Address code review feedback: improve comments and remove redundant timestamp update

Co-authored-by: lstein <[email protected]>

Author: Copilot

invokeai/app/services/client_state_persistence/client_state_persistence_sqlite.py

@@ -5,8 +5,8 @@
 
 class ClientStatePersistenceSqlite(ClientStatePersistenceABC):
     """
-    SQLite implementation for client persistence.
-    This class stores client data per user to prevent data leakage between users.
+    SQLite implementation for client state persistence.
+    This class stores client state data per user to prevent data leakage between users.
     """
 
     def __init__(self, db: SqliteDatabase) -> None:
@@ -23,8 +23,7 @@ def set_by_key(self, user_id: str, key: str, value: str) -> str:
                 INSERT INTO client_state (user_id, key, value)
                 VALUES (?, ?, ?)
                 ON CONFLICT(user_id, key) DO UPDATE
-                  SET value = excluded.value,
-                      updated_at = CURRENT_TIMESTAMP;
+                  SET value = excluded.value;
                 """,
                 (user_id, key, value),
             )

invokeai/app/services/shared/sqlite_migrator/migrations/migration_26.py

@@ -97,6 +97,7 @@ def _update_client_state_table(self, cursor: sqlite3.Cursor) -> None:
         )
 
         # Migrate existing data to 'system' user
+        # The 'system' user is created by migration 25, so it's guaranteed to exist at this point
         for key, value in existing_data.items():
             cursor.execute(
                 """

tests/app/routers/test_client_state_multiuser.py

@@ -244,7 +244,10 @@ def test_update_existing_key(client: TestClient, admin_token: str):
 
 def test_complex_json_values(client: TestClient, admin_token: str):
     """Test that complex JSON values can be stored and retrieved."""
-    complex_value = '{"params": {"model": "test-model", "steps": 50}, "prompt": "a beautiful landscape"}'
+    import json
+
+    complex_dict = {"params": {"model": "test-model", "steps": 50}, "prompt": "a beautiful landscape"}
+    complex_value = json.dumps(complex_dict)
 
     # Set complex value
     set_response = client.post(