error.Error.ObjectGone

This is distinct from a connection failure: tmux answered, and the object was not among the results. It has been closed or killed since the handle was created.

For a client, absence from a listing has one other cause that is not this: a stopped client is left out of the same listing and comes back. That is Self::ClientSuspended , reported separately so that Self::is_object_gone keeps meaning "stop using this handle".