Use a LangGraph checkpoint saver (e.g., MemorySaver for testing, SqliteSaver or PostgresSaver for production) to automatically save the entire graph state, including the message history, after each step. Restore by passing the same thread_id when invoking the graph.
LangGraph provides a built-in checkpointing mechanism that saves the entire state of the graph (including all messages) after every node execution. To use it, you compile your graph with a checkpointer parameter. The checkpointer stores state keyed by thread_id and can optionally use checkpoint_id for versioning. When you later invoke the graph with the same thread_id, it will resume from the last saved checkpoint, restoring the full message history. This enables multi-turn conversations across different sessions or even across server restarts.