Switch every example to ``await runner.spawn(task)`` followed by
``await runner.run()`` (no task argument), and ``await runner.cancel()``
on client-disconnected instead of ``await task.cancel()``. This makes
the main pipeline task look the same as the worker / proxy tasks
spawned alongside it, and lets ``runner.cancel()`` drive a uniform
shutdown across every root task on the bus.
A voice moderator that fans out a debate topic to three worker
tasks (advocate, critic, analyst) via `task.job_group(...)`,
then synthesizes their replies. Workers are `LLMContextTask`s
that keep their own conversation context across rounds and use
the assistant-aggregator's `on_assistant_turn_stopped` event
to ship the completed turn back as a job response.
