refactor: harden diagnostics and consolidate runtime code

audit/internal/platform/sat_fan_stress.go

@@ -571,21 +571,6 @@ func sampleFanSpeedsViaSensorsJSON() ([]FanReading, error) {
 	return fans, nil
 }
 
-// sampleFanDutyCyclePct reads fan PWM/duty-cycle controls from lm-sensors.
-// Returns the average duty cycle across all exposed PWM controls.
-func sampleFanDutyCyclePct() (float64, bool, bool) {
-	out, err := exec.Command("sensors", "-j").Output()
-	if err != nil || len(out) == 0 {
-		fans, fanErr := sampleFanSpeeds()
-		if fanErr != nil {
-			return 0, false, false
-		}
-		return sampleFanDutyCyclePctFromFans(fans)
-	}
-	pct, ok := parseFanDutyCyclePctSensorsJSON(out)
-	return pct, ok, false
-}
-
 func sampleFanDutyCyclePctFromFans(fans []FanReading) (float64, bool, bool) {
 	if len(fans) == 0 {
 		return 0, false, false
@@ -682,27 +667,7 @@ func normalizePWMAsDutyPct(raw float64) (float64, bool) {
 }
 
 func firstFanInputValue(feature map[string]any) (float64, bool) {
-	keys := make([]string, 0, len(feature))
-	for key := range feature {
-		keys = append(keys, key)
-	}
-	sort.Strings(keys)
-	for _, key := range keys {
-		lower := strings.ToLower(key)
-		if !strings.Contains(lower, "fan") || !strings.HasSuffix(lower, "_input") {
-			continue
-		}
-		switch value := feature[key].(type) {
-		case float64:
-			return value, true
-		case string:
-			f, err := strconv.ParseFloat(value, 64)
-			if err == nil {
-				return f, true
-			}
-		}
-	}
-	return 0, false
+	return firstSensorInputValue(feature, "fan")
 }
 
 // sampleCPUMaxTemp returns the highest CPU/inlet temperature from ipmitool or sensors.