feat(graph): Implement PostgresSaver checkpointer integration

src/ea_chatbot/graph/checkpoint.py

@@ -0,0 +1,44 @@
+import contextlib
+from typing import AsyncGenerator
+from psycopg_pool import AsyncConnectionPool
+from langgraph.checkpoint.postgres.aio import AsyncPostgresSaver
+from ea_chatbot.config import Settings
+
+settings = Settings()
+
+_pool = None
+
+def get_pool() -> AsyncConnectionPool:
+    """Get or create the async connection pool."""
+    global _pool
+    if _pool is None:
+        _pool = AsyncConnectionPool(
+            conninfo=settings.history_db_url,
+            max_size=20,
+            kwargs={"autocommit": True, "prepare_threshold": 0},
+            open=False, # Don't open automatically on init
+        )
+    return _pool
+
+@contextlib.asynccontextmanager
+async def get_checkpointer() -> AsyncGenerator[AsyncPostgresSaver, None]:
+    """
+    Context manager to get a PostgresSaver checkpointer.
+    Ensures that the checkpointer is properly initialized and the connection is managed.
+    """
+    pool = get_pool()
+    # Ensure pool is open
+    if pool.closed:
+        await pool.open()
+        
+    async with pool.connection() as conn:
+        checkpointer = AsyncPostgresSaver(conn)
+        # Ensure the necessary tables exist
+        await checkpointer.setup()
+        yield checkpointer
+
+async def close_pool():
+    """Close the connection pool."""
+    global _pool
+    if _pool and not _pool.closed:
+        await _pool.close()