fix(metrics): stabilize cpu and power sampling

audit/internal/platform/live_metrics.go

@@ -68,18 +68,20 @@ func SampleLiveMetrics() LiveMetricSample {
 
 // sampleCPULoadPct reads two /proc/stat snapshots 200ms apart and returns
 // the overall CPU utilisation percentage.
-var cpuStatPrev [2]uint64 // [total, idle]
-
 func sampleCPULoadPct() float64 {
-	total, idle := readCPUStat()
+	total0, idle0 := readCPUStat()
-	if total == 0 {
+	if total0 == 0 {
 		return 0
 	}
-	prevTotal, prevIdle := cpuStatPrev[0], cpuStatPrev[1]
+	time.Sleep(200 * time.Millisecond)
-	cpuStatPrev = [2]uint64{total, idle}
+	total1, idle1 := readCPUStat()
-	if prevTotal == 0 {
+	if total1 == 0 {
 		return 0
 	}
+	return cpuLoadPctBetween(total0, idle0, total1, idle1)
+}
+
+func cpuLoadPctBetween(prevTotal, prevIdle, total, idle uint64) float64 {
 	dt := float64(total - prevTotal)
 	di := float64(idle - prevIdle)
 	if dt <= 0 {

audit/internal/platform/live_metrics_test.go

@@ -42,3 +42,53 @@ func TestCompactAmbientTempName(t *testing.T) {
 		t.Fatalf("got %q", got)
 	}
 }
+
+func TestCPULoadPctBetween(t *testing.T) {
+	tests := []struct {
+		name      string
+		prevTotal uint64
+		prevIdle  uint64
+		total     uint64
+		idle      uint64
+		want      float64
+	}{
+		{
+			name:      "busy half",
+			prevTotal: 100,
+			prevIdle:  40,
+			total:     200,
+			idle:      90,
+			want:      50,
+		},
+		{
+			name:      "fully busy",
+			prevTotal: 100,
+			prevIdle:  40,
+			total:     200,
+			idle:      40,
+			want:      100,
+		},
+		{
+			name:      "no progress",
+			prevTotal: 100,
+			prevIdle:  40,
+			total:     100,
+			idle:      40,
+			want:      0,
+		},
+		{
+			name:      "idle delta larger than total clamps to zero",
+			prevTotal: 100,
+			prevIdle:  40,
+			total:     200,
+			idle:      150,
+			want:      0,
+		},
+	}
+
+	for _, tc := range tests {
+		if got := cpuLoadPctBetween(tc.prevTotal, tc.prevIdle, tc.total, tc.idle); got != tc.want {
+			t.Fatalf("%s: cpuLoadPctBetween(...)=%v want %v", tc.name, got, tc.want)
+		}
+	}
+}

audit/internal/platform/sat_fan_stress.go

@@ -51,6 +51,18 @@ type FanStressRow struct {
 	SysPowerW    float64 // DCMI system power reading
 }
 
+type cachedPowerReading struct {
+	Value     float64
+	UpdatedAt time.Time
+}
+
+var (
+	systemPowerCacheMu sync.Mutex
+	systemPowerCache   cachedPowerReading
+)
+
+const systemPowerHoldTTL = 15 * time.Second
+
 // RunFanStressTest runs a two-phase GPU stress test while monitoring fan speeds,
 // temperatures, and power draw every second. Exports metrics.csv and fan-sensors.csv.
 // Designed to reproduce case-04 fan-speed lag and detect GPU thermal throttling.
@@ -508,11 +520,17 @@ func sampleCPUTempViaSensors() float64 {
 
 // sampleSystemPower reads system power draw via DCMI.
 func sampleSystemPower() float64 {
+	now := time.Now()
+	current := 0.0
 	out, err := exec.Command("ipmitool", "dcmi", "power", "reading").Output()
-	if err != nil {
+	if err == nil {
-		return 0
+		current = parseDCMIPowerReading(string(out))
 	}
-	return parseDCMIPowerReading(string(out))
+	systemPowerCacheMu.Lock()
+	defer systemPowerCacheMu.Unlock()
+	value, updated := effectiveSystemPowerReading(systemPowerCache, current, now)
+	systemPowerCache = updated
+	return value
 }
 
 // parseDCMIPowerReading extracts the instantaneous power reading from ipmitool dcmi output.
@@ -535,6 +553,17 @@ func parseDCMIPowerReading(raw string) float64 {
 	return 0
 }
 
+func effectiveSystemPowerReading(cache cachedPowerReading, current float64, now time.Time) (float64, cachedPowerReading) {
+	if current > 0 {
+		cache = cachedPowerReading{Value: current, UpdatedAt: now}
+		return current, cache
+	}
+	if cache.Value > 0 && !cache.UpdatedAt.IsZero() && now.Sub(cache.UpdatedAt) <= systemPowerHoldTTL {
+		return cache.Value, cache
+	}
+	return 0, cache
+}
+
 // analyzeThrottling returns true if any GPU reported an active throttle reason
 // during either load phase.
 func analyzeThrottling(rows []FanStressRow) bool {

audit/internal/platform/sat_fan_stress_test.go

@@ -1,6 +1,9 @@
 package platform
 
-import "testing"
+import (
+	"testing"
+	"time"
+)
 
 func TestParseFanSpeeds(t *testing.T) {
 	raw := "FAN1 | 2400.000 | RPM | ok\nFAN2 | 1800 RPM | ok | ok\nFAN3 | na | RPM | ns\n"
@@ -25,3 +28,40 @@ func TestFirstFanInputValue(t *testing.T) {
 		t.Fatalf("got=%v ok=%v", got, ok)
 	}
 }
+
+func TestParseDCMIPowerReading(t *testing.T) {
+	raw := `
+Instantaneous power reading:                   512 Watts
+Minimum during sampling period:               498 Watts
+`
+	if got := parseDCMIPowerReading(raw); got != 512 {
+		t.Fatalf("parseDCMIPowerReading()=%v want 512", got)
+	}
+}
+
+func TestEffectiveSystemPowerReading(t *testing.T) {
+	now := time.Now()
+	cache := cachedPowerReading{Value: 480, UpdatedAt: now.Add(-5 * time.Second)}
+
+	got, updated := effectiveSystemPowerReading(cache, 0, now)
+	if got != 480 {
+		t.Fatalf("got=%v want cached 480", got)
+	}
+	if updated.Value != 480 {
+		t.Fatalf("updated=%+v", updated)
+	}
+
+	got, updated = effectiveSystemPowerReading(cache, 530, now)
+	if got != 530 {
+		t.Fatalf("got=%v want 530", got)
+	}
+	if updated.Value != 530 {
+		t.Fatalf("updated=%+v", updated)
+	}
+
+	expired := cachedPowerReading{Value: 480, UpdatedAt: now.Add(-systemPowerHoldTTL - time.Second)}
+	got, _ = effectiveSystemPowerReading(expired, 0, now)
+	if got != 0 {
+		t.Fatalf("expired cache returned %v want 0", got)
+	}
+}

audit/internal/webui/server_test.go

@@ -89,6 +89,19 @@ func TestChartDataFromSamplesUsesFullHistory(t *testing.T) {
 	}
 }
 
+func TestNormalizePowerSeriesHoldsLastPositive(t *testing.T) {
+	got := normalizePowerSeries([]float64{0, 480, 0, 0, 510, 0})
+	want := []float64{0, 480, 480, 480, 510, 510}
+	if len(got) != len(want) {
+		t.Fatalf("len=%d want %d", len(got), len(want))
+	}
+	for i := range want {
+		if got[i] != want[i] {
+			t.Fatalf("got[%d]=%v want %v", i, got[i], want[i])
+		}
+	}
+}
+
 func TestRootRendersDashboard(t *testing.T) {
 	dir := t.TempDir()
 	path := filepath.Join(dir, "audit.json")