I think @rkuhn is talking about the more general case where the reference is used after the await. In that case, accessing the object without it being Sync is unsound in general. But if we could somehow prove that the object in question uniquely belongs to this async 'thread' (task, chain of futures, whatever you want to call it) – in other words, that if the current async fn is sent to another thread, all other code accessing the object will also be sent to that same thread – then it would be sound.
2 Likes