pub enum ShutdownBehavior {
    /// The subscriber flushes all pending acks from the application. No further
    /// acks are accepted. The lease loop is closed.
    ///
    /// All other messages under lease management are immediately nacked,
    /// regardless of if they have been returned to the application, or not.
    ///
    /// The shutdown is complete when all pending ack/nack RPCs have completed.
    NackImmediately,

    /// The subscriber will continue to accept acks, for messages it has
    /// delivered to the application. The subscriber will continue to extend
    /// leases for these messages while it waits.
    ///
    /// The subscriber may know about messages that have not been served to the
    /// application yet. These messages are immediately nacked.
    ///
    /// The shutdown is complete when all message handles delivered to the
    /// application have been used, and all pending ack/nack RPCs have
    /// completed.
    WaitForProcessing,
}

pub struct StreamHandle {
  lease_loop: JoinHandle<()>,
}

impl StreamHandle {
  pub async fn shutdown(self, o: ShutdownBehavior);
}

impl StreamHandle {
  pub async fn abandon(self); // NackImmediately
  pub async fn shutdown(self); // WaitForProcessing
}