feat(quic): replace probe UDP data plane with QUIC datagrams

backend/src/MoShiro.Backend.Analysis/Ops/EchoOps.cs

@@ -273,7 +273,14 @@ internal static class JitterEmitter
 /// <summary>连续丢失段的长度（按发送顺序）。</summary>
 internal sealed class LossRunsOp : MetricOp
 {
-    public override string Signature => "loss_runs/1";
+    private readonly Dir _direction;
+
+    public LossRunsOp(Dir direction)
+    {
+        _direction = direction;
+    }
+
+    public override string Signature => $"loss_runs/{_direction}/2";
 
     public override void Evaluate(ChunkView view, RawStream stream, IObservationSink sink)
     {
@@ -292,7 +299,13 @@ internal sealed class LossRunsOp : MetricOp
                 continue;
             }
 
-            if (c.IsReplyLost(i))
+            bool lost = _direction switch
+            {
+                Dir.Up => c.IsUpLost(i),
+                Dir.Down => !c.IsUpLost(i) && c.IsReplyLost(i),
+                _ => c.IsReplyLost(i),
+            };
+            if (lost)
             {
                 if (run == 0)
                 {
@@ -315,6 +328,59 @@ internal sealed class LossRunsOp : MetricOp
     }
 }
 
+/// <summary>每个块一个最长连续丢包值；无丢包的有效块明确输出 0。</summary>
+internal sealed class LossRunMaxOp(Dir direction) : MetricOp
+{
+    public override string Signature => $"loss_run_max/{direction}/1";
+
+    public override void Evaluate(ChunkView view, RawStream stream, IObservationSink sink)
+    {
+        var c = new EchoColumns(stream);
+        if (!c.HasBasics || (direction != Dir.Total && c.T2 is null))
+        {
+            return;
+        }
+
+        int run = 0;
+        int maximum = 0;
+        bool hasSample = false;
+        long sampleAt = 0;
+        for (int i = 0; i < c.Count; i++)
+        {
+            if (!c.T1!.IsValid(i))
+            {
+                continue;
+            }
+
+            bool lost = direction switch
+            {
+                Dir.Up => c.IsUpLost(i),
+                Dir.Down => !c.IsUpLost(i) && c.IsReplyLost(i),
+                _ => c.IsReplyLost(i),
+            };
+            if (direction == Dir.Down && c.IsUpLost(i))
+            {
+                // A request lost before reaching the Agent is not a downstream sample.
+                run = 0;
+                continue;
+            }
+
+            if (!hasSample)
+            {
+                sampleAt = c.SentUtcMs(view, i);
+                hasSample = true;
+            }
+            run = lost ? run + 1 : 0;
+            maximum = Math.Max(maximum, run);
+        }
+
+        if (hasSample)
+        {
+            sink.Emit(sampleAt, maximum);
+        }
+    }
+}
+
 /// <summary>乱序：按到达顺序，序号比之前见过的最大序号还小。重复的序号不算乱序。</summary>
 internal sealed class ReorderOp : MetricOp
 {