fix(client): eliminate resolver probation starvation in LossThenLatency balancing strategy

internal/client/balancer.go

@@ -1805,7 +1805,7 @@ func (b *Balancer) hasLossSignalLocked() bool {
 			continue
 		}
 		sent, _, _, _, _ := stats.snapshot()
-		if sent >= 5 {
+		if sent > 0 {
 			return true
 		}
 	}
@@ -1819,7 +1819,7 @@ func (b *Balancer) hasLatencySignalLocked() bool {
 			continue
 		}
 		_, _, _, _, count := stats.snapshot()
-		if count >= 5 {
+		if count > 0 {
 			return true
 		}
 	}
@@ -2032,13 +2032,10 @@ func (b *Balancer) leastLossTopTierCandidatesLocked(excludeKey string) []Connect
 
 func (b *Balancer) lossScoreLocked(idx int) uint64 {
 	if idx < 0 || idx >= len(b.stats) || b.stats[idx] == nil {
-		return 200 // Use a more neutral default for unknown
+		return 0
 	}
 	sent, _, lost, _, _ := b.stats[idx].snapshot()
-	if sent < 5 {
-		return 200 // Initial probation
-	}
-	if lost == 0 {
+	if sent == 0 || lost == 0 {
 		return 0
 	}
 	return (lost * 1000) / sent
@@ -2049,7 +2046,7 @@ func (b *Balancer) latencyScoreLocked(idx int) uint64 {
 		return 999000
 	}
 	_, _, _, sum, count := b.stats[idx].snapshot()
-	if count < 5 {
+	if count == 0 {
 		return 999000
 	}
 	return sum / count

internal/client/balancer_test.go

@@ -462,3 +462,34 @@ func TestBalancerSetConnectionMTUUpdatesBalancerOnly(t *testing.T) {
 		t.Fatalf("expected snapshot MTUs to update, got up=%d chars=%d down=%d", got.UploadMTUBytes, got.UploadMTUChars, got.DownloadMTUBytes)
 	}
 }
+
+func TestBalancerLossThenLatency_NoProbationStarvation(t *testing.T) {
+	b := NewBalancer(BalancingLossThenLatency, nil)
+	connections := []*Connection{
+		{Key: "slow-established", IsValid: true},
+		{Key: "fast-new", IsValid: true},
+	}
+	b.SetConnections(connections)
+	_ = b.SetConnectionValidity("slow-established", true)
+	_ = b.SetConnectionValidity("fast-new", true)
+
+	// "slow-established" has 10 packets, 0 loss, 600ms latency
+	for i := 0; i < 10; i++ {
+		b.ReportSend("slow-established")
+		b.ReportSuccess("slow-established", 600*time.Millisecond)
+	}
+
+	// "fast-new" has 2 packets, 0 loss, 45ms latency (previously trapped under sent < 5 probation)
+	for i := 0; i < 2; i++ {
+		b.ReportSend("fast-new")
+		b.ReportSuccess("fast-new", 45*time.Millisecond)
+	}
+
+	best, ok := b.GetBestConnection()
+	if !ok {
+		t.Fatal("expected a valid connection")
+	}
+	if best.Key != "fast-new" {
+		t.Fatalf("expected fast newly reactivated resolver to be picked, got %q", best.Key)
+	}
+}