/// Cross-platform shutdown signal handling.
///
/// Provides a unified async future that resolves when the process should
/// shut down (SIGINT/SIGTERM on Unix, Ctrl+C/Ctrl+Break on Windows).
pub async fn shutdown_signal() {
    #[cfg(unix)]
    {
        use tokio::signal::unix::{SignalKind, signal};
        let mut sigint =
            signal(SignalKind::interrupt()).expect("failed to create SIGINT signal handler");
        let mut sigterm =
            signal(SignalKind::terminate()).expect("failed to create SIGTERM signal handler");
        tokio::select! {
            _ = sigint.recv() => {},
            _ = sigterm.recv() => {},
        }
    }
    #[cfg(not(unix))]
    {
        tokio::signal::ctrl_c().await.ok();
    }
}