M16: isolate acceptance and harden readiness

backend/tests/test_data_quality.py

@@ -148,9 +148,7 @@ def test_merge_customers_s2_scenario_rewires_and_audits(ops_client):
     issue = ops_client.get("/api/v1/data-quality/issues/DQ-DEMO-DUPLICATE").json()
     assert issue["status"] == "resolved"
 
-    audit_events = ops_client.get(
-        "/api/v1/audit", params={"action": "customer_merged"}
-    ).json()
+    audit_events = ops_client.get("/api/v1/audit", params={"action": "customer_merged"}).json()
     assert len(audit_events) >= 1
 
     # Already-resolved issue cannot be merged again.
@@ -431,9 +429,7 @@ def test_manual_scan_records_audit_event(ops_client):
     scan = ops_client.post("/api/v1/data-quality/scan")
     assert scan.status_code == 200
 
-    events = ops_client.get(
-        "/api/v1/audit", params={"action": "data_quality_scan_run"}
-    ).json()
+    events = ops_client.get("/api/v1/audit", params={"action": "data_quality_scan_run"}).json()
     assert len(events) >= 1
     assert "created" in events[0]["metadata"]
 
@@ -444,9 +440,7 @@ def _reset_demo(ops_client) -> None:
     # in before making any further authenticated call with the same client.
     response = ops_client.post("/api/v1/demo/reset")
     assert response.status_code == 200, response.text
-    login_response = ops_client.post(
-        "/api/v1/demo/login", json={"role": "operations_manager"}
-    )
+    login_response = ops_client.post("/api/v1/demo/login", json={"role": "operations_manager"})
     assert login_response.status_code == 200, login_response.text
 
 
@@ -548,3 +542,11 @@ def test_rejected_issue_recurrence_links_to_prior_decision(ops_client):
     )
     assert match is not None, "expected a new issue linked back to the rejected one"
     assert match["evidence"]["previous_decision"] == "rejected"
+
+
+def test_scan_public_refs_are_collision_resistant() -> None:
+    from app.services.data_quality import _new_scan_ref
+
+    refs = {_new_scan_ref("DQ-SCAN") for _ in range(1000)}
+    assert len(refs) == 1000
+    assert all(ref.startswith("DQ-SCAN-") and len(ref) == 18 for ref in refs)