feat(audit): fan-stress SAT for MSI case-04 fan lag & thermal throttle detection

Two-phase GPU thermal cycling test with per-second telemetry:
- Phases: baseline → load1 → pause (no cooldown) → load2 → cooldown
- Monitors: fan RPM (ipmitool sdr), CPU/server temps (ipmitool/sensors),
  system power (ipmitool dcmi), GPU temp/power/usage/clock/throttle (nvidia-smi)
- Detects throttling via clocks_throttle_reasons.active bitmask
- Measures fan response lag from load start (validates case-04 ~2s lag)
- Exports metrics.csv (wide format, one row/sec) and fan-sensors.csv (long format)
- TUI: adds [F] Fan Stress Test to Health Check screen with Quick/Standard/Express modes

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

audit/internal/app/app.go

@@ -80,6 +80,7 @@ type satRunner interface {
 	DetectGPUVendor() string
 	ListAMDGPUs() ([]platform.AMDGPUInfo, error)
 	RunAMDAcceptancePack(baseDir string) (string, error)
+	RunFanStressTest(ctx context.Context, baseDir string, opts platform.FanStressOptions) (string, error)
 }
 
 type runtimeChecker interface {
@@ -491,6 +492,67 @@ func (a *App) RunAMDAcceptancePackResult(baseDir string) (ActionResult, error) {
 	return ActionResult{Title: "AMD GPU SAT", Body: satResultBody(path)}, err
 }
 
+func (a *App) RunFanStressTest(ctx context.Context, baseDir string, opts platform.FanStressOptions) (string, error) {
+	if strings.TrimSpace(baseDir) == "" {
+		baseDir = DefaultSATBaseDir
+	}
+	return a.sat.RunFanStressTest(ctx, baseDir, opts)
+}
+
+func (a *App) RunFanStressTestResult(ctx context.Context, opts platform.FanStressOptions) (ActionResult, error) {
+	path, err := a.RunFanStressTest(ctx, "", opts)
+	body := formatFanStressResult(path)
+	if err != nil && err != context.Canceled {
+		body += "\nERROR: " + err.Error()
+	}
+	return ActionResult{Title: "Fan Stress Test", Body: body}, err
+}
+
+// formatFanStressResult formats the summary.txt from a fan-stress run, including
+// the per-step pass/fail display and the analysis section (throttling, max temps, fan response).
+func formatFanStressResult(archivePath string) string {
+	if archivePath == "" {
+		return "No output produced."
+	}
+	runDir := strings.TrimSuffix(archivePath, ".tar.gz")
+	raw, err := os.ReadFile(filepath.Join(runDir, "summary.txt"))
+	if err != nil {
+		return "Archive written to " + archivePath
+	}
+	content := strings.TrimSpace(string(raw))
+	kv := parseKeyValueSummary(content)
+
+	var b strings.Builder
+	b.WriteString(formatSATDetail(content))
+
+	// Append analysis section.
+	var analysis []string
+	if v, ok := kv["throttling_detected"]; ok {
+		label := "NO"
+		if v == "true" {
+			label = "YES  ← throttling detected during load"
+		}
+		analysis = append(analysis, "Throttling:   "+label)
+	}
+	if v, ok := kv["max_gpu_temp_c"]; ok && v != "0.0" {
+		analysis = append(analysis, "Max GPU temp: "+v+"°C")
+	}
+	if v, ok := kv["max_cpu_temp_c"]; ok && v != "0.0" {
+		analysis = append(analysis, "Max CPU temp: "+v+"°C")
+	}
+	if v, ok := kv["fan_response_sec"]; ok && v != "N/A" && v != "-1.0" {
+		analysis = append(analysis, "Fan response: "+v+"s")
+	}
+
+	if len(analysis) > 0 {
+		b.WriteString("\n\n=== Analysis ===\n")
+		for _, line := range analysis {
+			b.WriteString(line + "\n")
+		}
+	}
+	return strings.TrimSpace(b.String())
+}
+
 // satResultBody reads summary.txt from the SAT run directory (archive path without .tar.gz)
 // and returns a formatted human-readable result. Falls back to a plain message if unreadable.
 func satResultBody(archivePath string) string {

audit/internal/app/app_test.go

@@ -170,6 +170,10 @@ func (f fakeSAT) RunAMDAcceptancePack(baseDir string) (string, error) {
 	return "", nil
 }
 
+func (f fakeSAT) RunFanStressTest(_ context.Context, _ string, _ platform.FanStressOptions) (string, error) {
+	return "", nil
+}
+
 func TestNetworkStatusFormatsInterfacesAndRoute(t *testing.T) {
 	t.Parallel()
 

audit/internal/platform/sat_fan_stress.go

@@ -0,0 +1,587 @@
+package platform
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+)
+
+// FanStressOptions configures the fan-stress / thermal cycling test.
+type FanStressOptions struct {
+	BaselineSec  int   // idle monitoring before and after load (default 30)
+	Phase1DurSec int   // first load phase duration in seconds (default 300)
+	PauseSec     int   // pause between the two load phases (default 60)
+	Phase2DurSec int   // second load phase duration in seconds (default 300)
+	SizeMB       int   // GPU memory to allocate per GPU during stress (default 64)
+	GPUIndices   []int // which GPU indices to stress (empty = all detected)
+}
+
+// FanReading holds one fan sensor reading.
+type FanReading struct {
+	Name string
+	RPM  float64
+}
+
+// GPUStressMetric holds per-GPU metrics during the stress test.
+type GPUStressMetric struct {
+	Index     int
+	TempC     float64
+	UsagePct  float64
+	PowerW    float64
+	ClockMHz  float64
+	Throttled bool // true if any throttle reason is active
+}
+
+// FanStressRow is one second-interval telemetry sample covering all monitored dimensions.
+type FanStressRow struct {
+	TimestampUTC string
+	ElapsedSec   float64
+	Phase        string // "baseline", "load1", "pause", "load2", "cooldown"
+	GPUs         []GPUStressMetric
+	Fans         []FanReading
+	CPUMaxTempC  float64 // highest CPU temperature from ipmitool / sensors
+	SysPowerW    float64 // DCMI system power reading
+}
+
+// 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.
+func (s *System) RunFanStressTest(ctx context.Context, baseDir string, opts FanStressOptions) (string, error) {
+	if baseDir == "" {
+		baseDir = "/var/log/bee-sat"
+	}
+	applyFanStressDefaults(&opts)
+
+	ts := time.Now().UTC().Format("20060102-150405")
+	runDir := filepath.Join(baseDir, "fan-stress-"+ts)
+	if err := os.MkdirAll(runDir, 0755); err != nil {
+		return "", err
+	}
+	verboseLog := filepath.Join(runDir, "verbose.log")
+
+	// Phase name shared between sampler goroutine and main goroutine.
+	var phaseMu sync.Mutex
+	currentPhase := "init"
+	setPhase := func(name string) {
+		phaseMu.Lock()
+		currentPhase = name
+		phaseMu.Unlock()
+	}
+	getPhase := func() string {
+		phaseMu.Lock()
+		defer phaseMu.Unlock()
+		return currentPhase
+	}
+
+	start := time.Now()
+	var rowsMu sync.Mutex
+	var allRows []FanStressRow
+
+	// Start background sampler (every second).
+	stopCh := make(chan struct{})
+	doneCh := make(chan struct{})
+	go func() {
+		defer close(doneCh)
+		ticker := time.NewTicker(time.Second)
+		defer ticker.Stop()
+		for {
+			select {
+			case <-stopCh:
+				return
+			case <-ticker.C:
+				row := sampleFanStressRow(opts.GPUIndices, getPhase(), time.Since(start).Seconds())
+				rowsMu.Lock()
+				allRows = append(allRows, row)
+				rowsMu.Unlock()
+			}
+		}
+	}()
+
+	var summary strings.Builder
+	fmt.Fprintf(&summary, "run_at_utc=%s\n", time.Now().UTC().Format(time.RFC3339))
+
+	stats := satStats{}
+
+	// idlePhase sleeps for durSec while the sampler stamps phaseName on each row.
+	idlePhase := func(phaseName, stepName string, durSec int) {
+		if ctx.Err() != nil {
+			return
+		}
+		setPhase(phaseName)
+		appendSATVerboseLog(verboseLog,
+			fmt.Sprintf("[%s] start %s (idle %ds)", time.Now().UTC().Format(time.RFC3339), stepName, durSec),
+		)
+		select {
+		case <-ctx.Done():
+		case <-time.After(time.Duration(durSec) * time.Second):
+		}
+		appendSATVerboseLog(verboseLog,
+			fmt.Sprintf("[%s] finish %s", time.Now().UTC().Format(time.RFC3339), stepName),
+		)
+		fmt.Fprintf(&summary, "%s_status=OK\n", stepName)
+		stats.OK++
+	}
+
+	// loadPhase runs bee-gpu-stress for durSec; sampler stamps phaseName on each row.
+	loadPhase := func(phaseName, stepName string, durSec int) {
+		if ctx.Err() != nil {
+			return
+		}
+		setPhase(phaseName)
+		var env []string
+		if len(opts.GPUIndices) > 0 {
+			ids := make([]string, len(opts.GPUIndices))
+			for i, idx := range opts.GPUIndices {
+				ids[i] = strconv.Itoa(idx)
+			}
+			env = []string{"CUDA_VISIBLE_DEVICES=" + strings.Join(ids, ",")}
+		}
+		cmd := []string{
+			"bee-gpu-stress",
+			"--seconds", strconv.Itoa(durSec),
+			"--size-mb", strconv.Itoa(opts.SizeMB),
+		}
+		out, err := runSATCommandCtx(ctx, verboseLog, stepName, cmd, env)
+		_ = os.WriteFile(filepath.Join(runDir, stepName+".log"), out, 0644)
+		if err != nil && err != context.Canceled && err.Error() != "signal: killed" {
+			fmt.Fprintf(&summary, "%s_status=FAILED\n", stepName)
+			stats.Failed++
+		} else {
+			fmt.Fprintf(&summary, "%s_status=OK\n", stepName)
+			stats.OK++
+		}
+	}
+
+	// Execute test phases.
+	idlePhase("baseline", "01-baseline", opts.BaselineSec)
+	loadPhase("load1", "02-load1", opts.Phase1DurSec)
+	idlePhase("pause", "03-pause", opts.PauseSec)
+	loadPhase("load2", "04-load2", opts.Phase2DurSec)
+	idlePhase("cooldown", "05-cooldown", opts.BaselineSec)
+
+	// Stop sampler and collect rows.
+	close(stopCh)
+	<-doneCh
+
+	rowsMu.Lock()
+	rows := allRows
+	rowsMu.Unlock()
+
+	// Analysis.
+	throttled := analyzeThrottling(rows)
+	maxGPUTemp := analyzeMaxTemp(rows, func(r FanStressRow) float64 {
+		var m float64
+		for _, g := range r.GPUs {
+			if g.TempC > m {
+				m = g.TempC
+			}
+		}
+		return m
+	})
+	maxCPUTemp := analyzeMaxTemp(rows, func(r FanStressRow) float64 {
+		return r.CPUMaxTempC
+	})
+	fanResponseSec := analyzeFanResponse(rows)
+
+	fmt.Fprintf(&summary, "throttling_detected=%v\n", throttled)
+	fmt.Fprintf(&summary, "max_gpu_temp_c=%.1f\n", maxGPUTemp)
+	fmt.Fprintf(&summary, "max_cpu_temp_c=%.1f\n", maxCPUTemp)
+	if fanResponseSec >= 0 {
+		fmt.Fprintf(&summary, "fan_response_sec=%.1f\n", fanResponseSec)
+	} else {
+		fmt.Fprintf(&summary, "fan_response_sec=N/A\n")
+	}
+
+	// Throttling failure counts against overall result.
+	if throttled {
+		stats.Failed++
+	}
+	writeSATStats(&summary, stats)
+
+	// Write CSV outputs.
+	if err := WriteFanStressCSV(filepath.Join(runDir, "metrics.csv"), rows, opts.GPUIndices); err != nil {
+		return "", err
+	}
+	_ = WriteFanSensorsCSV(filepath.Join(runDir, "fan-sensors.csv"), rows)
+
+	if err := os.WriteFile(filepath.Join(runDir, "summary.txt"), []byte(summary.String()), 0644); err != nil {
+		return "", err
+	}
+
+	archive := filepath.Join(baseDir, "fan-stress-"+ts+".tar.gz")
+	if err := createTarGz(archive, runDir); err != nil {
+		return "", err
+	}
+	return archive, nil
+}
+
+func applyFanStressDefaults(opts *FanStressOptions) {
+	if opts.BaselineSec <= 0 {
+		opts.BaselineSec = 30
+	}
+	if opts.Phase1DurSec <= 0 {
+		opts.Phase1DurSec = 300
+	}
+	if opts.PauseSec <= 0 {
+		opts.PauseSec = 60
+	}
+	if opts.Phase2DurSec <= 0 {
+		opts.Phase2DurSec = 300
+	}
+	if opts.SizeMB <= 0 {
+		opts.SizeMB = 64
+	}
+}
+
+// sampleFanStressRow collects all metrics for one telemetry sample.
+func sampleFanStressRow(gpuIndices []int, phase string, elapsed float64) FanStressRow {
+	row := FanStressRow{
+		TimestampUTC: time.Now().UTC().Format(time.RFC3339),
+		ElapsedSec:   elapsed,
+		Phase:        phase,
+	}
+	row.GPUs = sampleGPUStressMetrics(gpuIndices)
+	row.Fans, _ = sampleFanSpeeds()
+	row.CPUMaxTempC = sampleCPUMaxTemp()
+	row.SysPowerW = sampleSystemPower()
+	return row
+}
+
+// sampleGPUStressMetrics queries nvidia-smi for temperature, utilization, power,
+// clock frequency, and active throttle reasons for each GPU.
+func sampleGPUStressMetrics(gpuIndices []int) []GPUStressMetric {
+	args := []string{
+		"--query-gpu=index,temperature.gpu,utilization.gpu,power.draw,clocks.current.graphics,clocks_throttle_reasons.active",
+		"--format=csv,noheader,nounits",
+	}
+	if len(gpuIndices) > 0 {
+		ids := make([]string, len(gpuIndices))
+		for i, idx := range gpuIndices {
+			ids[i] = strconv.Itoa(idx)
+		}
+		args = append([]string{"--id=" + strings.Join(ids, ",")}, args...)
+	}
+	out, err := exec.Command("nvidia-smi", args...).Output()
+	if err != nil {
+		return nil
+	}
+	var metrics []GPUStressMetric
+	for _, line := range strings.Split(strings.TrimSpace(string(out)), "\n") {
+		line = strings.TrimSpace(line)
+		if line == "" {
+			continue
+		}
+		parts := strings.Split(line, ", ")
+		if len(parts) < 6 {
+			continue
+		}
+		idx, _ := strconv.Atoi(strings.TrimSpace(parts[0]))
+		throttleVal := strings.TrimSpace(parts[5])
+		// Throttled if active reasons bitmask is non-zero.
+		throttled := throttleVal != "0x0000000000000000" &&
+			throttleVal != "0x0" &&
+			throttleVal != "0" &&
+			throttleVal != "" &&
+			throttleVal != "N/A"
+		metrics = append(metrics, GPUStressMetric{
+			Index:     idx,
+			TempC:     parseGPUFloat(parts[1]),
+			UsagePct:  parseGPUFloat(parts[2]),
+			PowerW:    parseGPUFloat(parts[3]),
+			ClockMHz:  parseGPUFloat(parts[4]),
+			Throttled: throttled,
+		})
+	}
+	return metrics
+}
+
+// sampleFanSpeeds reads fan RPM values from ipmitool sdr.
+func sampleFanSpeeds() ([]FanReading, error) {
+	out, err := exec.Command("ipmitool", "sdr", "type", "Fan").Output()
+	if err != nil {
+		return nil, err
+	}
+	return parseFanSpeeds(string(out)), nil
+}
+
+// parseFanSpeeds parses "ipmitool sdr type Fan" output.
+// Line format: "FAN1             | 2400.000   | RPM        | ok"
+func parseFanSpeeds(raw string) []FanReading {
+	var fans []FanReading
+	for _, line := range strings.Split(strings.TrimSpace(raw), "\n") {
+		parts := strings.Split(line, "|")
+		if len(parts) < 3 {
+			continue
+		}
+		unit := strings.TrimSpace(parts[2])
+		if !strings.EqualFold(unit, "RPM") {
+			continue
+		}
+		valStr := strings.TrimSpace(parts[1])
+		if strings.EqualFold(valStr, "na") || strings.EqualFold(valStr, "disabled") || valStr == "" {
+			continue
+		}
+		val, err := strconv.ParseFloat(valStr, 64)
+		if err != nil {
+			continue
+		}
+		fans = append(fans, FanReading{
+			Name: strings.TrimSpace(parts[0]),
+			RPM:  val,
+		})
+	}
+	return fans
+}
+
+// sampleCPUMaxTemp returns the highest CPU/inlet temperature from ipmitool or sensors.
+func sampleCPUMaxTemp() float64 {
+	out, err := exec.Command("ipmitool", "sdr", "type", "Temperature").Output()
+	if err != nil {
+		return sampleCPUTempViaSensors()
+	}
+	return parseIPMIMaxTemp(string(out))
+}
+
+// parseIPMIMaxTemp extracts the maximum temperature from "ipmitool sdr type Temperature".
+func parseIPMIMaxTemp(raw string) float64 {
+	var max float64
+	for _, line := range strings.Split(strings.TrimSpace(raw), "\n") {
+		parts := strings.Split(line, "|")
+		if len(parts) < 3 {
+			continue
+		}
+		unit := strings.TrimSpace(parts[2])
+		if !strings.Contains(strings.ToLower(unit), "degrees") {
+			continue
+		}
+		valStr := strings.TrimSpace(parts[1])
+		if strings.EqualFold(valStr, "na") || valStr == "" {
+			continue
+		}
+		val, err := strconv.ParseFloat(valStr, 64)
+		if err != nil {
+			continue
+		}
+		if val > max {
+			max = val
+		}
+	}
+	return max
+}
+
+// sampleCPUTempViaSensors falls back to lm-sensors when ipmitool is unavailable.
+func sampleCPUTempViaSensors() float64 {
+	out, err := exec.Command("sensors", "-u").Output()
+	if err != nil {
+		return 0
+	}
+	var max float64
+	for _, line := range strings.Split(string(out), "\n") {
+		line = strings.TrimSpace(line)
+		fields := strings.Fields(line)
+		if len(fields) < 2 {
+			continue
+		}
+		if !strings.HasSuffix(fields[0], "_input:") {
+			continue
+		}
+		val, err := strconv.ParseFloat(fields[1], 64)
+		if err != nil {
+			continue
+		}
+		if val > 0 && val < 150 && val > max {
+			max = val
+		}
+	}
+	return max
+}
+
+// sampleSystemPower reads system power draw via DCMI.
+func sampleSystemPower() float64 {
+	out, err := exec.Command("ipmitool", "dcmi", "power", "reading").Output()
+	if err != nil {
+		return 0
+	}
+	return parseDCMIPowerReading(string(out))
+}
+
+// parseDCMIPowerReading extracts the instantaneous power reading from ipmitool dcmi output.
+// Sample: "    Instantaneous power reading:                   500 Watts"
+func parseDCMIPowerReading(raw string) float64 {
+	for _, line := range strings.Split(raw, "\n") {
+		if !strings.Contains(strings.ToLower(line), "instantaneous") {
+			continue
+		}
+		parts := strings.Fields(line)
+		for i, p := range parts {
+			if strings.EqualFold(p, "Watts") && i > 0 {
+				val, err := strconv.ParseFloat(parts[i-1], 64)
+				if err == nil {
+					return val
+				}
+			}
+		}
+	}
+	return 0
+}
+
+// analyzeThrottling returns true if any GPU reported an active throttle reason
+// during either load phase.
+func analyzeThrottling(rows []FanStressRow) bool {
+	for _, row := range rows {
+		if row.Phase != "load1" && row.Phase != "load2" {
+			continue
+		}
+		for _, gpu := range row.GPUs {
+			if gpu.Throttled {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+// analyzeMaxTemp returns the maximum value of the given extractor across all rows.
+func analyzeMaxTemp(rows []FanStressRow, extract func(FanStressRow) float64) float64 {
+	var max float64
+	for _, row := range rows {
+		if v := extract(row); v > max {
+			max = v
+		}
+	}
+	return max
+}
+
+// analyzeFanResponse returns the seconds from load1 start until fan RPM first
+// increased by more than 5% above the baseline average. Returns -1 if undetermined.
+func analyzeFanResponse(rows []FanStressRow) float64 {
+	// Compute baseline average fan RPM.
+	var baseTotal, baseCount float64
+	for _, row := range rows {
+		if row.Phase != "baseline" {
+			continue
+		}
+		for _, f := range row.Fans {
+			baseTotal += f.RPM
+			baseCount++
+		}
+	}
+	if baseCount == 0 || baseTotal == 0 {
+		return -1
+	}
+	baseAvg := baseTotal / baseCount
+	threshold := baseAvg * 1.05 // 5% increase signals fan ramp-up
+
+	// Find elapsed time when load1 started.
+	var load1Start float64 = -1
+	for _, row := range rows {
+		if row.Phase == "load1" {
+			load1Start = row.ElapsedSec
+			break
+		}
+	}
+	if load1Start < 0 {
+		return -1
+	}
+
+	// Find first load1 row where average RPM crosses the threshold.
+	for _, row := range rows {
+		if row.Phase != "load1" {
+			continue
+		}
+		var total, count float64
+		for _, f := range row.Fans {
+			total += f.RPM
+			count++
+		}
+		if count > 0 && total/count >= threshold {
+			return row.ElapsedSec - load1Start
+		}
+	}
+	return -1
+}
+
+// WriteFanStressCSV writes the wide-format metrics CSV with one row per second.
+// GPU columns are generated per index in gpuIndices order.
+func WriteFanStressCSV(path string, rows []FanStressRow, gpuIndices []int) error {
+	if len(rows) == 0 {
+		return os.WriteFile(path, []byte("no data\n"), 0644)
+	}
+
+	var b strings.Builder
+
+	// Header: fixed system columns + per-GPU columns.
+	b.WriteString("timestamp_utc,elapsed_sec,phase,fan_avg_rpm,fan_min_rpm,fan_max_rpm,cpu_max_temp_c,sys_power_w")
+	for _, idx := range gpuIndices {
+		fmt.Fprintf(&b, ",gpu%d_temp_c,gpu%d_usage_pct,gpu%d_power_w,gpu%d_clock_mhz,gpu%d_throttled",
+			idx, idx, idx, idx, idx)
+	}
+	b.WriteRune('\n')
+
+	for _, row := range rows {
+		favg, fmin, fmax := fanRPMStats(row.Fans)
+		fmt.Fprintf(&b, "%s,%.1f,%s,%.0f,%.0f,%.0f,%.1f,%.1f",
+			row.TimestampUTC,
+			row.ElapsedSec,
+			row.Phase,
+			favg, fmin, fmax,
+			row.CPUMaxTempC,
+			row.SysPowerW,
+		)
+		gpuByIdx := make(map[int]GPUStressMetric, len(row.GPUs))
+		for _, g := range row.GPUs {
+			gpuByIdx[g.Index] = g
+		}
+		for _, idx := range gpuIndices {
+			g := gpuByIdx[idx]
+			throttled := 0
+			if g.Throttled {
+				throttled = 1
+			}
+			fmt.Fprintf(&b, ",%.1f,%.1f,%.1f,%.0f,%d",
+				g.TempC, g.UsagePct, g.PowerW, g.ClockMHz, throttled)
+		}
+		b.WriteRune('\n')
+	}
+
+	return os.WriteFile(path, []byte(b.String()), 0644)
+}
+
+// WriteFanSensorsCSV writes individual fan sensor readings in long (tidy) format.
+func WriteFanSensorsCSV(path string, rows []FanStressRow) error {
+	var b strings.Builder
+	b.WriteString("timestamp_utc,elapsed_sec,phase,fan_name,rpm\n")
+	for _, row := range rows {
+		for _, f := range row.Fans {
+			fmt.Fprintf(&b, "%s,%.1f,%s,%s,%.0f\n",
+				row.TimestampUTC, row.ElapsedSec, row.Phase, f.Name, f.RPM)
+		}
+	}
+	return os.WriteFile(path, []byte(b.String()), 0644)
+}
+
+// fanRPMStats computes average, min, max RPM across all fans in a sample row.
+func fanRPMStats(fans []FanReading) (avg, min, max float64) {
+	if len(fans) == 0 {
+		return 0, 0, 0
+	}
+	min = fans[0].RPM
+	max = fans[0].RPM
+	var total float64
+	for _, f := range fans {
+		total += f.RPM
+		if f.RPM < min {
+			min = f.RPM
+		}
+		if f.RPM > max {
+			max = f.RPM
+		}
+	}
+	return total / float64(len(fans)), min, max
+}

audit/internal/tui/forms.go

@@ -1,8 +1,10 @@
 package tui
 
 import (
+	"context"
 	"time"
 
+	"bee/audit/internal/platform"
 	tea "github.com/charmbracelet/bubbletea"
 )
 
@@ -137,6 +139,21 @@ func (m model) updateConfirm(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 				},
 				pollSATProgress("gpu-amd", since),
 			)
+		case actionRunFanStress:
+			m.busyTitle = "Fan Stress Test"
+			m.progressPrefix = "fan-stress"
+			m.progressSince = time.Now()
+			m.progressLines = nil
+			since := m.progressSince
+			opts := hcFanStressOpts(m.hcMode, m.app)
+			return m, tea.Batch(
+				func() tea.Msg {
+					ctx := context.Background()
+					result, err := m.app.RunFanStressTestResult(ctx, opts)
+					return resultMsg{title: result.Title, body: result.Body, err: err, back: screenHealthCheck}
+				},
+				pollSATProgress("fan-stress", since),
+			)
 		}
 	case "ctrl+c":
 		return m, tea.Quit
@@ -148,9 +165,53 @@ func (m model) confirmCancelTarget() screen {
 	switch m.pendingAction {
 	case actionExportBundle:
 		return screenExportTargets
-	case actionRunAll, actionRunMemorySAT, actionRunStorageSAT, actionRunCPUSAT, actionRunAMDGPUSAT:
+	case actionRunAll, actionRunMemorySAT, actionRunStorageSAT, actionRunCPUSAT, actionRunAMDGPUSAT, actionRunFanStress:
 		return screenHealthCheck
 	default:
 		return screenMain
 	}
 }
+
+// hcFanStressOpts builds FanStressOptions for the selected mode, auto-detecting all GPUs.
+func hcFanStressOpts(hcMode int, application interface {
+	ListNvidiaGPUs() ([]platform.NvidiaGPU, error)
+}) platform.FanStressOptions {
+	// Phase durations per mode: [baseline, load1, pause, load2]
+	type durations struct{ baseline, load1, pause, load2 int }
+	modes := [3]durations{
+		{30, 120, 30, 120},   // Quick:    ~5 min total
+		{60, 300, 60, 300},   // Standard: ~12 min total
+		{60, 600, 120, 600},  // Express:  ~24 min total
+	}
+	if hcMode < 0 || hcMode >= len(modes) {
+		hcMode = 0
+	}
+	d := modes[hcMode]
+
+	// Use all detected NVIDIA GPUs.
+	var indices []int
+	if gpus, err := application.ListNvidiaGPUs(); err == nil {
+		for _, g := range gpus {
+			indices = append(indices, g.Index)
+		}
+	}
+
+	// Use minimum GPU memory size to fit all GPUs.
+	sizeMB := 64
+	if gpus, err := application.ListNvidiaGPUs(); err == nil {
+		for _, g := range gpus {
+			if g.MemoryMB > 0 && (sizeMB == 64 || g.MemoryMB < sizeMB) {
+				sizeMB = g.MemoryMB / 16 // allocate 1/16 of VRAM per GPU
+			}
+		}
+	}
+
+	return platform.FanStressOptions{
+		BaselineSec:  d.baseline,
+		Phase1DurSec: d.load1,
+		PauseSec:     d.pause,
+		Phase2DurSec: d.load2,
+		SizeMB:       sizeMB,
+		GPUIndices:   indices,
+	}
+}

audit/internal/tui/screen_health_check.go

@@ -18,16 +18,17 @@ const (
 
 // Cursor positions in Health Check screen.
 const (
-	hcCurGPU       = 0
+	hcCurGPU        = 0
-	hcCurMemory    = 1
+	hcCurMemory     = 1
-	hcCurStorage   = 2
+	hcCurStorage    = 2
-	hcCurCPU       = 3
+	hcCurCPU        = 3
-	hcCurSelectAll = 4
+	hcCurSelectAll  = 4
-	hcCurModeQuick = 5
+	hcCurModeQuick  = 5
-	hcCurModeStd   = 6
+	hcCurModeStd    = 6
-	hcCurModeExpr  = 7
+	hcCurModeExpr   = 7
-	hcCurRunAll    = 8
+	hcCurRunAll     = 8
-	hcCurTotal     = 9
+	hcCurFanStress  = 9
+	hcCurTotal      = 10
 )
 
 // hcModeDurations maps mode index (0=Quick,1=Standard,2=Express) to GPU stress seconds.
@@ -82,6 +83,8 @@ func (m model) updateHealthCheck(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 			m.hcMode = m.hcCursor - hcCurModeQuick
 		case hcCurRunAll:
 			return m.hcRunAll()
+		case hcCurFanStress:
+			return m.hcRunFanStress()
 		}
 	case "g", "G":
 		return m.hcRunSingle(hcGPU)
@@ -93,6 +96,8 @@ func (m model) updateHealthCheck(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 		return m.hcRunSingle(hcCPU)
 	case "r", "R":
 		return m.hcRunAll()
+	case "f", "F":
+		return m.hcRunFanStress()
 	case "a", "A":
 		allOn := m.hcSel[0] && m.hcSel[1] && m.hcSel[2] && m.hcSel[3]
 		for i := range m.hcSel {
@@ -143,6 +148,13 @@ func (m model) hcRunSingle(idx int) (tea.Model, tea.Cmd) {
 	return m, nil
 }
 
+func (m model) hcRunFanStress() (tea.Model, tea.Cmd) {
+	m.pendingAction = actionRunFanStress
+	m.screen = screenConfirm
+	m.cursor = 0
+	return m, nil
+}
+
 func (m model) hcRunAll() (tea.Model, tea.Cmd) {
 	for _, sel := range m.hcSel {
 		if sel {
@@ -300,8 +312,16 @@ func renderHealthCheck(m model) string {
 		fmt.Fprintf(&b, "%s[ RUN ALL [R] ]\n", pfx)
 	}
 
+	{
+		pfx := "  "
+		if m.hcCursor == hcCurFanStress {
+			pfx = "> "
+		}
+		fmt.Fprintf(&b, "%s[ FAN STRESS TEST [F] ]   (thermal cycling, fan lag, throttle check)\n", pfx)
+	}
+
 	fmt.Fprintln(&b)
 	fmt.Fprintln(&b, "─────────────────────────────────────────────────────────────────")
-	fmt.Fprint(&b, "[↑↓] move  [space/enter] toggle  [letter] single test  [R] run all  [Esc] back")
+	fmt.Fprint(&b, "[↑↓] move  [space/enter] toggle  [letter] single test  [R] run all  [F] fan stress  [Esc] back")
 	return b.String()
 }

audit/internal/tui/types.go

@@ -40,7 +40,8 @@ const (
 	actionRunMemorySAT  actionKind = "run_memory_sat"
 	actionRunStorageSAT actionKind = "run_storage_sat"
 	actionRunCPUSAT     actionKind = "run_cpu_sat"
-	actionRunAMDGPUSAT  actionKind = "run_amd_gpu_sat"
+	actionRunAMDGPUSAT   actionKind = "run_amd_gpu_sat"
+	actionRunFanStress   actionKind = "run_fan_stress"
 )
 
 type model struct {
@@ -188,6 +189,11 @@ func (m model) confirmBody() (string, string) {
 		return "CPU test", "Run stress-ng? Mode: " + modes[m.hcMode]
 	case actionRunAMDGPUSAT:
 		return "AMD GPU test", "Run AMD GPU diagnostic pack (rocm-smi)?"
+	case actionRunFanStress:
+		modes := []string{"Quick (2×2min)", "Standard (2×5min)", "Express (2×10min)"}
+		return "Fan Stress Test", "Two-phase GPU thermal cycling test.\n" +
+			"Monitors fans, temps, power — detects throttling.\n" +
+			"Mode: " + modes[m.hcMode] + "\n\nAll NVIDIA GPUs will be stressed."
 	default:
 		return "Confirm", "Proceed?"
 	}