diff --git a/.gitea/workflows/ci.yml b/.gitea/workflows/ci.yml
index 0b27866c..aa65e565 100644
--- a/.gitea/workflows/ci.yml
+++ b/.gitea/workflows/ci.yml
@@ -36,6 +36,14 @@ jobs:
         run: npm run lint
         working-directory: frontend
 
+      - name: Assert no banned vi.mock patterns
+        shell: bash
+        run: |
+          if grep -rF "vi.mock('pdfjs-dist'" frontend/src/; then
+            echo "FAIL: banned vi.mock('pdfjs-dist') pattern found — see ADR 012. Use the libLoader prop injection pattern instead."
+            exit 1
+          fi
+
       - name: Run unit and component tests with coverage
         shell: bash
         run: |