fix(@langchain/langgraph-checkpoint-redis): deserialize checkpointed state

[christian-bromann]

I found a bug where the redis checkpointer wouldn't deserialize the checkpointed state when the graph is interrupted. The state would be something like this:

{
  messages: [
    { lc: 1, type: 'constructor', id: [Array], kwargs: [Object] },
    { lc: 1, type: 'constructor', id: [Array], kwargs: [Object] },
    { lc: 1, type: 'constructor', id: [Array], kwargs: [Object] },
    { lc: 1, type: 'constructor', id: [Array], kwargs: [Object] },
    { lc: 1, type: 'constructor', id: [Array], kwargs: [Object] },
    { lc: 1, type: 'constructor', id: [Array], kwargs: [Object] },
    { lc: 1, type: 'constructor', id: [Array], kwargs: [Object] },
    { lc: 1, type: 'constructor', id: [Array], kwargs: [Object] }
  ]
}

You can reproduce the bug with the following script:

import { z } from "zod";
import { createAgent, tool, createMiddleware, HumanMessage, ToolMessage } from "langchain";
import { Command, MemorySaver } from "@langchain/langgraph";
import { RedisSaver } from "@langchain/langgraph-checkpoint-redis";

const config = { configurable: { thread_id: "thread-123" } };

const getWeather = tool(
  async (input: { city: string }) => {
    return {
      weather: `${input.city} is ${Math.random() > 0.5 ? "sunny" : "rainy"}`,
    };
  },
  {
    name: "get_weather",
    description: "Get the weather for a city",
    schema: z.object({
      city: z.string(),
    }),
  }
);

// const memorySaver = new MemorySaver();
const redisSaver = await RedisSaver.fromUrl(process.env.REDIS_URL!, {
  defaultTTL: 60, // TTL in minutes
  refreshOnRead: true,
});

const interruptMiddleware = createMiddleware({
  name: "memory",
  async beforeModel(state, runtime) {
    console.log("state1 is", state)
    if (ToolMessage.isInstance(state.messages.at(-1))) {
      const result = await runtime.interrupt?.({
        actionRequests: [
          {
            name: "get_weather",
            args: { city: "Tokyo" },
          },
        ],
      })
      console.log("result is", result)
    }
  },
})

const agent = createAgent({
  model: "anthropic:claude-3-7-sonnet-latest",
  tools: [getWeather],
  checkpointer: redisSaver,
  middleware: [interruptMiddleware],
});

const initialState = {
  messages: [new HumanMessage("What is the weather in Tokyo?")],
};

const stream1 = await agent.stream(initialState, config);
for await (const chunk of stream1) {
  // console.log("chunk1 is", chunk)
}

const agent2 = createAgent({
  model: "anthropic:claude-3-7-sonnet-latest",
  tools: [getWeather],
  checkpointer: redisSaver,
  middleware: [interruptMiddleware],
});

const result2 = await agent2.stream(new Command({
  resume: {
    decisions: [
      {
        type: "approve",
      },
    ],
  },
}), config);
for await (const chunk of result2) {
  // console.log("chunk2 is", chunk)
}

console.log(result2);

Solution

This patch ensures that state is deserialized properly.

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