Wrap JSONRPC messages with SessionMessage for metadata support (#590)

tests/server/test_session.py

@@ -7,11 +7,11 @@ from mcp.server import Server
 from mcp.server.lowlevel import NotificationOptions
 from mcp.server.models import InitializationOptions
 from mcp.server.session import ServerSession
+from mcp.shared.message import SessionMessage
 from mcp.shared.session import RequestResponder
 from mcp.types import (
     ClientNotification,
     InitializedNotification,
-    JSONRPCMessage,
     PromptsCapability,
     ResourcesCapability,
     ServerCapabilities,
@@ -21,10 +21,10 @@ from mcp.types import (
 @pytest.mark.anyio
 async def test_server_session_initialize():
     server_to_client_send, server_to_client_receive = anyio.create_memory_object_stream[
-        JSONRPCMessage
+        SessionMessage
     ](1)
     client_to_server_send, client_to_server_receive = anyio.create_memory_object_stream[
-        JSONRPCMessage
+        SessionMessage
     ](1)
 
     # Create a message handler to catch exceptions