fixing linter

Author: maeste

src/a2a/server/apps/jsonrpc/jsonrpc_app.py

@@ -5,9 +5,9 @@
 
 from abc import ABC, abstractmethod
 from collections.abc import AsyncGenerator, Callable
-from typing import TYPE_CHECKING, Any
+from typing import TYPE_CHECKING, Any, Type, Union
 
-from pydantic import ValidationError
+from pydantic import BaseModel, ValidationError
 
 from a2a.auth.user import UnauthenticatedUser
 from a2a.auth.user import User as A2AUser
@@ -156,7 +156,21 @@ class JSONRPCApplication(ABC):
     """
 
     # Method-to-model mapping for centralized routing
-    METHOD_TO_MODEL = {
+    # Define the union type for all supported request models
+    A2ARequestModel = Union[
+        SendMessageRequest,
+        SendStreamingMessageRequest,
+        GetTaskRequest,
+        CancelTaskRequest,
+        SetTaskPushNotificationConfigRequest,
+        GetTaskPushNotificationConfigRequest,
+        ListTaskPushNotificationConfigRequest,
+        DeleteTaskPushNotificationConfigRequest,
+        TaskResubscriptionRequest,
+        GetAuthenticatedExtendedCardRequest,
+    ]
+    
+    METHOD_TO_MODEL: dict[str, Type[A2ARequestModel]] = {
         'message/send': SendMessageRequest,
         'message/stream': SendStreamingMessageRequest,
         'tasks/get': GetTaskRequest,