fix: resolve StopIteration by making entire stack synchronous

- Removed async from all MCP tools (create_task, list_tasks, update_task, delete_task, complete_task)
- Made MCP server.call_tool() synchronous
- Made chat endpoint and execute_tool_calls synchronous
- Qwen client already synchronous from previous fix
- All async/await removed from chat flow
- Fixes 'coroutine raised StopIteration' error

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

backend/src/api/chat.py

@@ -4,7 +4,6 @@
 
 import json
 import os
-import asyncio
 from typing import Optional, List, Dict, Any
 from uuid import UUID
 from fastapi import APIRouter, HTTPException, status, Depends
@@ -75,12 +74,12 @@ def extract_tool_call(ai_response: str) -> Optional[Dict[str, Any]]:
     return None
 
 
-async def execute_tool_calls(
+def execute_tool_calls(
     tool_calls: List[Dict[str, Any]],
     mcp_server: MCPServer
 ) -> List[Dict[str, Any]]:
     """
-    Execute multiple tool calls.
+    Execute multiple tool calls (synchronous).
 
     Args:
         tool_calls: List of tool call dicts with 'tool' and 'parameters'
@@ -95,7 +94,7 @@ async def execute_tool_calls(
         parameters = tool_call.get("parameters", {})
 
         try:
-            result = await mcp_server.call_tool(tool_name, parameters)
+            result = mcp_server.call_tool(tool_name, parameters)
             results.append({
                 "tool": tool_name,
                 "success": True,
@@ -113,7 +112,7 @@ async def execute_tool_calls(
 
 
 @router.post("/", response_model=ChatResponse)
-async def chat(
+def chat(
     request: ChatRequest,
     user_id: str = Depends(get_current_user_id),
     session: Session = Depends(get_session)
@@ -200,7 +199,7 @@ async def chat(
         if tool_call:
             # Execute the tool call
             logger.info(f"Executing tool call: {tool_call['tool']}")
-            results = await execute_tool_calls([tool_call], mcp_server)
+            results = execute_tool_calls([tool_call], mcp_server)
             tool_results = results
 
             # Format tool results for AI
@@ -243,6 +242,6 @@ async def chat(
 
 
 @router.get("/health")
-async def health_check():
+def health_check():
     """Health check endpoint for chat API"""
     return {"status": "healthy", "service": "chat-api"}

backend/src/mcp/server.py

@@ -38,15 +38,15 @@ class MCPServer:
 
         Args:
             name: Tool name (e.g., "add_task", "list_tasks")
-            func: Async function implementing the tool
+            func: Synchronous function implementing the tool
             description: Human-readable tool description
         """
         self.tools[name] = func
         logger.info(f"Registered MCP tool: {name} - {description or 'No description'}")
 
-    async def call_tool(self, tool_name: str, parameters: Dict[str, Any]) -> Dict[str, Any]:
+    def call_tool(self, tool_name: str, parameters: Dict[str, Any]) -> Dict[str, Any]:
         """
-        Execute an MCP tool by name.
+        Execute an MCP tool by name (synchronous).
 
         Args:
             tool_name: Name of the tool to execute
@@ -67,7 +67,7 @@ class MCPServer:
         logger.info(f"Executing MCP tool: {tool_name} with parameters: {list(parameters.keys())}")
 
         try:
-            result = await tool_func(**parameters)
+            result = tool_func(**parameters)
             logger.info(f"Tool '{tool_name}' executed successfully")
             return result
         except Exception as e:

backend/src/mcp/tools.py

@@ -18,7 +18,7 @@ class MCPTools:
         self.repo = todo_repository
         self.user_id = user_id
 
-    async def create_task(
+    def create_task(
         self,
         title: str,
         description: Optional[str] = None,
@@ -78,7 +78,7 @@ class MCPTools:
                 "error": f"Failed to create task: {str(e)}"
             }
 
-    async def list_tasks(
+    def list_tasks(
         self,
         status: Optional[str] = None,
         priority: Optional[str] = None,
@@ -129,7 +129,7 @@ class MCPTools:
                 "error": f"Failed to list tasks: {str(e)}"
             }
 
-    async def update_task(
+    def update_task(
         self,
         task_id: str,
         title: Optional[str] = None,
@@ -206,7 +206,7 @@ class MCPTools:
                 "error": f"Failed to update task: {str(e)}"
             }
 
-    async def delete_task(self, task_id: str) -> dict:
+    def delete_task(self, task_id: str) -> dict:
         """
         Delete a task.
 
@@ -244,7 +244,7 @@ class MCPTools:
                 "error": f"Failed to delete task: {str(e)}"
             }
 
-    async def complete_task(self, task_id: str) -> dict:
+    def complete_task(self, task_id: str) -> dict:
         """
         Mark a task as completed.