feat: add postgres user engine store

src/user_engine/store_records.py

@@ -77,6 +77,11 @@ def store_record_for(value: Any) -> StoreRecord:
     )
 
 
+def composite_record_key(*parts: str | None) -> str:
+    """Return the deterministic composite key used by durable store records."""
+    return _composite_key(*parts)
+
+
 def domain_record_from_store_record(record: StoreRecord) -> Any:
     """Decode a durable-store record payload into its domain dataclass."""
     codec = _CODECS_BY_RECORD_TYPE.get(record.record_type)
@@ -271,7 +276,11 @@ _CODECS = (
         "identity_factors",
         IdentityFactor,
         lambda value: _single_key(value.factor_id),
-        lambda value: {"user_id": value.user_id},
+        lambda value: {
+            "user_id": value.user_id,
+            "scope_type": "registration" if value.registration_id else None,
+            "scope_id": value.registration_id,
+        },
     ),
     StoreRecordCodec(
         "prepared_accounts",