Function run 

pub async fn run<S>(
    listener: Listener,
    daemon: Arc<Daemon>,
    shutdown: S,
) -> Result<Stopped>
where
    S: Future<Output = ()> + Send,

Accept until shutdown resolves, then stop accepting, drain, and checkpoint.

The order is the contract’s: acceptance stops FIRST, so no connection starts during the drain, then in-flight work gets at most DRAIN_TIMEOUT_SECS, then the projections are snapshotted at the watermark — after the drain, so the snapshot includes the last append rather than racing it — and only then is the socket removed, and only if it is still the file this process created.