- Replace on_worker_connected() post-hoc call with WorkerConnectedCallback
that fires inside CallAdapter::handle(). handle() blocks until disconnect
— there is no 'after handle accepts' point for the assembly layer to
hook into. The callback carries both on_connected (from_call + attach_peer)
and on_disconnected (detach_peer + drop channels).
- Add CallAdapter::with_worker_connected_callback(callback) builder method.
- Consolidate duplicate WorkerConnectedCallback struct definitions.
- Fix channel role: 'channel proxying' → 'channel management'. The hub
tracks channels; it does not proxy streams. What the caller does with
the resulting channel is the assembly layer's business.
- Resolve OQ-54: callback is the committed design. Update OQ file and
open-questions.md table.