Function serve_with_dashboard 

pub async fn serve_with_dashboard(
    app: Arc<App>,
    addr: SocketAddr,
    shutdown: Receiver<bool>,
    dashboard: Option<Arc<Dashboard>>,
) -> Result<()>

Serve, optionally with the dashboard mounted under /_beck.

Optional because the dashboard needs the infrastructure graph, which beck-rt cannot build — it does not depend on beck-infra, and should not: the runtime does not know what Kubernetes is. Whoever assembles the process knows both, and passes one in.