fix(channel-monitor): require request samples before health scoring

backend/internal/service/channel_monitor_v2.go

@@ -963,6 +963,9 @@ func ChannelMonitorV2HealthForWithThresholds(metrics ChannelMonitorV2Metric, thr
 		Overall: "unknown", ErrorRate: "unknown", TTFT: "unknown", Cache: "unknown",
 		MinimumSample: thresholds.MinimumSample, Thresholds: thresholds,
 	}
+	if metrics.RequestCount < result.MinimumSample {
+		return result
+	}
 
 	type scored struct {
 		score  float64

backend/internal/service/channel_monitor_v2_test.go

@@ -252,6 +252,81 @@ func TestChannelMonitorV2HealthBlendsErrorTTFTAndCache(t *testing.T) {
 	require.Nil(t, health.Score)
 }
 
+func TestChannelMonitorV2HealthRequiresRequestSamples(t *testing.T) {
+	for _, requestCount := range []int64{0, 8, 9, 49} {
+		t.Run(fmt.Sprintf("requests_%d", requestCount), func(t *testing.T) {
+			thresholds := DefaultChannelMonitorV2HealthThresholds()
+			thresholds.WarningCacheRate = 0.85
+			thresholds.CriticalCacheRate = 0.60
+			metrics := ChannelMonitorV2Metric{SuccessRequests: requestCount, RequestCount: requestCount}
+			if requestCount > 0 {
+				metrics.CacheRateDenominator = 448
+			}
+			health := ChannelMonitorV2HealthForWithThresholds(metrics, thresholds)
+			require.Equal(t, ChannelMonitorV2Health{
+				Overall: "unknown", ErrorRate: "unknown", TTFT: "unknown", Cache: "unknown",
+				MinimumSample: 50, Thresholds: NormalizeChannelMonitorV2HealthThresholds(thresholds),
+			}, health)
+		})
+	}
+}
+
+func TestChannelMonitorV2HealthMinimumSampleBoundaries(t *testing.T) {
+	for _, test := range []struct {
+		name          string
+		minimumSample int64
+		wantMinimum   int64
+	}{
+		{name: "configured", minimumSample: 20, wantMinimum: 20},
+		{name: "configured_one", minimumSample: 1, wantMinimum: 1},
+		{name: "normalized_zero", minimumSample: 0, wantMinimum: 50},
+		{name: "normalized_negative", minimumSample: -1, wantMinimum: 50},
+		{name: "normalized_maximum", minimumSample: 10001, wantMinimum: 10000},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			thresholds := DefaultChannelMonitorV2HealthThresholds()
+			thresholds.MinimumSample = test.minimumSample
+			thresholds.WarningCacheRate = 0.85
+			thresholds.CriticalCacheRate = 0.60
+			p50 := int64(1000)
+			metrics := ChannelMonitorV2Metric{
+				SuccessRequests: test.wantMinimum - 1, RequestCount: test.wantMinimum - 1,
+				CacheRateDenominator: 20000,
+				TTFT:                 ChannelMonitorV2Latency{SampleCount: 20000, P50Ms: &p50},
+			}
+			health := ChannelMonitorV2HealthForWithThresholds(metrics, thresholds)
+			require.Equal(t, ChannelMonitorV2Health{
+				Overall: "unknown", ErrorRate: "unknown", TTFT: "unknown", Cache: "unknown",
+				MinimumSample: test.wantMinimum, Thresholds: NormalizeChannelMonitorV2HealthThresholds(thresholds),
+			}, health)
+
+			metrics.RequestCount = test.wantMinimum
+			metrics.SuccessRequests = test.wantMinimum
+			health = ChannelMonitorV2HealthForWithThresholds(metrics, thresholds)
+			require.Equal(t, test.wantMinimum, health.MinimumSample)
+			require.Equal(t, "healthy", health.ErrorRate)
+			require.Equal(t, "healthy", health.TTFT)
+			require.Equal(t, "critical", health.Cache)
+			require.NotNil(t, health.ErrorRateScore)
+			require.NotNil(t, health.TTFTScore)
+			require.NotNil(t, health.CacheScore)
+			require.NotNil(t, health.Score)
+			require.InDelta(t, 80.0, *health.Score, 0.01)
+			require.Equal(t, "healthy", health.Overall)
+		})
+	}
+}
+
+func TestChannelMonitorV2HealthSufficientHighErrorIsCritical(t *testing.T) {
+	health := ChannelMonitorV2HealthFor(ChannelMonitorV2Metric{
+		RequestCount: 50, ErrorRequests: 50, ErrorRate: 1,
+	})
+	require.Equal(t, "critical", health.ErrorRate)
+	require.Equal(t, "critical", health.Overall)
+	require.NotNil(t, health.Score)
+	require.Zero(t, *health.Score)
+}
+
 func TestChannelMonitorV2HealthLeavesMissingTTFTUnknown(t *testing.T) {
 	health := ChannelMonitorV2HealthFor(ChannelMonitorV2Metric{
 		RequestCount:         200,
@@ -452,6 +527,9 @@ func TestSnapshotRedactsPublicConfigPolicyFields(t *testing.T) {
 			Metrics: ChannelMonitorV2Metric{RequestCount: 100, ErrorRate: 0.1, SuccessRate: 0.9, RPM: 5},
 		},
 	}
+	repo.snap.Health = ChannelMonitorV2HealthFor(repo.snap.Metrics)
+	wantHealth := repo.snap.Health
+	require.NotNil(t, wantHealth.Score)
 	svc := NewChannelMonitorV2Service(repo)
 	snap, err := svc.Snapshot(context.Background(), ChannelMonitorV2Filter{}, false)
 	require.NoError(t, err)
@@ -461,6 +539,7 @@ func TestSnapshotRedactsPublicConfigPolicyFields(t *testing.T) {
 	require.Empty(t, snap.Config.Platforms[0].Models)
 	require.Equal(t, 300, snap.Config.RefreshIntervalSeconds)
 	require.Zero(t, snap.Metrics.RequestCount)
+	require.Equal(t, wantHealth, snap.Health)
 	require.InDelta(t, 0.1, snap.Metrics.ErrorRate, 0.0001)
 	require.Zero(t, snap.Metrics.RPM)
 }