Python: [Bug]: Callable class middleware raises `AttributeError` instead of `MiddlewareException` when `__call__` has fewer than 2 parameters

[PreethamNoelP]

Description

What happened?
Passing a callable class instance (a class with __call__ but fewer than 2 parameters) as middleware raises:
AttributeError: 'BadMiddleware' object has no attribute '__name__'

The error gives zero indication of what the user did wrong.

What did you expect to happen?
A clear MiddlewareException:
"Middleware function must have at least 2 parameters (context, call_next), but BadMiddleware has 1."

Steps to reproduce:

1. Create a callable class whose __call__ takes only 1 parameter (missing call_next)
2. Pass an instance to Agent(..., middleware=[BadMiddleware()])
3. Constructor raises AttributeError instead of MiddlewareException

Code Sample

from unittest.mock import AsyncMock
from agent_framework import Agent

class BadMiddleware:
    async def __call__(self, ctx):   # missing `call_next` second parameter
        pass

agent = Agent(client=AsyncMock(), middleware=[BadMiddleware()])

Error Messages / Stack Traces

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File ".../agent_framework/_middleware.py", line 1263, in __init__
    middleware_list = categorize_middleware(middleware)
  ...
  File ".../agent_framework/_middleware.py", line 1501, in _determine_middleware_type
    f"Cannot determine middleware type for function {middleware.__name__}. "
AttributeError: 'BadMiddleware' object has no attribute '__name__'

Package Versions

agent-framework-core: 1.9.0

Python Version

Python 3.10 – 3.14 (all versions affected)

Additional Context

Root Cause:
_determine_middleware_type() in _middleware.py uses middleware.__name__ bare at lines 1474, 1487, and 1501. Functions/lambdas always have __name__, but callable class instances do not — instance.__name__ raises AttributeError. The first occurrence is silently swallowed by except Exception: pass, and the second (outside the try/except) propagates uncaught.

Proposed Fix (3 lines):
Replace middleware.__name__ with getattr(middleware, '__name__', type(middleware).__name__) at lines 1474, 1487, and 1501 in _middleware.py. Purely additive — no behaviour changes for existing working paths.

A regression test should be added to test_middleware_with_agent.py covering callable class instances with insufficient parameters.

[PreethamNoelP]

I can raise a PR for this fix if the team agrees with the approach.

[github-actions]

🤖 Automated triage reproduction notes (agent-authored — trust but verify)

Agent analysis

Repro: _determine_middleware_type() in python/packages/core/agent_framework/_middleware.py raises AttributeError instead of MiddlewareException when passed a callable class instance whose __call__ has fewer than 2 parameters. The bare middleware.__name__ at lines 1474, 1487, and 1501 fails for class instances (which lack __name__); the AttributeError at line 1474 is silently swallowed by the except Exception block, then line 1501 raises it uncaught. Minimal repro: define a class with async def __call__(self, ctx) and call _determine_middleware_type(BadMiddleware()) — expects MiddlewareException, gets AttributeError. Fix all three occurrences by replacing middleware.__name__ with getattr(middleware, '__name__', type(middleware).__name__).

• Failing test: python/packages/core/tests/core/test_callable_class_middleware_bug.py
• Files examined: python/packages/core/agent_framework/_middleware.py, python/packages/core/pyproject.toml
• Tests run: python/packages/core/tests/core/test_callable_class_middleware_bug.py::TestCallableClassMiddlewareBug::test_determine_middleware_type_raises_attribute_error, python/packages/core/tests/core/test_callable_class_middleware_bug.py::TestCallableClassMiddlewareBug::test_agent_constructor_raises_attribute_error
• Reported version: 1.9.0
• Current version: 1.9.0