feat(update): update the backend like nodes via quadlet restart [CI]

backend/src/MoShiro.Backend/BackendHost.cs

@@ -48,6 +48,7 @@ public static class BackendHost
             services.AddSingleton<IGeoLookup>(new HttpGeoLookup(options.GeoLookupUrl));
         }
 
+        services.AddSingleton<IBackendRestart, HostBackendRestart>();
         services.AddMoShiroApplication(options);
         services.AddMoShiroGateway();
         services.AddMoShiroApi();

backend/src/MoShiro.Backend/HostBackendRestart.cs

@@ -0,0 +1,26 @@
+using Microsoft.Extensions.Hosting;
+using MoShiro.Backend.Application;
+
+namespace MoShiro.Backend;
+
+/// <summary>更新确认之后让 Backend 有序退出：晚一会儿再停，先把确认请求的响应送出去。外面的 Quadlet 单元（<c>Restart=always</c>、<c>Pull=always</c>）会拉最新镜像再启动。</summary>
+public sealed class HostBackendRestart : IBackendRestart
+{
+    private static readonly TimeSpan s_delay = TimeSpan.FromSeconds(1);
+
+    private readonly IHostApplicationLifetime _lifetime;
+    private readonly TimeProvider _time;
+
+    public HostBackendRestart(IHostApplicationLifetime lifetime, TimeProvider time)
+    {
+        _lifetime = lifetime;
+        _time = time;
+    }
+
+    public void Request() =>
+        _ = Task.Run(async () =>
+        {
+            await Task.Delay(s_delay, _time);
+            _lifetime.StopApplication();
+        });
+}