feat: CW decoder v2 — rebuilt decode engine, back in the UI

The first RX-audio CW decoder decoded poorly on real signals (vs SDC) and was
removed in cafade0. This rebuilds the DSP core from scratch in
internal/cwdecode, keeping v1's good ideas (pitch lock, Flex cw_pitch
targeting, tiered acquisition) and fixing its proven failures:

- Two-way DEBOUNCE (pending-commit ~0.3 dit): v1 rejected short marks but not
  short spaces, so a one-hop fade inside a dah shattered it into dits — the
  single worst real-signal failure.
- Per-character BATCH dit/dah classification at flush time, using the batch's
  own bimodal boundary — the first letter of an over decodes at any speed; the
  timing clusters (muDit/muDah) are updated with the same attribution, killing
  the classify-then-learn feedback spiral ("all dits at 60 WPM").
- dB-domain envelope with separate floor/peak trackers, hysteresis slicer,
  span CAP (30 dB — else quiet backgrounds put the off-threshold in the
  analysis-window skirts and letters merge) and window de-bias on durations.
- Double squelch: span >= 6 dB AND peak >= bank-median + 9.5 dB (span alone
  cannot reject pure noise).
- Hamming-windowed Goertzel, 16 ms window / 5 ms hop (a 20 ms window left
  40 WPM inter-element gaps with no envelope dip).
- Hardened acquisition (overlapping windows made "3 stable hops" meaningless)
  plus SUPERVISED RE-LOCK: a clearly stronger tone on another pitch sustained
  ~1 s takes over — heals noise locks and follows a QSY.
- Gap-fed dit-length tracking (inter-element gaps are timing evidence too).

Proven by a synthetic-signal test suite (all passing): clean 12-40 WPM, three
pitches, added noise, QSB fading 0.35-1.0, 10 ms dropouts inside dahs, QRM in
auto and targeted modes, noise-only squelch, mid-over speed change 25->15 WPM,
and jittered hand keying (+/-20-25%, 3 seeds).

Wiring and UI restored from git (app_cw.go, Ear header button, decoded-text
strip with WPM/pitch/level + pitch lock + click-a-word-to-fill-callsign, Tools
menu entry) — strip strings translated (cwd.* i18n keys, EN/FR) this time.

frontend/src/App.tsx

@@ -1,6 +1,6 @@
 import { useCallback, useEffect, useMemo, useRef, useState } from 'react';
 import {
-  Activity, AlertCircle, Antenna, Bell, CheckCircle2, Clock, CloudOff, Compass, Database, Eraser, Hash, Loader2, Lock,
+  Activity, AlertCircle, Antenna, Bell, CheckCircle2, Clock, CloudOff, Compass, Database, Ear, Eraser, Hash, Loader2, Lock,
   Maximize2, Minimize2, Mic, MessageSquare, Pencil, Radio, RadioTower, RefreshCw, Satellite, Send, Settings, SlidersHorizontal, Square, Terminal, Trash2, Unlock, X, Zap,
 } from 'lucide-react';
 
@@ -39,6 +39,7 @@ import {
   IcomSendCW, IcomStopCW, IcomSetKeySpeed, IcomSetBreakIn, GetIcomState,
   FlexSendCW, FlexStopCW, FlexSetKeySpeed, FlexBackspaceCW,
   GetDVKMessages, GetDVKStatus, DVKPlay, DVKStop,
+  StartCWDecoder, StopCWDecoder, SetCWDecoderPitch,
   ChatAvailable, GetChatHistory, SendChatMessage, GetOnlineOperators,
   QSOAudioBegin, QSOAudioCancel, QSOAudioRestart, QSOAudioResetClock,
   GetAwardDefs,
@@ -852,6 +853,37 @@ export default function App() {
 
   // === Digital Voice Keyer (DVK) ===
 
+  // CW decoder: taps RX audio and decodes Morse. Runs only when enabled AND the
+  // mode is CW. The decoded text appears in a strip above the tabs.
+  const [cwEnabled, setCwEnabled] = useState(() => localStorage.getItem('opslog.cwDecoder') === '1');
+  const [cwText, setCwText] = useState('');
+  const [cwStatus, setCwStatus] = useState<{ wpm: number; pitch: number; level: number; active: boolean }>({ wpm: 0, pitch: 0, level: 0, active: false });
+  const cwOn = cwEnabled && mode === 'CW';
+  // Keep the decoded line scrolled to the newest text (left-aligned, no scrollbar).
+  const cwScrollRef = useRef<HTMLDivElement>(null);
+  useEffect(() => { const el = cwScrollRef.current; if (el) el.scrollLeft = el.scrollWidth; }, [cwText]);
+  // Manual pitch override ('' = Auto: follow the radio's CW pitch / search).
+  const [cwPitch, setCwPitch] = useState(() => localStorage.getItem('opslog.cwPitch') || '');
+  useEffect(() => {
+    const hz = parseInt(cwPitch, 10);
+    SetCWDecoderPitch(Number.isFinite(hz) ? hz : 0).catch(() => {});
+    localStorage.setItem('opslog.cwPitch', cwPitch);
+  }, [cwPitch, cwOn]);
+  useEffect(() => {
+    const offT = EventsOn('cw:text', (txt: string) => setCwText((s) => (s + txt).slice(-200)));
+    const offS = EventsOn('cw:status', (st: any) => setCwStatus(st));
+    const offE = EventsOn('cw:error', (e: string) => { setError(String(e)); setCwEnabled(false); });
+    return () => { offT?.(); offS?.(); offE?.(); };
+  }, []);
+  // Start/stop the backend decoder as the (enabled, mode) combination changes.
+  useEffect(() => {
+    if (cwOn) { StartCWDecoder().catch((e: any) => { setError(String(e?.message ?? e)); setCwEnabled(false); }); }
+    else { StopCWDecoder().catch(() => {}); }
+  }, [cwOn]);
+  function toggleCwDecoder() {
+    setCwEnabled((v) => { const n = !v; localStorage.setItem('opslog.cwDecoder', n ? '1' : '0'); return n; });
+  }
+
   // === Multi-op chat (shared MySQL logbook) — docked panel like rotor/DVK ===
   const [chatAvailable, setChatAvailable] = useState(false);
   const [chatOpen, setChatOpen] = useState(false);
@@ -2908,6 +2940,7 @@ export default function App() {
       { type: 'separator' },
       { type: 'item', label: (wkEnabled ? '✓ ' : '') + t('tools.winkeyer'), action: 'tools.winkeyer' },
       { type: 'item', label: (dvkEnabled ? '✓ ' : '') + t('tools.dvk'), action: 'tools.dvk' },
+      { type: 'item', label: (cwEnabled ? '✓ ' : '') + t('tools.cwDecoder'), action: 'tools.cwdecoder' },
       { type: 'separator' },
       { type: 'item', label: (netEnabled ? '✓ ' : '') + t('tools.net'), action: 'tools.net' },
       { type: 'item', label: (contestTabEnabled ? '✓ ' : '') + t('tools.contest'), action: 'tools.contest' },
@@ -2930,7 +2963,7 @@ export default function App() {
       { type: 'separator' },
       { type: 'item', label: t('help.about'), action: 'help.about' },
     ]},
-  ], [total, selectedId, selectedIds, ctyRefreshing, refsDownloading, exporting, wkEnabled, dvkEnabled, netEnabled, contestTabEnabled, smtpConfigured, sendingLog, t]);
+  ], [total, selectedId, selectedIds, ctyRefreshing, refsDownloading, exporting, wkEnabled, dvkEnabled, cwEnabled, netEnabled, contestTabEnabled, smtpConfigured, sendingLog, t]);
 
   function handleMenu(action: string) {
     switch (action) {
@@ -2951,6 +2984,7 @@ export default function App() {
       case 'tools.qsldesigner': setQslDesignerOpen(true); break;
       case 'tools.winkeyer':    wkSetEnabled(!wkEnabled); break;
       case 'tools.dvk':         setDvkEnabled((v) => !v); break;
+      case 'tools.cwdecoder':   toggleCwDecoder(); break;
       case 'tools.net':         setNetEnabled((v) => { const nv = !v; if (nv) setActiveTab('net'); return nv; }); break;
       case 'tools.contest':     setContestTabEnabled((v) => { const nv = !v; if (nv) setActiveTab('contest'); else setActiveTab((tb) => (tb === 'contest' ? 'recent' : tb)); return nv; }); break;
       case 'tools.alerts':      setAlertsOpen(true); break;
@@ -4000,6 +4034,20 @@ export default function App() {
               <Zap className="size-4" />
               {wkStatus.busy && <span className="absolute -top-0.5 -right-0.5 size-2 rounded-full bg-warning animate-pulse" />}
             </button>
+            <button
+              type="button"
+              onClick={toggleCwDecoder}
+              title={cwEnabled ? (mode === 'CW' ? t('cwd.tipOnCw') : t('cwd.tipOnIdle')) : t('cwd.tipOff')}
+              className={cn(
+                'relative inline-flex items-center justify-center size-7 rounded-md border transition-colors',
+                cwOn && cwStatus.active ? 'border-success bg-success-muted text-success-muted-foreground'
+                  : cwEnabled ? 'border-success-border bg-success-muted text-success-muted-foreground hover:bg-success-muted'
+                  : 'border-border text-muted-foreground hover:bg-muted',
+              )}
+            >
+              <Ear className="size-4" />
+              {cwOn && cwStatus.active && <span className="absolute -top-0.5 -right-0.5 size-2 rounded-full bg-success animate-pulse" />}
+            </button>
             <button
               type="button"
               onClick={() => { const v = !showRotor; setShowRotor(v); writeUiPref('opslog.showRotor', v ? '1' : '0'); }}
@@ -4664,6 +4712,53 @@ export default function App() {
       </div>{/* /entry + aside row */}
 
       {/* ===== CW decoder strip (only when enabled AND mode is CW) ===== */}
+      {cwOn && (
+        <div className="ml-2.5 mt-1.5 -mb-1 w-[45%] flex items-center gap-2 rounded-md border border-success-border/70 bg-success-muted/60 px-2 py-1.5 text-xs">
+          <Ear className={cn('size-4 shrink-0', cwStatus.active ? 'text-success' : 'text-muted-foreground')} />
+          {/* Input-level meter — if this stays flat with a strong signal, the RX
+              audio device is wrong/silent rather than a decode problem. */}
+          <div className="shrink-0 w-12 h-1.5 rounded bg-muted overflow-hidden" title={t('cwd.levelTip', { pct: Math.round(cwStatus.level * 100) })}>
+            <div className="h-full bg-success transition-[width] duration-100" style={{ width: `${Math.min(100, Math.round(cwStatus.level * 100))}%` }} />
+          </div>
+          <span className="shrink-0 font-mono text-[10px] text-muted-foreground tabular-nums">
+            {cwStatus.wpm > 0 ? `${cwStatus.wpm} WPM` : '— WPM'} · {cwStatus.pitch > 0 ? `${cwStatus.pitch} Hz` : '— Hz'}
+          </span>
+          {/* Lock pitch: blank = Auto (follow the Flex CW pitch / search). */}
+          <input
+            type="number"
+            value={cwPitch}
+            onChange={(e) => setCwPitch(e.target.value)}
+            placeholder="auto"
+            title={t('cwd.pitchTip')}
+            className="shrink-0 w-14 h-5 rounded border border-success-border/70 bg-card/60 px-1 text-[10px] font-mono text-center outline-none"
+          />
+          {/* Left-aligned single line, no scrollbar; auto-scrolled to the newest
+              text (see cwScrollRef effect) so the latest stays in view. */}
+          <div ref={cwScrollRef} className="flex-1 min-w-0 overflow-hidden font-mono leading-none flex items-center">
+            {cwText.trim() === '' ? (
+              <span className="text-muted-foreground italic">{t('cwd.listening')}</span>
+            ) : (
+              <div className="inline-flex items-center whitespace-nowrap">
+                {cwText.trim().split(/\s+/).map((tok, i) => (
+                  <button
+                    key={i}
+                    type="button"
+                    className="mr-1 shrink-0 rounded px-1 leading-none hover:bg-success-muted/70"
+                    title={t('cwd.useCall')}
+                    onClick={() => onCallsignInput(tok, { force: true })}
+                  >
+                    {tok}
+                  </button>
+                ))}
+              </div>
+            )}
+          </div>
+          <button type="button" className="shrink-0 text-muted-foreground hover:text-foreground" title={t('cwd.clear')} onClick={() => setCwText('')}>
+            <Eraser className="size-3.5" />
+          </button>
+        </div>
+      )}
+
       {/* ===== LOWER: tabbed table / cluster / band map ===== */}
       {compact ? null : <>
       <div className={cn('grid gap-2.5 p-2.5 flex-1 min-h-0 grid-rows-[minmax(0,1fr)]',

frontend/src/lib/i18n.tsx

@@ -32,6 +32,12 @@ const en: Dict = {
   'view.refresh': 'Refresh', 'view.clearFilters': 'Clear filters',
   'tools.qslManager': 'QSL Manager…', 'tools.qslDesigner': 'QSL Card Designer…',
   'tools.winkeyer': 'WinKeyer CW keyer', 'tools.dvk': 'Digital Voice Keyer', 'tools.cwDecoder': 'CW decoder (RX audio)',
+  'cwd.listening': 'listening…', 'cwd.clear': 'Clear', 'cwd.useCall': 'Use as callsign',
+  'cwd.pitchTip': "Lock the decoder to this pitch (Hz). Blank = follow the radio's CW pitch / auto-search.",
+  'cwd.levelTip': 'Audio level {pct}%',
+  'cwd.tipOnCw': 'CW decoder — on (decoding) · click to disable',
+  'cwd.tipOnIdle': 'CW decoder — on, idle until CW mode · click to disable',
+  'cwd.tipOff': 'CW decoder · click to enable (decodes RX audio in CW mode)',
   'tools.net': 'NET Control', 'tools.alerts': 'Alert management…', 'tools.contest': 'Contest mode',
   'alert.tuneHint': 'Click to tune the rig to this spot (freq + mode) and fill the call', 'alert.dismiss': 'Dismiss', 'alert.pending': '{n} recent spot alert(s) — click to view', 'alert.noneShort': 'No recent alerts', 'alert.recent': 'Recent alerts', 'alert.clear': 'Clear',
   'menu.help': 'Help', 'help.about': 'About OpsLog', 'tools.duplicates': 'Find duplicates…',
@@ -366,6 +372,12 @@ const fr: Dict = {
   'view.refresh': 'Rafraîchir', 'view.clearFilters': 'Effacer les filtres',
   'tools.qslManager': 'Gestionnaire QSL…', 'tools.qslDesigner': 'Créateur de carte QSL…',
   'tools.winkeyer': 'Manipulateur CW WinKeyer', 'tools.dvk': 'Manipulateur vocal numérique', 'tools.cwDecoder': 'Décodeur CW (audio RX)',
+  'cwd.listening': 'écoute…', 'cwd.clear': 'Effacer', 'cwd.useCall': "Utiliser comme indicatif",
+  'cwd.pitchTip': "Verrouille le décodeur sur cette tonalité (Hz). Vide = suit le pitch CW de la radio / recherche auto.",
+  'cwd.levelTip': 'Niveau audio {pct}%',
+  'cwd.tipOnCw': 'Décodeur CW — actif (décode) · clic pour désactiver',
+  'cwd.tipOnIdle': 'Décodeur CW — actif, en veille hors mode CW · clic pour désactiver',
+  'cwd.tipOff': 'Décodeur CW · clic pour activer (décode l’audio RX en mode CW)',
   'tools.net': 'Contrôle de NET', 'tools.alerts': 'Gestion des alertes…', 'tools.contest': 'Mode contest',
   'alert.tuneHint': 'Cliquer pour accorder la radio sur ce spot (fréq + mode) et remplir l\'indicatif', 'alert.dismiss': 'Fermer', 'alert.pending': '{n} alerte(s) de spot récente(s) — cliquer pour voir', 'alert.noneShort': 'Aucune alerte récente', 'alert.recent': 'Alertes récentes', 'alert.clear': 'Effacer',
   'menu.help': 'Aide', 'help.about': 'À propos d\'OpsLog', 'tools.duplicates': 'Trouver les doublons…',

frontend/wailsjs/go/main/App.d.ts

@@ -86,6 +86,8 @@ export function BulkUpdateField(arg1:Array<number>,arg2:string,arg3:string):Prom
 
 export function BulkUpdateQSL(arg1:Array<number>,arg2:main.QSLBulkUpdate):Promise<number>;
 
+export function CWDecoderRunning():Promise<boolean>;
+
 export function ChatAvailable():Promise<boolean>;
 
 export function CheckForUpdate():Promise<main.UpdateInfo>;
@@ -368,6 +370,8 @@ export function GetCATSettings():Promise<main.CATSettings>;
 
 export function GetCATState():Promise<cat.RigState>;
 
+export function GetCWDecoderPitch():Promise<number>;
+
 export function GetCatalogCodes():Promise<Array<string>>;
 
 export function GetChangelog():Promise<Array<main.ChangelogEntry>>;
@@ -858,6 +862,8 @@ export function SetCATFrequency(arg1:number):Promise<void>;
 
 export function SetCATMode(arg1:string):Promise<void>;
 
+export function SetCWDecoderPitch(arg1:number):Promise<void>;
+
 export function SetClublogCtyEnabled(arg1:boolean):Promise<void>;
 
 export function SetClublogMostWantedEnabled(arg1:boolean):Promise<void>;
@@ -876,8 +882,12 @@ export function SetUIPref(arg1:string,arg2:string):Promise<void>;
 
 export function SetUltrabeamDirection(arg1:number):Promise<void>;
 
+export function StartCWDecoder():Promise<void>;
+
 export function StationSetRelay(arg1:string,arg2:number,arg3:boolean):Promise<void>;
 
+export function StopCWDecoder():Promise<void>;
+
 export function SwitchCATRig(arg1:number):Promise<void>;
 
 export function SyncPOTAHunterLog(arg1:boolean,arg2:boolean):Promise<main.POTASyncResult>;

frontend/wailsjs/go/main/App.js

@@ -126,6 +126,10 @@ export function BulkUpdateQSL(arg1, arg2) {
   return window['go']['main']['App']['BulkUpdateQSL'](arg1, arg2);
 }
 
+export function CWDecoderRunning() {
+  return window['go']['main']['App']['CWDecoderRunning']();
+}
+
 export function ChatAvailable() {
   return window['go']['main']['App']['ChatAvailable']();
 }
@@ -690,6 +694,10 @@ export function GetCATState() {
   return window['go']['main']['App']['GetCATState']();
 }
 
+export function GetCWDecoderPitch() {
+  return window['go']['main']['App']['GetCWDecoderPitch']();
+}
+
 export function GetCatalogCodes() {
   return window['go']['main']['App']['GetCatalogCodes']();
 }
@@ -1670,6 +1678,10 @@ export function SetCATMode(arg1) {
   return window['go']['main']['App']['SetCATMode'](arg1);
 }
 
+export function SetCWDecoderPitch(arg1) {
+  return window['go']['main']['App']['SetCWDecoderPitch'](arg1);
+}
+
 export function SetClublogCtyEnabled(arg1) {
   return window['go']['main']['App']['SetClublogCtyEnabled'](arg1);
 }
@@ -1706,10 +1718,18 @@ export function SetUltrabeamDirection(arg1) {
   return window['go']['main']['App']['SetUltrabeamDirection'](arg1);
 }
 
+export function StartCWDecoder() {
+  return window['go']['main']['App']['StartCWDecoder']();
+}
+
 export function StationSetRelay(arg1, arg2, arg3) {
   return window['go']['main']['App']['StationSetRelay'](arg1, arg2, arg3);
 }
 
+export function StopCWDecoder() {
+  return window['go']['main']['App']['StopCWDecoder']();
+}
+
 export function SwitchCATRig(arg1) {
   return window['go']['main']['App']['SwitchCATRig'](arg1);
 }