M16: isolate acceptance and harden readiness

backend/app/services/data_quality.py

@@ -54,15 +54,9 @@ def _has_open_issue(db: Session, rule_type: str, entity_type: str, entity_id: uu
     )
 
 
-def _next_public_ref(db: Session, prefix: str) -> str:
-    existing = db.execute(select(DataQualityIssue.public_ref)).scalars().all()
-    numbers = [
-        int(ref.rsplit("-", 1)[-1])
-        for ref in existing
-        if ref.startswith(f"{prefix}-") and ref.rsplit("-", 1)[-1].isdigit()
-    ]
-    next_number = (max(numbers) + 1) if numbers else 1
-    return f"{prefix}-{next_number:04d}"
+def _new_scan_ref(prefix: str) -> str:
+    """Generate a stable human-readable prefix with a concurrent-safe suffix."""
+    return f"{prefix}-{uuid.uuid4().hex[:10].upper()}"
 
 
 def _open_issue(
@@ -109,7 +103,7 @@ def _open_issue(
         evidence["previous_decision"] = previous.status
 
     issue = DataQualityIssue(
-        public_ref=_next_public_ref(db, "DQ-SCAN"),
+        public_ref=_new_scan_ref("DQ-SCAN"),
         rule_type=rule_type,
         entity_type=entity_type,
         entity_id=entity_id,