StateSchema

import { z } from "zod";
import { StateSchema, ReducedValue, MessagesValue } from "@langchain/langgraph";

const AgentState = new StateSchema({
  // Prebuilt messages value
  messages: MessagesValue,
  // Basic LastValue channel from any standard schema
  currentStep: z.string(),
  // LastValue with native default
  count: z.number().default(0),
  // ReducedValue for fields needing reducers
  history: new ReducedValue(
    z.array(z.string()).default(() => []),
    {
      inputSchema: z.string(),
      reducer: (current, next) => [...current, next],
    }
  ),
});

// Extract types
type State = typeof AgentState.State;
type Update = typeof AgentState.Update;

// Use in StateGraph
const graph = new StateGraph(AgentState);