diff --git a/cmd/sdrd/main.go b/cmd/sdrd/main.go
index a312b3c..bcfa178 100644
--- a/cmd/sdrd/main.go
+++ b/cmd/sdrd/main.go
@@ -12,8 +12,6 @@ import (
 	"path/filepath"
 	"runtime/debug"
 	"sort"
-
-	"sdr-visual-suite/internal/config"
 	"strconv"
 	"strings"
 	"sync"
@@ -23,6 +21,7 @@ import (
 	"github.com/gorilla/websocket"
 
 	"sdr-visual-suite/internal/classifier"
+	"sdr-visual-suite/internal/config"
 	"sdr-visual-suite/internal/detector"
 	"sdr-visual-suite/internal/dsp"
 	"sdr-visual-suite/internal/events"
@@ -853,7 +852,7 @@ func runDSP(ctx context.Context, srcMgr *sourceManager, cfg config.Config, det *
 			}
 			eventMu.Unlock()
 			if rec != nil {
-				rec.OnEvents(finished)
+				go rec.OnEvents(finished)
 			}
 			h.broadcast(SpectrumFrame{
 				Timestamp: now.UnixMilli(),
diff --git a/internal/config/config.go b/internal/config/config.go
index 43578ef..48e21b4 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -115,6 +115,11 @@ func Default() Config {
 
 func Load(path string) (Config, error) {
 	cfg := Default()
+	if b, err := os.ReadFile(autosavePath(path)); err == nil {
+		if err := yaml.Unmarshal(b, &cfg); err == nil {
+			return applyDefaults(cfg), nil
+		}
+	}
 	b, err := os.ReadFile(path)
 	if err != nil {
 		return cfg, err
@@ -122,6 +127,10 @@ func Load(path string) (Config, error) {
 	if err := yaml.Unmarshal(b, &cfg); err != nil {
 		return cfg, err
 	}
+	return applyDefaults(cfg), nil
+}
+
+func applyDefaults(cfg Config) Config {
 	if cfg.Detector.MinDurationMs <= 0 {
 		cfg.Detector.MinDurationMs = 250
 	}
@@ -182,7 +191,7 @@ func Load(path string) (Config, error) {
 	if cfg.Recorder.RingSeconds <= 0 {
 		cfg.Recorder.RingSeconds = 8
 	}
-	return cfg, nil
+	return cfg
 }
 
 func (c Config) FrameInterval() time.Duration {
diff --git a/internal/config/save.go b/internal/config/save.go
index a81358f..3d630d9 100644
--- a/internal/config/save.go
+++ b/internal/config/save.go
@@ -2,15 +2,27 @@ package config
 
 import (
 	"os"
+	"path/filepath"
+	"strings"
 
 	"gopkg.in/yaml.v3"
 )
 
-// Save writes the current config back to disk.
+// Save writes the current config to an autosave file to preserve the original YAML formatting/comments.
+// Autosave path: <path without ext>.autosave<ext>
 func Save(path string, cfg Config) error {
 	b, err := yaml.Marshal(cfg)
 	if err != nil {
 		return err
 	}
-	return os.WriteFile(path, b, 0o644)
+	return os.WriteFile(autosavePath(path), b, 0o644)
+}
+
+func autosavePath(path string) string {
+	ext := filepath.Ext(path)
+	if ext == "" {
+		return path + ".autosave"
+	}
+	base := strings.TrimSuffix(path, ext)
+	return base + ".autosave" + ext
 }
diff --git a/internal/detector/detector.go b/internal/detector/detector.go
index 8f1f469..57222a4 100644
--- a/internal/detector/detector.go
+++ b/internal/detector/detector.go
@@ -257,6 +257,7 @@ func (d *Detector) smoothSpectrum(spectrum []float64) []float64 {
 		v := spectrum[i]
 		d.ema[i] = alpha*v + (1-alpha)*d.ema[i]
 	}
+	// IMPORTANT: caller must not modify returned slice
 	return d.ema
 }
 
diff --git a/internal/runtime/runtime.go b/internal/runtime/runtime.go
index 428594f..6e41579 100644
--- a/internal/runtime/runtime.go
+++ b/internal/runtime/runtime.go
@@ -2,6 +2,7 @@ package runtime
 
 import (
 	"errors"
+	"math"
 	"sync"
 
 	"sdr-visual-suite/internal/config"
@@ -131,15 +132,29 @@ func (m *Manager) ApplyConfig(update ConfigUpdate) (config.Config, error) {
 			next.Detector.HoldMs = *update.Detector.HoldMs
 		}
 		if update.Detector.EmaAlpha != nil {
-			next.Detector.EmaAlpha = *update.Detector.EmaAlpha
+			v := *update.Detector.EmaAlpha
+			if math.IsNaN(v) || math.IsInf(v, 0) || v < 0 || v > 1 {
+				return m.cfg, errors.New("ema_alpha must be between 0 and 1")
+			}
+			next.Detector.EmaAlpha = v
 		}
 		if update.Detector.HysteresisDb != nil {
-			next.Detector.HysteresisDb = *update.Detector.HysteresisDb
+			v := *update.Detector.HysteresisDb
+			if math.IsNaN(v) || math.IsInf(v, 0) || v < 0 {
+				return m.cfg, errors.New("hysteresis_db must be >= 0")
+			}
+			next.Detector.HysteresisDb = v
 		}
 		if update.Detector.MinStableFrames != nil {
+			if *update.Detector.MinStableFrames < 1 {
+				return m.cfg, errors.New("min_stable_frames must be >= 1")
+			}
 			next.Detector.MinStableFrames = *update.Detector.MinStableFrames
 		}
 		if update.Detector.GapToleranceMs != nil {
+			if *update.Detector.GapToleranceMs < 0 {
+				return m.cfg, errors.New("gap_tolerance_ms must be >= 0")
+			}
 			next.Detector.GapToleranceMs = *update.Detector.GapToleranceMs
 		}
 		if update.Detector.CFAREnabled != nil {
diff --git a/internal/runtime/runtime_test.go b/internal/runtime/runtime_test.go
index 9bed40b..00c949b 100644
--- a/internal/runtime/runtime_test.go
+++ b/internal/runtime/runtime_test.go
@@ -72,14 +72,72 @@ func TestApplyConfigUpdate(t *testing.T) {
 
 func TestApplyConfigRejectsInvalid(t *testing.T) {
 	cfg := config.Default()
-	mgr := New(cfg)
-	bad := 0
-	if _, err := mgr.ApplyConfig(ConfigUpdate{SampleRate: &bad}); err == nil {
-		t.Fatalf("expected error")
+
+	{
+		mgr := New(cfg)
+		bad := 0
+		if _, err := mgr.ApplyConfig(ConfigUpdate{SampleRate: &bad}); err == nil {
+			t.Fatalf("expected error")
+		}
+		snap := mgr.Snapshot()
+		if snap.SampleRate != cfg.SampleRate {
+			t.Fatalf("sample rate changed on error")
+		}
+	}
+
+	{
+		mgr := New(cfg)
+		badAlpha := -0.5
+		if _, err := mgr.ApplyConfig(ConfigUpdate{Detector: &DetectorUpdate{EmaAlpha: &badAlpha}}); err == nil {
+			t.Fatalf("expected ema_alpha error")
+		}
+		if mgr.Snapshot().Detector.EmaAlpha != cfg.Detector.EmaAlpha {
+			t.Fatalf("ema_alpha changed on error")
+		}
+	}
+
+	{
+		mgr := New(cfg)
+		badAlpha := 1.5
+		if _, err := mgr.ApplyConfig(ConfigUpdate{Detector: &DetectorUpdate{EmaAlpha: &badAlpha}}); err == nil {
+			t.Fatalf("expected ema_alpha upper bound error")
+		}
+		if mgr.Snapshot().Detector.EmaAlpha != cfg.Detector.EmaAlpha {
+			t.Fatalf("ema_alpha changed on error")
+		}
 	}
-	snap := mgr.Snapshot()
-	if snap.SampleRate != cfg.SampleRate {
-		t.Fatalf("sample rate changed on error")
+
+	{
+		mgr := New(cfg)
+		badHyst := -1.0
+		if _, err := mgr.ApplyConfig(ConfigUpdate{Detector: &DetectorUpdate{HysteresisDb: &badHyst}}); err == nil {
+			t.Fatalf("expected hysteresis_db error")
+		}
+		if mgr.Snapshot().Detector.HysteresisDb != cfg.Detector.HysteresisDb {
+			t.Fatalf("hysteresis_db changed on error")
+		}
+	}
+
+	{
+		mgr := New(cfg)
+		badStable := 0
+		if _, err := mgr.ApplyConfig(ConfigUpdate{Detector: &DetectorUpdate{MinStableFrames: &badStable}}); err == nil {
+			t.Fatalf("expected min_stable_frames error")
+		}
+		if mgr.Snapshot().Detector.MinStableFrames != cfg.Detector.MinStableFrames {
+			t.Fatalf("min_stable_frames changed on error")
+		}
+	}
+
+	{
+		mgr := New(cfg)
+		badGap := -10
+		if _, err := mgr.ApplyConfig(ConfigUpdate{Detector: &DetectorUpdate{GapToleranceMs: &badGap}}); err == nil {
+			t.Fatalf("expected gap_tolerance_ms error")
+		}
+		if mgr.Snapshot().Detector.GapToleranceMs != cfg.Detector.GapToleranceMs {
+			t.Fatalf("gap_tolerance_ms changed on error")
+		}
 	}
 }
 
diff --git a/web/app.js b/web/app.js
index 37bf491..9832faa 100644
--- a/web/app.js
+++ b/web/app.js
@@ -34,6 +34,8 @@ const cfarGuardInput = qs('cfarGuardInput');
 const cfarTrainInput = qs('cfarTrainInput');
 const cfarRankInput = qs('cfarRankInput');
 const cfarScaleInput = qs('cfarScaleInput');
+const minDurationInput = qs('minDurationInput');
+const holdInput = qs('holdInput');
 const emaAlphaInput = qs('emaAlphaInput');
 const hysteresisInput = qs('hysteresisInput');
 const stableFramesInput = qs('stableFramesInput');
@@ -83,6 +85,7 @@ const liveListenEventBtn = qs('liveListenEventBtn');
 const decodeEventBtn = qs('decodeEventBtn');
 const decodeModeSelect = qs('decodeMode');
 const recordingMetaEl = qs('recordingMeta');
+const decodeResultEl = qs('decodeResult');
 const recordingMetaLink = qs('recordingMetaLink');
 const recordingIQLink = qs('recordingIQLink');
 const recordingAudioLink = qs('recordingAudioLink');
@@ -98,6 +101,8 @@ const railTabs = Array.from(document.querySelectorAll('.rail-tab'));
 const tabPanels = Array.from(document.querySelectorAll('.tab-panel'));
 const presetButtons = Array.from(document.querySelectorAll('.preset-btn'));
 const liveListenBtn = qs('liveListenBtn');
+const listenSecondsInput = qs('listenSeconds');
+const listenModeSelect = qs('listenMode');
 
 let latest = null;
 let currentConfig = null;
@@ -113,6 +118,9 @@ let avgAlpha = 0;
 let avgSpectrum = null;
 let maxSpectrum = null;
 let lastFFTSize = null;
+let processedSpectrum = null;
+let processedSpectrumSource = null;
+let processingDirty = true;
 
 let pendingConfigUpdate = null;
 let pendingSettingsUpdate = null;
@@ -201,6 +209,10 @@ function maxInBinRange(spectrum, b0, b1) {
   return max;
 }
 
+function markSpectrumDirty() {
+  processingDirty = true;
+}
+
 function processSpectrum(spectrum) {
   if (!spectrum) return spectrum;
   let base = spectrum;
@@ -230,6 +242,18 @@ function processSpectrum(spectrum) {
 function resetProcessingCaches() {
   avgSpectrum = null;
   maxSpectrum = null;
+  processedSpectrum = null;
+  processedSpectrumSource = null;
+  processingDirty = true;
+}
+
+function getProcessedSpectrum() {
+  if (!latest?.spectrum_db) return null;
+  if (!processingDirty && processedSpectrumSource === latest.spectrum_db) return processedSpectrum;
+  processedSpectrum = processSpectrum(latest.spectrum_db);
+  processedSpectrumSource = latest.spectrum_db;
+  processingDirty = false;
+  return processedSpectrum;
 }
 
 function resizeCanvas(canvas) {
@@ -311,6 +335,7 @@ function applyConfigToUI(cfg) {
     if (recDecodeToggle) recDecodeToggle.checked = !!cfg.recorder.auto_decode;
     if (recMinSNR) recMinSNR.value = cfg.recorder.min_snr_db ?? 10;
     if (recMaxDisk) recMaxDisk.value = cfg.recorder.max_disk_mb ?? 0;
+    if (recClassFilter) recClassFilter.value = (cfg.recorder.class_filter || []).join(', ');
   }
   spanInput.value = (cfg.sample_rate / zoom / 1e6).toFixed(3);
   isSyncingConfig = false;
@@ -460,7 +485,8 @@ function renderBandNavigator() {
   const h = navCanvas.height;
   ctx.clearRect(0, 0, w, h);
 
-  const display = processSpectrum(latest.spectrum_db);
+  const display = getProcessedSpectrum();
+  if (!display) return;
   const minDb = -120;
   const maxDb = 0;
 
@@ -523,7 +549,8 @@ function renderSpectrum() {
   const h = spectrumCanvas.height;
   ctx.clearRect(0, 0, w, h);
 
-  const display = processSpectrum(latest.spectrum_db);
+  const display = getProcessedSpectrum();
+  if (!display) return;
   const n = display.length;
   const span = latest.sample_rate / zoom;
   const startHz = latest.center_hz - span / 2 + pan * span;
@@ -612,7 +639,8 @@ function renderWaterfall() {
   const prev = ctx.getImageData(0, 0, w, h - 1);
   ctx.putImageData(prev, 0, 1);
 
-  const display = processSpectrum(latest.spectrum_db);
+  const display = getProcessedSpectrum();
+  if (!display) return;
   const n = display.length;
   const span = latest.sample_rate / zoom;
   const startHz = latest.center_hz - span / 2 + pan * span;
@@ -766,7 +794,8 @@ function renderDetailSpectrogram() {
   ctx.fillRect(0, 0, w, h);
   if (!latest || !ev) return;
 
-  const display = processSpectrum(latest.spectrum_db);
+  const display = getProcessedSpectrum();
+  if (!display) return;
   const n = display.length;
   const localSpan = Math.min(latest.sample_rate, Math.max(ev.bandwidth_hz * 4, latest.sample_rate / 10));
   const startHz = ev.center_hz - localSpan / 2;
@@ -981,6 +1010,7 @@ function connect() {
   ws.onopen = () => setWsBadge('Live', 'ok');
   ws.onmessage = (ev) => {
     latest = JSON.parse(ev.data);
+    markSpectrumDirty();
     if (followLive) pan = 0;
     updateHeroMetrics();
     renderLists();
@@ -1163,6 +1193,30 @@ if (cfarScaleInput) cfarScaleInput.addEventListener('change', () => {
   const v = parseFloat(cfarScaleInput.value);
   if (Number.isFinite(v)) queueConfigUpdate({ detector: { cfar_scale_db: v } });
 });
+if (minDurationInput) minDurationInput.addEventListener('change', () => {
+  const v = parseInt(minDurationInput.value, 10);
+  if (Number.isFinite(v)) queueConfigUpdate({ detector: { min_duration_ms: v } });
+});
+if (holdInput) holdInput.addEventListener('change', () => {
+  const v = parseInt(holdInput.value, 10);
+  if (Number.isFinite(v)) queueConfigUpdate({ detector: { hold_ms: v } });
+});
+if (emaAlphaInput) emaAlphaInput.addEventListener('change', () => {
+  const v = parseFloat(emaAlphaInput.value);
+  if (Number.isFinite(v)) queueConfigUpdate({ detector: { ema_alpha: v } });
+});
+if (hysteresisInput) hysteresisInput.addEventListener('change', () => {
+  const v = parseFloat(hysteresisInput.value);
+  if (Number.isFinite(v)) queueConfigUpdate({ detector: { hysteresis_db: v } });
+});
+if (stableFramesInput) stableFramesInput.addEventListener('change', () => {
+  const v = parseInt(stableFramesInput.value, 10);
+  if (Number.isFinite(v)) queueConfigUpdate({ detector: { min_stable_frames: v } });
+});
+if (gapToleranceInput) gapToleranceInput.addEventListener('change', () => {
+  const v = parseInt(gapToleranceInput.value, 10);
+  if (Number.isFinite(v)) queueConfigUpdate({ detector: { gap_tolerance_ms: v } });
+});
 
 agcToggle.addEventListener('change', () => queueSettingsUpdate({ agc: agcToggle.checked }));
 dcToggle.addEventListener('change', () => queueSettingsUpdate({ dc_block: dcToggle.checked }));
@@ -1175,16 +1229,27 @@ if (recDemodToggle) recDemodToggle.addEventListener('change', () => queueConfigU
 if (recDecodeToggle) recDecodeToggle.addEventListener('change', () => queueConfigUpdate({ recorder: { auto_decode: recDecodeToggle.checked } }));
 if (recMinSNR) recMinSNR.addEventListener('change', () => queueConfigUpdate({ recorder: { min_snr_db: parseFloat(recMinSNR.value) } }));
 if (recMaxDisk) recMaxDisk.addEventListener('change', () => queueConfigUpdate({ recorder: { max_disk_mb: parseInt(recMaxDisk.value || '0', 10) } }));
+if (recClassFilter) recClassFilter.addEventListener('change', () => {
+  const list = (recClassFilter.value || '')
+    .split(',')
+    .map(s => s.trim())
+    .filter(Boolean);
+  queueConfigUpdate({ recorder: { class_filter: list } });
+});
 
 avgSelect.addEventListener('change', () => {
   avgAlpha = parseFloat(avgSelect.value) || 0;
-  avgSpectrum = null;
+  resetProcessingCaches();
 });
 maxHoldToggle.addEventListener('change', () => {
   maxHold = maxHoldToggle.checked;
-  if (!maxHold) maxSpectrum = null;
+  maxSpectrum = null;
+  markSpectrumDirty();
+});
+resetMaxBtn.addEventListener('click', () => {
+  maxSpectrum = null;
+  markSpectrumDirty();
 });
-resetMaxBtn.addEventListener('click', () => { maxSpectrum = null; });
 followBtn.addEventListener('click', () => { followLive = true; pan = 0; });
 fitBtn.addEventListener('click', fitView);
 timelineFollowBtn.addEventListener('click', () => { timelineFrozen = false; });
@@ -1338,6 +1403,7 @@ window.addEventListener('keydown', (ev) => {
     maxHold = !maxHold;
     maxHoldToggle.checked = maxHold;
     if (!maxHold) maxSpectrum = null;
+    markSpectrumDirty();
   } else if (ev.key.toLowerCase() === 'g') {
     gpuToggle.checked = !gpuToggle.checked;
     queueConfigUpdate({ use_gpu_fft: gpuToggle.checked });
diff --git a/web/index.html b/web/index.html
index 13a2c32..024b8a1 100644
--- a/web/index.html
+++ b/web/index.html
@@ -355,6 +355,3 @@
   </script>
 </body>
 </html>
-t>
-</body>
-</html>