fix: DSR export type-cast bug + session rollback on partial failures

- tenant_id kept as string (PostgreSQL handles UUID cast)
- Einwilligungen query uses CAST(:tid AS VARCHAR) for compatibility
- Each data source query wrapped with rollback on failure to prevent
  cascading "transaction aborted" errors

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend-compliance/compliance/services/dsr_export_service.py

@@ -40,7 +40,7 @@ class DSRExportService:
     def aggregate_user_data(self, tenant_id: str, email: str) -> dict[str, Any]:
         """Collect ALL data about a user from all CMP sources."""
         now = datetime.now(timezone.utc)
-        tid = uuid.UUID(tenant_id) if len(tenant_id) > 20 else tenant_id
+        tid = tenant_id  # Keep as string — let PostgreSQL cast
 
         # 1. Banner consents + audit trail
         banner_data: dict[str, Any] = {"banner_consents": [], "audit_trail": []}
@@ -49,6 +49,10 @@ class DSRExportService:
             banner_data = banner_svc.export_for_dsr(tenant_id, email)
         except Exception as e:
             logger.warning("Banner DSR export failed: %s", e)
+            try:
+                self.db.rollback()
+            except Exception:
+                pass
 
         # 2. Einwilligungen (user-based consents)
         einwilligungen: list[dict] = []
@@ -57,7 +61,7 @@ class DSRExportService:
                 SELECT c.id, c.data_point_id, c.granted, c.granted_at, c.revoked_at,
                        c.consent_version, c.source, c.ip_address, c.user_agent, c.created_at
                 FROM compliance_einwilligungen_consents c
-                WHERE c.tenant_id = :tid AND c.user_id = :email
+                WHERE c.tenant_id = CAST(:tid AS VARCHAR) AND c.user_id = :email
                 ORDER BY c.created_at DESC
             """)
             rows = self.db.execute(q, {"tid": tid, "email": email}).fetchall()
@@ -83,6 +87,10 @@ class DSRExportService:
                 einwilligungen.append(entry)
         except Exception as e:
             logger.warning("Einwilligungen export failed: %s", e)
+            try:
+                self.db.rollback()
+            except Exception:
+                pass
 
         # 3. DSR requests by this user
         dsr_requests: list[dict] = []
@@ -104,6 +112,10 @@ class DSRExportService:
                 dsr_requests.append(entry)
         except Exception as e:
             logger.warning("DSR requests export failed: %s", e)
+            try:
+                self.db.rollback()
+            except Exception:
+                pass
 
         return {
             "export_date": now.isoformat(),