message: Comment Runner::poll_next
diff: @@ -51,6 +51,9 @@ where
  Poll::Pending => true,
  };
  loop {
  + // Try to take take a new message that isn't already being processed
  + // leave the already-processing ones in the queue, so that we can take them once
  + // we're free again.
  let next_msg_poll = scheduler
  .as_mut()
  .hold_unless(|msg| !slots.contains_key(msg))
  