Function answered 

fn answered<T: Serialize + Send + 'static>(
    state: &TransportState,
    command: Command,
    to: u64,
    answer: Receiver<T>,
    reply_tx: &UnboundedSender<Answer>,
)

Dispatch one of those, and answer the client that asked.

A client that asked for an answer always hears one - INCLUDING a refusal, so it is never left watching a channel that stays empty. The wait and the reply are a task’s own, so nothing behind the command waits on them.