How does the Generic Host manage the application's startup and shutdown lifecycle, including handling OS signals like SIGTERM?

The host registers signal handlers (via IHostApplicationLifetime and platform-specific mechanisms) for graceful shutdown signals -- SIGTERM/SIGINT on Linux/macOS, Ctrl+C or service stop on Windows -- triggering ApplicationStopping, then calling StopAsync on all registered IHostedService instances (respecting the configured ShutdownTimeout grace period) before ApplicationStopped fires, ensuring resources are cleaned up and in-flight work has a chance to complete before the process actually terminates, which is especially important in container orchestrators that send SIGTERM before forcibly killing a container.

public class MyService(IHostApplicationLifetime lifetime) : IHostedService {
    public Task StartAsync(CancellationToken ct) {
        lifetime.ApplicationStarted.Register(() => Console.WriteLine("Started"));
        lifetime.ApplicationStopping.Register(() => Console.WriteLine("Stopping..."));
        return Task.CompletedTask;
    }
    public Task StopAsync(CancellationToken ct) => Task.CompletedTask;
}