Missing on_tool_error inside astream_events when using ToolNode

[hzeus]

I would like to react to exceptions that happen inside tools.

A minimal example of my situation is mostly copied from the ReAct Agent

import asyncio

from langchain_core.tools import tool
from langchain_openai import AzureChatOpenAI
from langgraph.graph import END, START, MessagesState, StateGraph
from langgraph.prebuilt import ToolNode


@tool
def get_weather(location: str):
    """Call to get the current weather."""
    raise ValueError("Location not found")
    return "It's 90 degrees and sunny."


@tool
def get_coolest_cities():
    """Get a list of coolest cities"""
    return "nyc, sf"


tools = [get_weather, get_coolest_cities]
tool_node = ToolNode(tools)


model_with_tools = AzureChatOpenAI(
   ...
).bind_tools(tools)


def should_continue(state: MessagesState):
    messages = state["messages"]
    last_message = messages[-1]
    if last_message.tool_calls:
        return "tools"
    return END


def call_model(state: MessagesState):
    messages = state["messages"]
    response = model_with_tools.invoke(messages)
    return {"messages": [response]}


workflow = StateGraph(MessagesState)

# Define the two nodes we will cycle between
workflow.add_node("agent", call_model)
workflow.add_node("tools", tool_node)

workflow.add_edge(START, "agent")
workflow.add_conditional_edges("agent", should_continue, ["tools", END])
workflow.add_edge("tools", "agent")

app = workflow.compile()


async def run():
    async for event in app.astream_events(
        input={"messages": [("human", "what's the weather in sf?")]}, version="v2"
    ):
        if "tool" in event["event"]:
            print(event["event"])


asyncio.run(run())

When I run this code without the raise ValueError("Location not found") line inside the code, I see two events called on_tool_start and on_tool_end. However, if a add the Exception, I only see on_tool_start.

Reading the Callback events I would have guessed that a on_tool_error event was emitted, but this is not the case. Is there anything I'm doing wrong?

I also tried to dispatch a custom event from inside my tool call. While this basically works I do not know how I would find out the tool_call_id in this case as I think that the ToolNode does not pass this down to the tool implementations.