[Demo]: Task List is empty, and message is pending

When I try this demo you provided, it doesn't work.
frontend:

backend:

The issue reports a demo not working with screenshots showing empty task lists and pending messages. Start by running the demo to reproduce the issue, checking the backend logs for errors, and comparing the setup against the documented steps. Determine if the problem is in the sample code, configuration, or the underlying A2A protocol implementation.

Written by the indexing model from the issue text.