Function serve 

pub async fn serve(
    server: BoundServer,
    shutdown: impl Future<Output = ()> + Send + 'static,
) -> Result<()>

Serves server until shutdown resolves, then drains in-flight HTTP connections and cancels/waits for any still-active tune run before returning – the interactive path’s main.rs awaits shutdown_signal; the Windows service path (crate::service::windows_impl) awaits its own SCM-driven signal instead.