fix: prevent QUIC heartbeat stalls and isolate TCP retransmission counters [CI] [SKIP TESTS]

backend/shared/MoShiro.Measurement/Net/TcpInfo.cs

@@ -70,14 +70,15 @@ public static class TcpInfo
 }
 
 /// <summary>
-/// 一条连接上周期性的内核采样（<c>tcp_info</c> 流）：每个采样一行 (ts, side, srtt, rttvar, cwnd, retrans_total, segs_out, bytes_acked)。
+/// 一条连接上周期性的内核采样（<c>tcp_info</c> 流）：每个采样一行 (ts, side, srtt, rttvar, cwnd, retrans_total, segs_out, bytes_acked, conn)。
 /// 两端各采样自己的套接字：Probe 的重传反映上行方向，Agent 的重传反映下行方向（代理场景里大流量走这个方向）。
-/// 累计计数器在 Backend 按 side 分别求差。
+/// 累计计数器在 Backend 按 (side, conn) 分别求差；conn 是当前记录器内分配的连接编号，不包含网络地址。
 /// </summary>
 public sealed class TcpInfoRecorder
 {
     private readonly MonoClock _clock;
     private readonly long _side;
+    private long _nextConnection;
 
     public TcpInfoRecorder(StreamSpec spec, Side side, MonoClock clock)
     {
@@ -96,6 +97,9 @@ public sealed class TcpInfoRecorder
             return;
         }
 
+        // A recorder survives reconnects, and listeners can briefly have more
+        // than one socket. Kernel counters belong to a socket, not just a side.
+        long connection = Interlocked.Increment(ref _nextConnection);
         try
         {
             using var timer = new PeriodicTimer(interval, _clock.Time);
@@ -107,7 +111,7 @@ public sealed class TcpInfoRecorder
                 }
 
                 long key = Rows.Append();
-                Rows.SetRow(key, [_clock.NowUs(), _side, s.SrttUs, s.RttVarUs, s.Cwnd, s.TotalRetrans, s.SegsOut, s.BytesAcked]);
+                Rows.SetRow(key, [_clock.NowUs(), _side, s.SrttUs, s.RttVarUs, s.Cwnd, s.TotalRetrans, s.SegsOut, s.BytesAcked, connection]);
             }
         }
         catch (OperationCanceledException)