This is a bit strange.  I understand that the dashboard.on_error= call is necessary here, since this is a dashboard-specific thing, but the participant registration is storage-specific.  Not sure what the right answer is, here, and for now this works fine, since in the normal case it just means the participant will be registered twice, which doesn't actually add it twice to the list.  But maybe we should talk about what it would mean to attempt to run start_worker! without having called register_participants first.  Should that even be allowed?