How can I create “time-travel” checkpoints for each message in a LangGraph + FastAPI SSE chat app?

[jamesheavey]

Background

• Backend – FastAPI that runs a LangGraph agent chat and streams events over Server-Sent Events (SSE).
• Frontend – Next.js client that consumes those SSE events and stores user / agent messages in PostgreSQL.

Goal

For every message in the conversation I’d like to save a checkpoint ID that represents the state of the LangGraph before that message is processed.
That would let a user “rewind” (e.g., re-phrase an earlier question, or rerun an agent response) by resetting the graph state to the chosen checkpoint and replaying from there.

Current Idea

Emit two custom events from LangGraph for each turn

• user_checkpoint – state before the user’s new message.
• agent_checkpoint – state after the user message but before the agent reply.

I think this might be possible with get_state_history() but it seems quite clunky.

Questions

1. Is there a simpler or idiomatic way in LangGraph to:

• Capture a checkpoint before a node writes to state, and
• Associate that ID with the subsequent message/event?

An alternative I could try would be to only checkpoint the agent response messages and have the checkpoints represent successful messages. This is less clean in the frontend, but might be much cleaner in the backend.

2. Does LangGraph expose a “initial / empty” checkpoint so I can reset the thread to a clean slate (useful when the very first user message is edited)?

3. Are there alternative patterns (e.g., storing deltas, replaying events, database snapshots) that would achieve the same “editable history” UX with less complexity?

Any pointers, best-practice links, or code samples would be hugely appreciated!