Function spawn_completing 

pub fn spawn_completing<T, E>(
    operation: &'static str,
    bugs: Arc<dyn BugSink>,
    work: impl Future<Output = Result<T, E>> + Send + 'static,
) -> CompletingTask<Result<T, E>> 
where
    T: Send + 'static,
    E: CarriesBug + Send + 'static,

Run work, named operation, as its own task, so it finishes even when its caller stops waiting, as closing a store does. Its panic comes back as TaskFailed::Panicked to a caller still waiting. Once none is, the panic goes to bugs, as does a bug its error carries.