fix: make ContextInjector async to match ToolCallInterceptor protocol

The interceptor __call__ method must be async and follow the proper
signature: async __call__(request, handler) -> result

Previous implementation was synchronous and had wrong signature, causing
'object function can't be used in await expression' error.

agent/context_injector.py

@@ -5,7 +5,7 @@ This interceptor automatically injects `signature` and `today_date` parameters
 into buy/sell tool calls to support concurrent multi-model simulations.
 """
 
-from typing import Any, Dict
+from typing import Any, Callable, Awaitable
 
 
 class ContextInjector:
@@ -28,23 +28,28 @@ class ContextInjector:
         self.signature = signature
         self.today_date = today_date
 
-    def __call__(self, tool_name: str, tool_input: Dict[str, Any]) -> Dict[str, Any]:
+    async def __call__(
+        self,
+        request: Any,  # MCPToolCallRequest
+        handler: Callable[[Any], Awaitable[Any]]
+    ) -> Any:  # MCPToolCallResult
         """
         Intercept tool call and inject context parameters.
 
         Args:
-            tool_name: Name of the tool being called
-            tool_input: Original tool input parameters
+            request: Tool call request containing name and arguments
+            handler: Async callable to execute the actual tool
 
         Returns:
-            Modified tool input with injected context
+            Result from handler after injecting context
         """
-        # Only inject for trade tools (buy/sell)
-        if tool_name in ["buy", "sell"]:
-            # Inject signature and today_date if not already provided
-            if "signature" not in tool_input:
-                tool_input["signature"] = self.signature
-            if "today_date" not in tool_input:
-                tool_input["today_date"] = self.today_date
+        # Inject signature and today_date for trade tools
+        if request.name in ["buy", "sell"]:
+            # Add signature and today_date to arguments if not present
+            if "signature" not in request.arguments:
+                request.arguments["signature"] = self.signature
+            if "today_date" not in request.arguments:
+                request.arguments["today_date"] = self.today_date
 
-        return tool_input
+        # Call the actual tool handler
+        return await handler(request)