add typecheck

Author: gyang-xai

src/mcp/client/streamable_http.py

@@ -254,9 +254,10 @@ async def _handle_resumption_request(self, ctx: RequestContext) -> None:
     async def _send_error_response(self, ctx: RequestContext, error: Exception) -> None:
         """Send an error response to the client."""
         error_data = ErrorData(code=32000, message=str(error))
-        jsonrpc_error = JSONRPCError(jsonrpc="2.0", id=ctx.session_message.message.root.id, error=error_data)
-        session_message = SessionMessage(message=JSONRPCMessage(jsonrpc_error))
-        await ctx.read_stream_writer.send(session_message)
+        if isinstance(ctx.session_message.message.root, JSONRPCRequest):
+            jsonrpc_error = JSONRPCError(jsonrpc="2.0", id=ctx.session_message.message.root.id, error=error_data)
+            session_message = SessionMessage(message=JSONRPCMessage(jsonrpc_error))
+            await ctx.read_stream_writer.send(session_message)
 
     async def _handle_post_request(self, ctx: RequestContext) -> None:
         """Handle a POST request with response processing."""