agent: unify listening and dialing with directed mutual measurements

Replace Probe with Agent across node runtime, Fleet contracts, backend state, API and storage. Report incoming sessions and outgoing link health through each Agent uplink, and retain directed link controls and retry.

Update protocol fixtures and end-to-end coverage for the unified model; accept requested cancellation during the Fleet timeout test cleanup.

backend/shared/MoShiro.Measurement/Blocks/Train.cs

@@ -7,7 +7,7 @@ namespace MoShiro.Measurement;
 
 /// <summary>
 /// 单向数据流（UDP train），监听方（Agent，行的主导方）：按声明的码率均匀发包，发出的每个包 (seq, size, t_send) 记在按序号的记录里，
-/// Probe 的接收时刻之后按序号合并（没有到达的就是丢失）。发送在专用线程上完成，不占用线程池。
+/// 拨号方 的接收时刻之后按序号合并（没有到达的就是丢失）。发送在专用线程上完成，不占用线程池。
 /// 等不到对端的地址（5 秒内没有任何认证过的包）就以 <see cref="BlockFaultException"/> 结束。
 /// </summary>
 public sealed class TrainListener : BlockBase
@@ -21,7 +21,7 @@ public sealed class TrainListener : BlockBase
         : base(env, spec)
     {
         double pps = spec.Params.GetNumber("mbps") * 1_000_000 / 8 / Math.Max(1, spec.Int("size"));
-        _records = new RowStore(spec.Kind.FindStream("pkt")!, Side.Agent, (int)Math.Clamp(pps * spec.Int("duration_s") * 1.25, 1024, 4_000_000));
+        _records = new RowStore(spec.Kind.FindStream("pkt")!, Side.Listener, (int)Math.Clamp(pps * spec.Int("duration_s") * 1.25, 1024, 4_000_000));
     }
 
     public override long Produced => Interlocked.Read(ref _sent);
@@ -30,7 +30,7 @@ public sealed class TrainListener : BlockBase
 
     public override async Task RunAsync(CancellationToken ct)
     {
-        // Probe 开始前发来的探活包（Data）要被接受，准入策略才能据此学到它当前的源地址（NAT 映射）；它们本身没有内容
+        // 拨号方 开始前发来的探活包（Data）要被接受，准入策略才能据此学到它当前的源地址（NAT 映射）；它们本身没有内容
         Env.Datagrams!.Register(Spec.StreamId, static (in QuicDatagramDelivery _) => { });
         try
         {
@@ -138,7 +138,7 @@ public sealed class TrainListener : BlockBase
 }
 
 /// <summary>
-/// 单向数据流，拨号方（Probe，行的跟随方）：接收，记录每个序号第一次到达的时刻（按序号索引，热路径不分配）；
+/// 单向数据流，拨号方（行的跟随方）：接收，记录每个序号第一次到达的时刻（按序号索引，热路径不分配）；
 /// 序号超过本地包速率上限推算出的范围时忽略。阶段结束时按序号范围切成多个列块交给 Agent，每块不超过 <see cref="ProtocolLimits.MaxRecordsPerChunk"/> 的记录。
 /// 开始时先发几个探活包，让 Agent 学到我们当前的源地址（NAT 映射）再开始发送。
 /// </summary>
@@ -159,9 +159,9 @@ public sealed class TrainDialer : BlockBase
         double pps = spec.Params.GetNumber("mbps") * 1_000_000 / 8 / Math.Max(1, spec.Int("size"));
         long seconds = Math.Max(1, spec.Int("duration_s"));
         _maxSeq = Math.Max(1024, Math.Min((long)(pps * seconds * 1.25), env.MaxPacketsPerSecond * seconds * 3 / 2));
-        _received = new RowStore(spec.Kind.FindStream("pkt")!, Side.Probe, (int)_maxSeq);
+        _received = new RowStore(spec.Kind.FindStream("pkt")!, Side.Dialer, (int)_maxSeq);
         _tRecv = _received.ColumnIndex("t_recv");
-        _step = new RowStore(spec.Kind.FindStream("step")!, Side.Probe, 16);
+        _step = new RowStore(spec.Kind.FindStream("step")!, Side.Dialer, 16);
     }
 
     public override async Task RunAsync(CancellationToken ct)