refactor(link): bound every teardown and handler wait behind one helper [CI]

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

@@ -27,9 +27,6 @@ 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);
-
     /// <summary>一直在发测量报文、却这么久没有收到 Agent 的任何一个：数据面已经不通，重建会话。要比一次线路中断长（中断恢复后接着测），又不能拖到几个小时。</summary>
     private static readonly TimeSpan s_dataIdleLimit = TimeSpan.FromSeconds(90);
     private static readonly RpcRouter<ConnectionSession> s_router = BuildRouter();
@@ -347,18 +344,10 @@ public sealed class AgentConnection : IDisposable
 
     private async Task BoundedAsync(string step, Func<Task> work)
     {
-        try
-        {
-            await work().WaitAsync(s_teardownLimit, _env.Time);
-        }
-        catch (TimeoutException)
+        if (!await Bounded.WaitAsync(work(), Bounded.Teardown, _env.Time))
         {
             _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)