createMiddleware

const authMiddleware = createMiddleware({
  name: "AuthMiddleware",
  stateSchema: z.object({
    isAuthenticated: z.boolean().default(false),
  }),
  contextSchema: z.object({
    userId: z.string(),
  }),
  beforeModel: async (state, runtime, controls) => {
    if (!state.isAuthenticated) {
      return controls.terminate(new Error("Not authenticated"));
    }
  },
});

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

const historyMiddleware = createMiddleware({
  name: "HistoryMiddleware",
  stateSchema: new StateSchema({
    count: z.number().default(0),
    history: new ReducedValue(
      z.array(z.string()).default(() => []),
      { inputSchema: z.string(), reducer: (current, next) => [...current, next] }
    ),
  }),
  beforeModel: async (state, runtime) => {
    return { count: state.count + 1 };
  },
});