fix: keep __annotations__ in wrap_plugin_route — body params need ForwardRef resolution

Removing __annotations__ broke body parameter resolution: FastAPI could
not resolve ForwardRef('ConversationCreate') etc. causing 422 on all
POST routes with body params. Now keeping annotations from functools.wraps
and only removing return_annotation.

app/core/plugin_error_handler.py

@@ -3,7 +3,7 @@ import logging
 import functools
 import inspect
 from fastapi import UploadFile  # noqa: F401 — needed for ForwardRef resolution
-from fastapi import WebSocket  # noqa: F401 — needed for ForwardRef resolution of WebSocket params
+from fastapi import WebSocket  # noqa: F401 — needed for ForwardRef resolution
 from fastapi.responses import JSONResponse
 
 logger = logging.getLogger(__name__)
@@ -14,7 +14,8 @@ def wrap_plugin_route(handler):
 
     Copies the original handler's signature so FastAPI sees the correct
     parameters (path params, query params, body, etc.) instead of *args/**kwargs.
-    Removes return annotation to prevent ForwardRef('UploadFile') resolution issues.
+    UploadFile and WebSocket are imported in this module's namespace so
+    FastAPI can resolve ForwardRef('UploadFile') and ForwardRef('WebSocket').
     """
     @functools.wraps(handler)
     async def wrapper(*args, **kwargs):
@@ -26,18 +27,16 @@ def wrap_plugin_route(handler):
                 status_code=500,
                 content={'detail': f'Plugin error: {exc}', 'code': 'plugin_error'}
             )
-    # Remove annotations that cause ForwardRef resolution issues
-    wrapper.__annotations__ = {}
     # Remove __wrapped__ so FastAPI doesn't try to resolve the original signature
+    # through the wrapper chain — we set __signature__ explicitly instead.
     if hasattr(wrapper, '__wrapped__'):
         delattr(wrapper, '__wrapped__')
-    # Copy the signature from the original handler but remove return annotation
+    # Copy the signature from the original handler so FastAPI sees correct params.
+    # Keep __annotations__ from functools.wraps (needed for ForwardRef resolution).
+    # Remove only the return annotation to avoid response_model issues.
     try:
         orig_sig = inspect.signature(handler)
-        # Create new signature without return annotation
-        new_params = list(orig_sig.parameters.values())
         wrapper.__signature__ = orig_sig.replace(
-            parameters=new_params,
             return_annotation=inspect.Signature.empty,
         )
     except (ValueError, TypeError):