Function write_snapshot 

async fn write_snapshot<S>(
    socket: &mut ClientSocket<S>,
    state: &Arc<TransportState>,
    watching: &mut Watching,
    subject: Subject,
    data: Value,
    report: Option<OpenReport>,
) -> Result<()>
where
    S: Sink<Message, Error = Error> + Unpin + Send,

Write a subscribe’s snapshot, register the subject, log the open and spend the showing marks the snapshot completes.

One body for the loop’s reads and the ones served off it: what a client hears and what the trace records must not depend on which side the record was built.