message: Destroy the BASP broker in the MM destructor
diff: @@ -329,12 +329,18 @@ void middleman::stop() {
  while (backend().try_run_once())
  ; // nop
  }
  - named_brokers_.clear();
  scoped_actor self{system(), true};
  self->send_exit(manager_, exit_reason::kill);
  if (!get_or(config(), "middleman.attach-utility-actors", false))
  self->wait_for(manager_);
  destroy(manager_);
  + // Note: we intentionally don't call `named_brokers_.clear()` here. The BASP
  + // broker must outlive the scheduler threads. The scheduler is stopped
  + // *after* the MM. However, the BASP workers still need to return to their
  + // hub safely, should some of them are still running at this point. By not
  + // clearing the container, we keep the BASP broker (and thus the BASP
  + // instance) alive until the MM module gets destroyed. At that point, all
  + // BASP workers are safe in their hub.
  }
  void middleman::init(actor_system_config& cfg) {
  