What it's for
A chain is a list: A, then B, then C. Real products retry, wait for a person, fan out, or pick up two days later. That's a graph.
Jobs
Support
Where is order 4421?
One lookup, empty, then "I don't know." The list cannot come back.
Lookup misses. Decide loops to a better query, finds the order, answers. Or it hands off to a human.
Approvals
A $240 refund is over policy. It needs a manager.
Auto-refund or refuse. A list has no pause. The human is a different request.
Draft the refund, yield, sit for hours or days. The manager says yes. The same run continues and the money moves.
Research
What's our Q3 churn by plan?
One search, one write. It ships a thin answer because the list already moved on.
Search, judge, rewrite the query, search again, then write. The loop is the work.
Fan-out
Summarize every open ticket before the 9am huddle.
One giant prompt, or twelve calls in a line. Slow, and one bad ticket poisons the rest.
Split into twelve children in the same step. Each summarizes its ticket. The parent joins them into one brief.
Coding
The checkout test is flaky. Fix it.
One shot of code. Usually wrong. You start a new call to try again.
Edit, run tests, fail, edit, pass, stop. There is no Agent class. The loop is the agent.
Durable work
They come back two days later. "Also refund the mug."
A new call. Thursday never happened.
Same thread. The checkpointer is the cursor through this run. The Store still knows they like terse replies.
Patterns
Use it when the work retries, waits, fans out, or lives across days. Skip it for one LLM call or a straight A→B→C chain.
Two kinds of memory. The checkpointer is the cursor through this run — the refund that sits overnight. The Store is what should still be true next week — Tuesday still knows they like terse replies.
| Checkpointer | Store | |
|---|---|---|
| Scope | This run / this thread | This user / this tenant, next week |
| Holds | Snapshots you can replay | Notes you put and get later |
| Reach for it | Pause, resume, time travel | A brand-new thread should still know yesterday's tone |
FAQ
No. If the path is A then B then C and it never comes back, stay on a chain. The ticket that looks again, the refund that waits, the standup brief — those retry, pause, or fan out. That's when a graph earns its keep.
You can compile without one. You need one the moment the refund sits overnight, or Tuesday picks up the same thread. Production graphs almost always have one.
Supervisor: one node delegates; specialists are tools (or subgraphs). Swarm: peers hand off. The standup brief is fan-out, not a swarm — don't reach for a team when a split-and-join will do. Step both in the lab.