Function attach_terminal 

async fn attach_terminal<S>(
    socket: &mut ClientSocket<S>,
    state: &Arc<TransportState>,
    terminal: &mut TerminalViewingState,
    me: u64,
    seat: SessionSlot,
    id: Option<u16>,
    cols: Option<u16>,
    rows: Option<u16>,
    reply_to: Option<u64>,
) -> Result<()>
where
    S: Sink<Message, Error = Error> + Unpin + Send,

Attach this connection to a seat’s terminal as a viewer.

The answer is the screen as a VT stream, so a page that opens a terminal nobody has drawn yet has content immediately; frames follow.