diff --git a/.github/workflows/ddd_tests.yml b/.github/workflows/ddd_tests.yml
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+name: Run DDD tests
+
+on:
+  pull_request:
+    branches:
+      - "**"
+
+# The DDD rewrite (tests/) defines SQLModel table classes that map to the same
+# physical tables as the legacy backend models. Both sets share the one global
+# SQLModel.metadata, so they cannot be imported into the same pytest process —
+# hence this runs as a separate workflow from unit_tests.yml until the legacy
+# models are retired. It also covers the Lambda packaging linter
+# (tests/test_lambda_packaging.py). Its DB is spawned in-process by
+# pytest-postgresql, so no `services: postgres` and no env secrets are required,
+# and it runs independently of (and in parallel with) the legacy unit tests.
+jobs:
+  ddd-tests:
+    name: DDD tests (Docker)
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Build test image
+        run: docker build -f Dockerfile.test -t model-test .
+
+      - name: Run DDD tests
+        run: |
+          docker run --rm \
+            --network host \
+            model-test pytest -vv tests/