BaseTask.handoff_to was just deactivate_self + activate_task. Remove
it and add a deactivate_self flag on activate_task instead, so there's
one entry point for activating another task.
LLMTask now overrides activate_task (mirroring its end() override) to
keep the messages / result_callback hooks that finish an in-progress
tool call before the target is activated. All multi-task examples and
unit tests switch to the new call.
Rename ``_build_greeter`` / ``_build_support`` to ``build_greeter`` /
``build_support`` to match the convention used by other multi-task
examples (e.g. ``build_sensor_controller``). They're public factories
the example exposes; the leading underscore was misleading.
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.
Two LLM tasks (greeter and support) handing off to each other over
the local `AsyncQueueBus`. The main task owns the transport
pipeline (STT, TTS, transport I/O) and the child tasks each run
their own LLM behind a `BusBridgeProcessor`. Each child uses
`bridged=()` so `PipelineTask` auto-wraps its pipeline with
the bus edge processors, and `transfer_to_agent` / `end_conversation`
tools demonstrate `handoff_to(...)` and `end(...)`.
