Whenever the self-handle is removed for a reason other than RENAMED, Tp::Channel should remember the reason and other details (in particular, the actor and any D-Bus error name).

If the channel closes thereafter, the reason and other details should be used to construct a more suitable error name than Cancelled. (For instance, if there is a D-Bus error name, use that; if not, and the reason is None, use Cancelled if the actor is the self handle or Terminated otherwise; and so on.)

telepathy-glib has similar logic which can be used as a reference.