Function wait_for_sign_in 

async fn wait_for_sign_in(
    ctrl_rx: &mut UnboundedReceiver<CtrlMsg>,
    recheck: Duration,
)

Park until a sign-in (ReloadToken) or recheck elapses, whichever comes first. AddAgent/RemoveAgent drain without waking it: they already updated the agents set the next connection subscribes from.