Harden CardDAV credential and network boundaries

src/govoplan_addresses/backend/router.py

@@ -103,6 +103,7 @@ from govoplan_addresses.backend.service import (
     restore_contact,
     resolve_sync_conflict,
     preview_sync_source,
+    public_address_sync_metadata,
     run_sync_source,
     start_sync_attempt,
     update_address_book,
@@ -217,7 +218,7 @@ def _sync_source_response(sync_source: AddressSyncSource) -> AddressSyncSourceRe
             "last_success_at": sync_source.last_success_at,
             "last_error": sync_source.last_error,
             "last_diagnostic": sync_source.last_diagnostic,
-            "metadata": sync_source.metadata_ or {},
+            "metadata": public_address_sync_metadata(sync_source.metadata_),
             "created_at": sync_source.created_at,
             "updated_at": sync_source.updated_at,
         }