Time Travel & Replay
Graphs fail in the middle. Time travel lets you see the state at that node, patch a field, and replay — the production debugger.
CCTV plus a rewind button. You do not rebuild the store. You scrub to 14:02 and watch the door.
Visual Workflows
Start here — scroll inside each diagram frame to explore, then use + / − to zoom up to 200% if needed.
Overview
Scroll inside the frame to explore · use + / − to zoom up to 200%
Scroll inside the frame to explore · use + / − to zoom up to 200%
Debug a bad route
Scroll inside the frame to explore · use + / − to zoom up to 200%
If classify tagged tech instead of billing, fork from that checkpoint with the right label and replay.
What you do not time-travel
Scroll inside the frame to explore · use + / − to zoom up to 200%
Do not rewind a refund that already hit the bank. Time travel is for state, not for undoing the world.
Key Takeaways
- 1.Time travel reads checkpoint history for a thread: every super-step is a frame you can inspect. get_state shows now. get_state_history lists the past. update_state writes a fork and continues from there.
- 2.This is how you debug 'why did it refund' without re-running the whole ticket from scratch. It is not git. It is an audit log of state. Treat it as sensitive — it contains user messages.
- 3.graph.get_state(config) returns the current snapshot. get_state_history(config) walks checkpoints. update_state(config, values, as_node=...) creates a new checkpoint as if that node had returned those values. Replay by invoking with the checkpoint's id.
- 4.Needs the same checkpointer you used to run.
Learn elsewhere
- →Checkpoints
- →Eval engineering — Phase 19
Real Example
Scenario
Thread ticket-4411 classified as tech. You inspect history, set ticket_type to billing, resume. The billing subgraph runs. The user is still on the same ticket id.
What you would do
In the last module you will print get_state after a pause. Get used to reading the snapshot before you ever fork production threads.
Commands
Commands to Remember
graph.get_state(config) # nowgraph.get_state_history(config) # framesgraph.update_state(config, values) # forkDo not rewind side effects that already happened
Cheat Sheet
Quick recap
quick ref- •History is checkpoints
- •get_state / history
- •update_state forks
- •Not an undo for money
Common Mistakes
- ✕Trying time travel without a checkpointer
- ✕Forking production threads as a habit instead of fixing the route function
- ✕Logging full history (PII) to a shared Slack channel