The hook functions in LangChain middleware, such as before_agent, are not wrapped

[Lesleyblue]

Describe your environment

OS: (e.g, Ubuntu)
Python version: (e.g., Python 3.12.0)
Package version: (e.g., 0.5b0)
GenAI library (e.g. anthropic, openai) and version:

What happened?

When opentelemetry-instrumentation-langchain is enabled, LangChain middleware hooks (before_agent, before_model, after_model, after_agent and their async variants) that are overridden by subclasses never get registered into the LangGraph state graph, causing them to never execute.

Steps to Reproduce

opentelemetry-instrument python test.py

import asyncio
from dotenv import load_dotenv
load_dotenv()
from langchain.agents import create_agent
from langchain.agents.middleware import AgentMiddleware
from langchain.agents.middleware.types import AgentState, ModelRequest, ModelResponse
from langchain_openai import ChatOpenAI
from langchain_core.tools import tool
import os

openai_model: str = os.environ.get("OPENAI_MODEL", "")
openai_base_url: str = os.environ.get("OPENAI_BASE_URL", "")
openai_api_key: str = os.environ.get("OPENAI_API_KEY", "")

CALL_LOG = []

class TestMiddleware(AgentMiddleware):
def before_agent(self, state, runtime):
CALL_LOG.append("before_agent called")
print(">>> before_agent called")
return None

async def awrap_model_call(self, request, handler):
    CALL_LOG.append("awrap_model_call called")
    print(">>> awrap_model_call called")
    return await handler(request)
@tool
def dummy_tool(query: str) -> str:
"""A dummy tool that returns the query."""
return f"Result: {query}"

async def main():
  llm = ChatOpenAI(
  model=openai_model,
  base_url=openai_base_url,
  api_key=openai_api_key, # type: ignore
  temperature=0
  )
  agent = create_agent(
  model=llm,
  tools=[dummy_tool],
  system_prompt="You are a helpful assistant.",
  middleware=[TestMiddleware()],
  name="test_agent",
  )
  
  result = await agent.ainvoke(
      {"messages": [{"role": "user", "content": "Hello"}]},
      config={"configurable": {"thread_id": "test-1"}},
  )
  
  print(f"\nCALL_LOG: {CALL_LOG}")
  print(f"before_agent was called: {'before_agent called' in CALL_LOG}")
  print(f"awrap_model_call was called: {'awrap_model_call called' in CALL_LOG}")
asyncio.run(main())

Expected Result

awrap_model_call called
CALL_LOG: ['awrap_model_call called']
before_agent was called: True
awrap_model_call was called: True

Actual Result

awrap_model_call called
CALL_LOG: ['awrap_model_call called']
before_agent was called: False
awrap_model_call was called: True

Additional context

No response

Would you like to implement a fix?

None

Tip

_{React with 👍 to help prioritize this issue. Please use comments to provide useful context, avoiding +1 or me too, to help us triage it. Learn more here.}