When using 'interrupt' followed by 'new Command({ resume: ...})', get an undefined message error from LangChain + LangGraph

Question

When I invoke a graph that includes interrupts in one of its nodes, it seems to get into an invalid/ unrecoverable state, with the following error:

        return chatGeneration.message;
                              ^

TypeError: Cannot read properties of undefined (reading 'message')
    at ChatOpenAI.invoke (file:///Users/user/code/lgdemo//node_modules/@langchain/core/dist/language_models/chat_models.js:64:31)

The first encounter of the interrupt appears to go well, but after the second encounter this occurs.

(I include the minimal code to reproduce this in full below the question text.)

The main logic is in approveNode, which contains the interrupt.

• If the user responds with y, it proceeds to the toolsNode which the agentNode requested.
• If the user responds with anything else (e.g. n), it proceeds to END

The issue is that once it proceeds to END, the subsequent call to graph.invoke results in this error.

Another thing that I have tried is to change the logic in approveNode such that:

• If the user responds with y, it proceeds to the toolsNode which the agentNode requested. (same as before)
• If the user responds with anything else (e.g. n), it proceeds to back to agentNode. (this has changed)

(and I change the main graph accordingly to reflect this updated flow)

However, this results in the same error as above, just that it happens after the first interrupt instead of the second interrupt.

Questions:

• Is the workflow that I have defined valid? Is there a better way to structure it?
• What's the underlying cause of this particular error message? (Unfortunately being able to reproduce it hasn't given me clues as to why it occurs)
• Otherwise, how can I implement this such that I get a simple approve/ deny for tool calls going on?

---

References used:

• https://langchain-ai.github.io/langgraphjs/concepts/human_in_the_loop/#approve-or-reject
• https://langchain-ai.github.io/langgraphjs/how-tos/review-tool-calls/

---

Main graph:

const workflow = new StateGraph(MessagesAnnotation)
  .addNode('agent', agentNode)
  .addNode('tools', toolsNode)
  .addNode('approve', approveNode, {
    ends: ['tools', END],
  })
  .addEdge(START, 'agent')
  .addEdge('tools', 'agent')
  .addConditionalEdges('agent', agentRouter, ['approve', END]);
const checkpointer = new MemorySaver();
const graph = workflow.compile({
  checkpointer,
});
const graphConfig = {
  configurable: { thread_id: '0x0004' },
};

Tools, nodes, and routers:

const cmdFooTool = tool(async function(inputs) {
  console.log('===TOOL CMD_FOO===');
  return inputs.name;
}, {
  name: 'CMD_FOO',
  description: 'Invoke when you want to do a Foo.',
  schema: z.object({
    name: z.string('Any string'),
  }),
});
const cmdBarTool = tool(async function(inputs) {
  console.log('===TOOL QRY_BAR===');
  return inputs.name;
}, {
  name: 'QRY_BAR',
  description: 'Invoke when you want to query a Bar.',
  schema: z.object({
    name: z.string('Any string'),
  }),
});
const tools = [cmdFooTool, cmdBarTool];
const llmWithTools = llm.bindTools(tools);

const toolsNode = new ToolNode(tools);

async function agentNode(state) {
  console.log('===AGENT NODE===');
  const response = await llmWithTools.invoke(state.messages);
  console.log('=RESPONSE=',
    '\ncontent:', response.content,
    '\ntool_calls:', response.tool_calls.map((toolCall) => (toolCall.name)));
  return { messages: [response] };
}

async function approveNode (state) {
  console.log('===APPROVE NODE===');
  const lastMsg = state.messages.at(-1);
  const toolCall = lastMsg.tool_calls.at(-1);

  const interruptMessage = `Please review the following tool invocation:
${toolCall.name} with inputs ${JSON.stringify(toolCall.args, undefined, 2)}
Do you approve (y/N)`;

  console.log('=INTERRUPT PRE=');
  const interruptResponse = interrupt(interruptMessage);
  console.log('=INTERRUPT POST=');

  const isApproved = (interruptResponse.trim().charAt(0).toLowerCase() === 'y');
  const goto = (isApproved) ? 'tools' : END;
  console.log('=RESULT=\n', { isApproved, goto });
  return new Command({ goto });
}

function hasToolCalls(message) {
  return message?.tool_calls?.length > 0;
}

async function agentRouter (state) {
  const lastMsg = state.messages.at(-1);
  if (hasToolCalls(lastMsg)) {
    return 'approve';
  }
  return END;
}

Simulate a run:

let state;
let agentResult;
let inputText;
let invokeWith;

// step 1: prompt
inputText = 'Pls perform a Foo with name "ASDF".';
console.log('===HUMAN PROMPT===\n', inputText);
invokeWith = { messages: [new HumanMessage(inputText)] };
agentResult = await graph.invoke(invokeWith, graphConfig);

state = await graph.getState(graphConfig);
console.log('===STATE NEXT===\n', state.next);
console.log('=LAST MSG=\n', agentResult.messages.at(-1).content);
console.log('=LAST TOOL CALLS=\n', agentResult.messages.at(-1).tool_calls);

// step 2: interrupted in the 'approve' node, human in the loop authorises
inputText = 'yes'
console.log('===HUMAN INTERRUPT RESPONSE===\n', inputText);
invokeWith = new Command({ resume: inputText });
agentResult = await graph.invoke(invokeWith, graphConfig);

state = await graph.getState(graphConfig);
console.log('===STATE NEXT===\n', state.next);
console.log('=LAST MSG=\n', agentResult.messages.at(-1).content);
console.log('=LAST TOOL CALLS=\n', agentResult.messages.at(-1).tool_calls);

// step 3: prompt
inputText = 'Pls perform a Foo with name "ZXCV".';
console.log('===HUMAN PROMPT===\n', inputText);
invokeWith = { messages: [new HumanMessage(inputText)] };
agentResult = await graph.invoke(invokeWith, graphConfig);

state = await graph.getState(graphConfig);
console.log('===STATE NEXT===\n', state.next);
console.log('=LAST MSG=\n', agentResult.messages.at(-1).content);
console.log('=LAST TOOL CALLS=\n', agentResult.messages.at(-1).tool_calls);

// step 4: interrupted in the 'approve' node, human in the loop does not authorise
inputText = 'no';
console.log('===HUMAN INTERRUPT RESPONSE===\n', inputText);
invokeWith = new Command({ resume: inputText });
agentResult = await graph.invoke(invokeWith, graphConfig);

state = await graph.getState(graphConfig);
console.log('===STATE NEXT===\n', state.next);
console.log('=LAST MSG=\n', agentResult.messages.at(-1).content);
console.log('=LAST TOOL CALLS=\n', agentResult.messages.at(-1).tool_calls);

// step 5: prompt
inputText = 'Pls perform a Foo with name "GHJK".';
console.log('===HUMAN PROMPT===\n', inputText);
invokeWith = { messages: [new HumanMessage(inputText)] };
agentResult = await graph.invoke(invokeWith, graphConfig);

state = await graph.getState(graphConfig);
console.log('===STATE NEXT===\n', state.next);
console.log('=LAST MSG=\n', agentResult.messages.at(-1).content);
console.log('=LAST TOOL CALLS=\n', agentResult.messages.at(-1).tool_calls);

Full output:

===HUMAN PROMPT===
 Pls perform a Foo with name "ASDF".
===AGENT NODE===
(node:58990) [DEP0040] DeprecationWarning: The `punycode` module is deprecated. Please use a userland alternative instead.
(Use `node --trace-deprecation ...` to show where the warning was created)
=RESPONSE= 
content:  
tool_calls: [ 'CMD_FOO' ]
===APPROVE NODE===
=INTERRUPT PRE=
===STATE NEXT===
 [ 'approve' ]
=LAST MSG=
 
=LAST TOOL CALLS=
 [
  {
    name: 'CMD_FOO',
    args: { name: 'ASDF' },
    type: 'tool_call',
    id: 'call_u7CIyWdTesFATZ5bGG2uaVUZ'
  }
]
===HUMAN INTERRUPT RESPONSE===
 yes
===APPROVE NODE===
=INTERRUPT PRE=
=INTERRUPT POST=
=RESULT=
 { isApproved: true, goto: 'tools' }
===TOOL CMD_FOO===
===AGENT NODE===
=RESPONSE= 
content: The Foo operation has been performed with the name "ASDF". 
tool_calls: []
===STATE NEXT===
 []
=LAST MSG=
 The Foo operation has been performed with the name "ASDF".
=LAST TOOL CALLS=
 []
===HUMAN PROMPT===
 Pls perform a Foo with name "ZXCV".
===AGENT NODE===
=RESPONSE= 
content:  
tool_calls: [ 'CMD_FOO' ]
===APPROVE NODE===
=INTERRUPT PRE=
===STATE NEXT===
 [ 'approve' ]
=LAST MSG=
 
=LAST TOOL CALLS=
 [
  {
    name: 'CMD_FOO',
    args: { name: 'ZXCV' },
    type: 'tool_call',
    id: 'call_kKF91c8G6enWwlrLFON8TYLJ'
  }
]
===HUMAN INTERRUPT RESPONSE===
 no
===APPROVE NODE===
=INTERRUPT PRE=
=INTERRUPT POST=
=RESULT=
 { isApproved: false, goto: '__end__' }
===STATE NEXT===
 []
=LAST MSG=
 
=LAST TOOL CALLS=
 [
  {
    name: 'CMD_FOO',
    args: { name: 'ZXCV' },
    type: 'tool_call',
    id: 'call_kKF91c8G6enWwlrLFON8TYLJ'
  }
]
===HUMAN PROMPT===
 Pls perform a Foo with name "GHJK".
===AGENT NODE===
file:///Users/user/code/lgdemo/node_modules/@langchain/core/dist/language_models/chat_models.js:64
        return chatGeneration.message;
                              ^

TypeError: Cannot read properties of undefined (reading 'message')
    at ChatOpenAI.invoke (file:///Users/user/code/lgdemo//node_modules/@langchain/core/dist/language_models/chat_models.js:64:31)
    at process.processTicksAndRejections (node:internal/process/task_queues:105:5)
    at async RunnableCallable.agentNode [as func] (file:///Users/user/code/lgdemo//test.js:51:20)
    at async RunnableCallable.invoke (file:///Users/user/code/lgdemo//node_modules/@langchain/langgraph/dist/utils.js:79:27)
    at async RunnableSequence.invoke (file:///Users/user/code/lgdemo//node_modules/@langchain/core/dist/runnables/base.js:1274:33)
    at async _runWithRetry (file:///Users/user/code/lgdemo//node_modules/@langchain/langgraph/dist/pregel/retry.js:67:22)
    at async PregelRunner._executeTasksWithRetry (file:///Users/user/code/lgdemo//node_modules/@langchain/langgraph/dist/pregel/runner.js:217:33)
    at async PregelRunner.tick (file:///Users/user/code/lgdemo//node_modules/@langchain/langgraph/dist/pregel/runner.js:45:40)
    at async CompiledStateGraph._runLoop (file:///Users/user/code/lgdemo//node_modules/@langchain/langgraph/dist/pregel/index.js:1296:17)
    at async createAndRunLoop (file:///Users/user/code/lgdemo//node_modules/@langchain/langgraph/dist/pregel/index.js:1195:17) {
  pregelTaskId: '7bd60c12-4beb-54b7-85a7-9bc1461600f5'
}

Node.js v23.3.0