fix(metrics): stabilize cpu and power sampling

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 {
-		return 0
+	if err == nil {
+		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 {