LESSON 176 / 215·2 min readIntermediate

LangGraph

ReferenceReference guide

Words made simple

A few useful meanings before you read the explanation.

Deterministic: Following steps or rules defined by code. The model does not decide which step should run next in a deterministic workflow.
State: The data describing where a workflow is now, what it already knows, and what still needs to happen.
Checkpoint: A saved snapshot of workflow progress that can help it continue later.

More words from this lesson

Durable: Able to retain progress and recover across interruptions. Durable workflows require appropriate storage and retry behavior.
Idempotency: Making a repeated request have the same intended business effect as one request. It helps avoid duplicate submissions or payments.
Authorization: Checking what that identity is allowed to read or do. Being logged in does not grant access to every record.
Trace: A linked record of the steps in one request, including model calls, retrieval and tools. It helps locate delays or failures.

Nodes are steps that perform work, edges choose what runs next, and state carries the information needed by those steps.
Nodes can be ordinary code or model calls, so the graph can be deterministic or hybrid.

It saves execution progress for later continuation or recovery.
It is not automatically long-term user memory or a transaction coordinating all external effects.
Production needs durable storage and authorized thread ownership.

Explicit state contracts, safe concurrent updates, durable checkpoints, version migrations, authenticated resume, bounded retries/deadlines, idempotent side effects, and redacted tracing.
I also define how pending runs survive deployment and how uncertain external writes are reconciled.

The interrupted node may restart, so a send before the interrupt can execute again.
I move sending behind validated approval into an idempotent business operation and reconcile the send key/receipt on retries.

PAUSE & RECALL