Getting UnreachableNodeError error when using Command

[SaM-0777]

I am following this tutorial https://www.youtube.com/watch?v=6BJDKf90L9A&t=83s on how to use Command (The tutorial is in python but I am doing it in TypeScript)

This is my code

import type { Context } from "hono";
import { ChatGroq } from "@langchain/groq";
import { tool } from "@langchain/core/tools";
import { END, START, StateGraph, MessagesAnnotation } from "@langchain/langgraph";
import { ToolNode } from "@langchain/langgraph/prebuilt";
import { Command } from "@langchain/langgraph";
import { z } from "zod";


export async function agentTest(c: Context) {
  const model = new ChatGroq({
    apiKey: Bun.env.GROQ_API_KEY,
    model: "llama-3.1-8b-instant",
    temperature: 0,
  });

  const tools = [
    tool(
      async ({ location }: {location: string}) => {
        if (location.toLowerCase().includes("sf") || location.toLowerCase().includes("san francisco")) {
          return "The weather in San Francisco is 70 degrees and sunny";
        }
        return "It's degrees and sunny.";
      },
      {
        name: "get_weather",
        description: "Get the weather by city",
        schema: z.object({
          location: z.string(),
        }),
      }
    )
  ]

  const toolNode = new ToolNode(tools);
  const modelWithTools = model.bindTools(tools);

  async function callModel(state: typeof MessagesAnnotation.State) {
    const messages = state.messages;
    const response = await modelWithTools.invoke(messages);
    let nextNode: string = END;
    
    if (response.tool_calls?.length) {
      nextNode = "tools";
    };
    
    return new Command({
      goto: nextNode,
      update: {
        messages: [response],
      },
      
    });
  }

  const workflow = new StateGraph(MessagesAnnotation)
    .addNode("agent", callModel)
    .addNode("tools", toolNode)
    .addEdge(START, "agent")
    .addEdge("tools", "agent")
  ;
  
  const agent = workflow.compile();

  const response = await agent.invoke({
    messages: [
      { role: "human", content: "What is the weather in sf?" }
    ]
  }, {
    debug: true
  });

  console.log(response);

  return c.json(response, 200);
}

Here I am getting this error

3 |     constructor(message, fields) {
4 |         let finalMessage = message ?? "";
5 |         if (fields?.lc_error_code) {
6 |             finalMessage = `${finalMessage}\n\nTroubleshooting URL: https://js.langchain.com/docs/troubleshooting/errors/${fields.lc_error_code}/\n`;
7 |         }
8 |         super(finalMessage);
            ^
UnreachableNodeError: Node `tools` is not reachable.

If you are returning Command objects from your node,
make sure you are passing names of potential destination nodes as an "ends" array
into ".addNode(..., { ends: ["node1", "node2"] })".

Troubleshooting URL: https://js.langchain.com/docs/troubleshooting/errors/UNREACHABLE_NODE/

      at new BaseLangGraphError (D:\App Development\agents\reddit\node_modules\@langchain\langgraph\dist\errors.js:8:9)
      at new UnreachableNodeError (D:\App Development\agents\reddit\node_modules\@langchain\langgraph\dist\errors.js:141:9)
      at validate (D:\App Development\agents\reddit\node_modules\@langchain\langgraph\dist\graph\graph.js:298:23)
      at compile (D:\App Development\agents\reddit\node_modules\@langchain\langgraph\dist\graph\state.js:272:14)
      at D:\App Development\agents\reddit\src\test.ts:63:26
      at agentTest (D:\App Development\agents\reddit\src\test.ts:10:33)
      at D:\App Development\agents\reddit\node_modules\hono\dist\compose.js:30:23
      at dispatch (D:\App Development\agents\reddit\node_modules\hono\dist\compose.js:8:32)
      at D:\App Development\agents\reddit\node_modules\hono\dist\middleware\logger\index.js:39:11
      at logger2 (D:\App Development\agents\reddit\node_modules\hono\dist\middleware\logger\index.js:34:33)

How to fix this error?

[vbarda]

you'd need to do this (per the error message)

If you are returning Command objects from your node,
make sure you are passing names of potential destination nodes as an "ends" array
into ".addNode(..., { ends: ["node1", "node2"] })".

const workflow = new StateGraph(MessagesAnnotation)
    .addNode("agent", callModel, { ends: ["tools", END] })

[SaM-0777]

It works...

Thanks