --pre-push` in CI for demo-source changes.
   - Acceptance: A/V drift, narration lint, missing streams, and broken terminal
     recordings fail CI.
+  - Evidence: demo-validation run `34975666059` fetched committed Git LFS
+    recordings and passed stream, A/V drift, narration, and OCR validation.
 
 ## P2 — Test-depth gaps