fix(probe): bound every step of tearing down an Agent session [CI]

backend/probe/src/MoShiro.Probe/Link/AgentConnection.cs

@@ -26,6 +26,9 @@ public sealed class AgentConnection : IDisposable
 
     /// <summary>Agent 的任何帧（时钟回复、任务集）都算存活；比时钟同步间隔长得多，容得下差线路上的黑洞，但不会让一个 Agent 已经丢掉的会话永远挂着。</summary>
     private static readonly TimeSpan s_idleLimit = TimeSpan.FromSeconds(120);
+
+    /// <summary>收尾的每一步最多等这么久：QUIC 连接或控制连接的关闭卡在原生层时，不能让整个重拨循环跟着卡住。</summary>
+    private static readonly TimeSpan s_teardownLimit = TimeSpan.FromSeconds(5);
     private static readonly RpcRouter<ConnectionSession> s_router = BuildRouter();
 
     /// <summary>对等面入站方法的路由器（只读，测试用）。</summary>
@@ -209,7 +212,7 @@ public sealed class AgentConnection : IDisposable
         var remote = (IPEndPoint)info.Remote!;
         IReadOnlyList<int> quicPorts = Endpoint.EffectiveQuicPorts;
         int quicPort = quicPorts.Count == 0 ? 7443 : quicPorts[0];
-        await using var datagrams = new QuicDatagramTransport(
+        var datagrams = new QuicDatagramTransport(
             data,
             _env.Clock,
             new DataPlaneCounters(),
@@ -308,7 +311,7 @@ public sealed class AgentConnection : IDisposable
             }
 
             await cts.CancelAsync();
-            await Task.WhenAll(Quiet(run), Quiet(receive), Quiet(pump), Quiet(maintenance));
+            await BoundedAsync("stop tasks", () => Task.WhenAll(Quiet(run), Quiet(receive), Quiet(pump), Quiet(maintenance)));
             return reason;
         }
         finally
@@ -316,11 +319,12 @@ public sealed class AgentConnection : IDisposable
             _session = null;
             Volatile.Write(ref _activeDatagrams, null);
             await cts.CancelAsync();
-            await session.StopAllAsync();
-            await Quiet(run);
-            await Quiet(receive);
-            await Quiet(pump);
-            await rpc.DisposeAsync();
+            await BoundedAsync("stop blocks", session.StopAllAsync);
+            await BoundedAsync("wait control", () => Quiet(run));
+            await BoundedAsync("wait datagrams", () => Quiet(receive));
+            await BoundedAsync("wait pump", () => Quiet(pump));
+            await BoundedAsync("dispose control", () => rpc.DisposeAsync().AsTask());
+            await BoundedAsync("dispose quic", () => datagrams.DisposeAsync().AsTask());
         }
     }
 
@@ -338,6 +342,22 @@ public sealed class AgentConnection : IDisposable
         }
     }
 
+    private async Task BoundedAsync(string step, Func<Task> work)
+    {
+        try
+        {
+            await work().WaitAsync(s_teardownLimit, _env.Time);
+        }
+        catch (TimeoutException)
+        {
+            _env.Log.Warn("agent session teardown step timed out, moving on", ("agent", Endpoint.AgentId), ("step", step));
+        }
+        catch (Exception ex) when (ex is OperationCanceledException or IOException or ObjectDisposedException or System.Net.Sockets.SocketException or InvalidOperationException)
+        {
+            // 会话结束时的正常噪声
+        }
+    }
+
     private static async Task Quiet(Task task)
     {
         try