TypeError: Type is not msgpack serializable: Interrupt

[ivanzhu109]

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Example Code

@tool
    def add_user(config: RunnableConfig,
                 tool_call_id: Annotated[str, InjectedToolCallId]
                 ) -> ToolMessage | Command:
        try:
            response = interrupt('Please review the tool call')[0]
            # do add user...
            return tool_success('success', tool_call_id=tool_call_id)
        except Exception as e:
            logger.error(f'{traceback.format_exc()}')
            raise e

agent = create_react_agent(
        model=models.qwen_llm(temperature=chat_co.temperature),
        tools=[UserTool.add_user, UserTool.add_group],
        prompt=system,
        checkpointer=app.state.checkpointer,
        pre_model_hook=trim_message_hook,
        state_schema=NavigateAgentState
    )

async for event in agent.astream_events(state, config=config, stream_mode=["updates", "values"]):
    yield ServerSentEvent(f'{str(event)}').encode()

Description

When the agent specifies a checkpointer and astream_events is used to execute a tool, if the tool raises an interrupt(), throws TypeError: Type is not msgpack serializable: Interrupt.
As a result, the event lacks an output.
With a checkpointer：

Without a checkpointer

System Info

System Information

OS: Darwin
OS Version: Darwin Kernel Version 24.3.0: Thu Jan 2 20:24:06 PST 2025; root:xnu-11215.81.4~3/RELEASE_ARM64_T8103
Python Version: 3.11.13 (main, Jun 5 2025, 08:21:08) [Clang 14.0.6 ]

Package Information

langchain_core: 0.3.66
langchain: 0.3.26
langsmith: 0.3.45
langchain_openai: 0.3.27
langchain_text_splitters: 0.3.8
langgraph_sdk: 0.1.70

Optional packages not installed

langserve

Other Dependencies

async-timeout<5.0.0,>=4.0.0;: Installed. No version info available.
httpx: 0.28.1
httpx>=0.25.2: Installed. No version info available.
jsonpatch<2.0,>=1.33: Installed. No version info available.
langchain-anthropic;: Installed. No version info available.
langchain-aws;: Installed. No version info available.
langchain-azure-ai;: Installed. No version info available.
langchain-cohere;: Installed. No version info available.
langchain-community;: Installed. No version info available.
langchain-core<1.0.0,>=0.3.51: Installed. No version info available.
langchain-core<1.0.0,>=0.3.66: Installed. No version info available.
langchain-deepseek;: Installed. No version info available.
langchain-fireworks;: Installed. No version info available.
langchain-google-genai;: Installed. No version info available.
langchain-google-vertexai;: Installed. No version info available.
langchain-groq;: Installed. No version info available.
langchain-huggingface;: Installed. No version info available.
langchain-mistralai;: Installed. No version info available.
langchain-ollama;: Installed. No version info available.
langchain-openai;: Installed. No version info available.
langchain-perplexity;: Installed. No version info available.
langchain-text-splitters<1.0.0,>=0.3.8: Installed. No version info available.
langchain-together;: Installed. No version info available.
langchain-xai;: Installed. No version info available.
langsmith-pyo3: Installed. No version info available.
langsmith>=0.1.17: Installed. No version info available.
langsmith>=0.3.45: Installed. No version info available.
openai-agents: Installed. No version info available.
openai<2.0.0,>=1.86.0: Installed. No version info available.
opentelemetry-api: Installed. No version info available.
opentelemetry-exporter-otlp-proto-http: Installed. No version info available.
opentelemetry-sdk: Installed. No version info available.
orjson: 3.10.18
orjson>=3.10.1: Installed. No version info available.
packaging: 24.2
packaging<25,>=23.2: Installed. No version info available.
pydantic: 2.11.7
pydantic<3.0.0,>=2.7.4: Installed. No version info available.
pydantic>=2.7.4: Installed. No version info available.
pytest: 8.4.0
PyYAML>=5.3: Installed. No version info available.
requests: 2.32.4
requests-toolbelt: 1.0.0
requests<3,>=2: Installed. No version info available.
rich: 14.0.0
SQLAlchemy<3,>=1.4: Installed. No version info available.
tenacity!=8.4.0,<10.0.0,>=8.1.0: Installed. No version info available.
tiktoken<1,>=0.7: Installed. No version info available.
typing-extensions>=4.7: Installed. No version info available.
zstandard: 0.23.0

[ivanzhu109]

stack

Traceback (most recent call last):
  File "/Users/ivanzhu/job/blacklake/py/xgd-ai-assist/src/agent.py", line 73, in astream
    async for event in agent.astream_events(state, config=config, stream_mode=["updates", "values"]):
  File "/Users/ivanzhu/tools/miniconda3/envs/xgd-ai-assist/lib/python3.11/site-packages/langchain_core/runnables/base.py", line 1404, in astream_events
    async for event in event_stream:
  File "/Users/ivanzhu/tools/miniconda3/envs/xgd-ai-assist/lib/python3.11/site-packages/langchain_core/tracers/event_stream.py", line 1021, in _astream_events_implementation_v2
    await task
  File "/Users/ivanzhu/tools/miniconda3/envs/xgd-ai-assist/lib/python3.11/site-packages/langchain_core/tracers/event_stream.py", line 976, in consume_astream
    async for _ in event_streamer.tap_output_aiter(run_id, stream):
  File "/Users/ivanzhu/tools/miniconda3/envs/xgd-ai-assist/lib/python3.11/site-packages/langchain_core/tracers/event_stream.py", line 204, in tap_output_aiter
    async for chunk in output:
  File "/Users/ivanzhu/tools/miniconda3/envs/xgd-ai-assist/lib/python3.11/site-packages/langgraph/pregel/__init__.py", line 2596, in astream
    async with AsyncPregelLoop(
  File "/Users/ivanzhu/tools/miniconda3/envs/xgd-ai-assist/lib/python3.11/site-packages/langgraph/pregel/loop.py", line 1393, in __aexit__
    return await exit_task
           ^^^^^^^^^^^^^^^
  File "/Users/ivanzhu/tools/miniconda3/envs/xgd-ai-assist/lib/python3.11/contextlib.py", line 745, in __aexit__
    raise exc_details[1]
  File "/Users/ivanzhu/tools/miniconda3/envs/xgd-ai-assist/lib/python3.11/contextlib.py", line 728, in __aexit__
    cb_suppress = await cb(*exc_details)
                  ^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/ivanzhu/tools/miniconda3/envs/xgd-ai-assist/lib/python3.11/site-packages/langgraph/pregel/executor.py", line 209, in __aexit__
    raise exc
  File "/Users/ivanzhu/tools/miniconda3/envs/xgd-ai-assist/lib/python3.11/site-packages/langgraph/checkpoint/postgres/aio.py", line 305, in aput_writes
    params = await asyncio.to_thread(
             ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/ivanzhu/tools/miniconda3/envs/xgd-ai-assist/lib/python3.11/asyncio/threads.py", line 25, in to_thread
    return await loop.run_in_executor(None, func_call)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/ivanzhu/tools/miniconda3/envs/xgd-ai-assist/lib/python3.11/concurrent/futures/thread.py", line 58, in run
    result = self.fn(*self.args, **self.kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/ivanzhu/tools/miniconda3/envs/xgd-ai-assist/lib/python3.11/site-packages/langgraph/checkpoint/postgres/base.py", line 230, in _dump_writes
    return [
           ^
  File "/Users/ivanzhu/tools/miniconda3/envs/xgd-ai-assist/lib/python3.11/site-packages/langgraph/checkpoint/postgres/base.py", line 239, in <listcomp>
    *self.serde.dumps_typed(value),
     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/ivanzhu/tools/miniconda3/envs/xgd-ai-assist/lib/python3.11/site-packages/langgraph/checkpoint/serde/jsonplus.py", line 219, in dumps_typed
    raise exc
  File "/Users/ivanzhu/tools/miniconda3/envs/xgd-ai-assist/lib/python3.11/site-packages/langgraph/checkpoint/serde/jsonplus.py", line 213, in dumps_typed
    return "msgpack", _msgpack_enc(obj)
                      ^^^^^^^^^^^^^^^^^
  File "/Users/ivanzhu/tools/miniconda3/envs/xgd-ai-assist/lib/python3.11/site-packages/langgraph/checkpoint/serde/jsonplus.py", line 639, in _msgpack_enc
    return ormsgpack.packb(data, default=_msgpack_default, option=_option)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: Type is not msgpack serializable: Interrupt

[bedead]

There are two reasons why this could be happening.

1. interrupt requires the use of checkpointer. To quickly test it out u can import memorysaver from langgraph and set it.

graph = graph_builder.compile(checkpointer=MemorySaver())

2. Another reason could be having issue in ur state definition. In langgraph states in lost cases should be of serializable type meaning, they can't be pre initialized objects/classes. In simple words they should only contain attributes with type such as str, int, bool, dict, etc. that helps langgraph seralize these attributes without additional config. But if any other types are used u need to create a custom seralization class of type serde which will be passed to MemorySaver.

# ideal state
class state(TypedDict):
     messages: Annotated[list, add_message]
     data: Dict[str, Any]
     .....

If this doesn't solve the issue, I am open to discuss.