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()