Add a Postgres checkpointer to a LangGraph agent for durable cross-session state

Steps

1. Install langgraph-checkpoint-postgres: pip install langgraph-checkpoint-postgres
2. Import AsyncPostgresSaver and create it from a connection string: checkpointer = AsyncPostgresSaver.from_conn_string('postgresql://...')
3. Call await checkpointer.setup() once on first run to create required checkpoint tables in the database
4. Pass the checkpointer into your compiled graph: graph = builder.compile(checkpointer=checkpointer)
5. Invoke the graph with a config dict containing a thread_id: graph.invoke(input, config={'configurable': {'thread_id': 'user-123'}})
6. For horizontal scaling, multiple server instances can safely share the same Postgres checkpoint store concurrently