refactor(type hints): add type hints

Author: NicholasGoh

backend/api/core/agent/persistence.py

@@ -1,4 +1,5 @@
 from contextlib import asynccontextmanager
+from typing import AsyncGenerator
 
 import psycopg
 import psycopg.errors
@@ -10,7 +11,9 @@
 
 
 @asynccontextmanager
-async def checkpointer_context(conn_str: str):
+async def checkpointer_context(
+    conn_str: str,
+) -> AsyncGenerator[AsyncPostgresSaver]:
     """
     Async context manager that sets up and yields a LangGraph checkpointer.
 

backend/api/core/dependencies.py

@@ -1,5 +1,5 @@
 from contextlib import asynccontextmanager
-from typing import Annotated
+from typing import Annotated, AsyncGenerator
 
 from fastapi import Depends
 from langchain_mcp_adapters.tools import load_mcp_tools
@@ -36,7 +36,7 @@ def get_engine() -> AsyncEngine:
 
 
 @asynccontextmanager
-async def setup_graph():
+async def setup_graph() -> AsyncGenerator[Resource]:
     async with checkpointer_context(
         settings.checkpoint_conn_str
     ) as checkpointer: