diff --git a/.gitea/workflows/test_pr.yml b/.gitea/workflows/test_pr.yml
index 0992795..c277fa5 100644
--- a/.gitea/workflows/test_pr.yml
+++ b/.gitea/workflows/test_pr.yml
@@ -37,9 +37,28 @@ jobs:
           # do NOT bind the container port to the host to avoid port conflicts on the runner
           docker run -d --name semapform-test semapform-api:test-pr sleep infinity
 
-      - name: Verify python module imports
+      - name: Start server in container and smoke test HTTP (in-container)
         run: |
-          docker exec semapform-test python -c "import api_service; print('import ok')"
+          # start the server inside the container
+          docker exec -d semapform-test uv run uvicorn api_service:app --host 0.0.0.0 --port 8001
+
+          # send a POST request to /api/validate-signature with signature="ST 250 U42 (15)"
+          docker exec semapform-test python - << 'PY'
+            import time, urllib.request, sys
+            url = 'http://127.0.0.1:8001/api/validate-signature?signature=ST%20250%20U42%20%2815%29'
+            for _ in range(20):
+                try:
+                    req = urllib.request.Request(url, method='POST')
+                    r = urllib.request.urlopen(req, timeout=3)
+                    print('status', r.status)
+                    print(r.read().decode())
+                    if 200 <= r.status < 300:
+                        sys.exit(0)
+                except Exception:
+                    time.sleep(1)
+            print('failed')
+            sys.exit(1)
+          PY
 
       - name: Start server in container and smoke test HTTP (in-container)
         run: |
diff --git a/api_service.py b/api_service.py
index ceca917..6c2662f 100644
--- a/api_service.py
+++ b/api_service.py
@@ -30,6 +30,7 @@ def _get_catalogue():
     if cat is None:
         # import inside function to avoid expensive work during module import
         from bibapi import catalogue as _catalogue
+
         cat = _catalogue.Catalogue()
     return cat