Add Assist mode: primitive note display for practicing from paper

New game mode 'assist' — no trainer, no scoring:
- Large display of the currently mic-detected note
- Live notation staff (same pipeline as the pitch monitor)
- Live fretboard showing alternative positions for the played note
  (respects the fret-window practice filter)
- Tuner and Metronome remain the shared footer tools, identical in
  all modes; user can practice own-pace from paper with a free
  metronome

Header mode toggle gains 'Assist'; 'm' shortcut cycles back to sight
reading from assist/phrase. Export PitchData type.

src/App.css

@@ -1126,3 +1126,49 @@ button {
     justify-content: safe center;
     justify-content: center;
 }
+
+/* ---- Assist Mode ------------------------------------------------------- */
+/* Primitive practice companion: big detected note + live staff + optional
+   fretboard with alternative positions. No trainer actions. */
+
+.assist-card {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: var(--spacing-md);
+  padding: var(--spacing-lg);
+}
+
+.assist-note-area {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  min-height: 110px;
+}
+
+.assist-note-name {
+  font-size: 5rem;
+  font-weight: 800;
+  line-height: 1;
+  color: var(--color-text-main);
+  font-variant-emoji: text;
+}
+
+.assist-note-name.placeholder {
+  color: var(--color-text-muted);
+  opacity: 0.5;
+}
+
+.assist-fretboard {
+  width: 100%;
+  display: flex;
+  justify-content: center;
+  overflow-x: auto;
+}
+
+.assist-hint {
+  font-size: 12px;
+  color: var(--color-text-muted);
+  margin: 0;
+  text-align: center;
+}

src/App.tsx

@@ -8,6 +8,7 @@ import { SingleNoteTrainer, type SingleNoteHandle } from './components/SingleNot
 import { LiveNoteStaff } from './components/LiveNoteStaff';
 import { resolveClefTranspose } from './music/InstrumentConfigs';
 import { PhraseTrainer, type PhraseHandle } from './components/PhraseTrainer';
+import { AssistMode } from './components/AssistMode';
 import { usePitchDetector } from './hooks/usePitchDetector';
 import { useSettings } from './context/useSettings';
 import { audioEngine } from './audio/AudioEngine';
@@ -26,6 +27,7 @@ function App() {
   const setSettings = updateSettings;
 
   const isPhrase = settings.gameMode === 'phrase';
+  const isAssist = settings.gameMode === 'assist';
 
   const currentTuning = TUNINGS[settings.tuningId];
   const currentInstrumentDef = INSTRUMENT_DEFINITIONS[settings.instrument];
@@ -175,6 +177,25 @@ function App() {
         return;
       }
 
+      if (isAssist) {
+        // Assist mode: only display shortcuts — no trainer actions.
+        switch (e.key.toLowerCase()) {
+          case 'h':
+            setSettings(s => ({ ...s, showHint: !s.showHint }));
+            break;
+          case 'z':
+            setSettings(s => ({ ...s, zenMode: !s.zenMode }));
+            break;
+          case 'v':
+            setSettings(s => ({ ...s, showFretboard: !s.showFretboard }));
+            break;
+          case 'l':
+            setListening(l => !l);
+            break;
+        }
+        return;
+      }
+
       switch (e.key.toLowerCase()) {
         case 'h':
           setSettings(s => ({ ...s, showHint: !s.showHint }));
@@ -207,16 +228,16 @@ function App() {
 
     window.addEventListener('keydown', handleKeyDown);
     return () => window.removeEventListener('keydown', handleKeyDown);
-  }, [settings, showHelp, isPhrase, setSettings]);
+  }, [settings, showHelp, isPhrase, isAssist, setSettings]);
 
-  // 'm' cycles all three modes from phrase mode too.
+  // 'm' cycles back to sight reading from phrase/assist modes.
   useEffect(() => {
     const handler = (e: KeyboardEvent) => {
       if (e.key.toLowerCase() !== 'm') return;
       const target = e.target as HTMLElement | null;
       if (target instanceof HTMLInputElement || target instanceof HTMLTextAreaElement ||
         target instanceof HTMLButtonElement || target instanceof HTMLSelectElement || target?.isContentEditable) return;
-      if (settings.gameMode === 'phrase') {
+      if (settings.gameMode === 'phrase' || settings.gameMode === 'assist') {
         setSettings(s => ({ ...s, gameMode: 'sight_reading' }));
       }
     };
@@ -263,6 +284,13 @@ function App() {
               >
                 Phrases
               </button>
+              <button
+                className={`toggle-option ${settings.gameMode === 'assist' ? 'active' : ''}`}
+                onClick={() => setSettings(s => ({ ...s, gameMode: 'assist' }))}
+                title="Practice companion: shows played notes while you work from paper"
+              >
+                Assist
+              </button>
             </div>
 
             <button
@@ -305,6 +333,11 @@ function App() {
             micError={error}
             windowWidth={windowWidth}
           />
+        ) : isAssist ? (
+          <AssistMode
+            pitchData={displayedPitch}
+            windowWidth={windowWidth}
+          />
         ) : (
           <SingleNoteTrainer
             ref={singleNoteRef}

src/components/AssistMode.tsx

@@ -0,0 +1,89 @@
+/**
+ * Assist Mode — primitive practice companion for working from paper.
+ *
+ * No trainer, no scoring: shows the currently played (mic-detected) note
+ * large, optionally with a live fretboard of alternative positions for that
+ * note. Tuner and Metronome come from the shared footer tools (Controls),
+ * so they stay identical across all modes.
+ */
+import { INSTRUMENT_DEFINITIONS, resolveClefTranspose } from '../music/InstrumentConfigs';
+import { useMemo } from 'react';
+import { useSettings } from '../context/useSettings';
+import { TUNINGS, getFretboardPositions } from '../music/Tunings';
+import { isFrettedInstrument } from '../music/playableRange';
+import { getPracticeFilter } from '../types/SettingsTypes';
+import { Fretboard } from './Fretboard';
+import { LiveNoteStaff } from './LiveNoteStaff';
+import type { PitchData } from '../hooks/usePitchDetector';
+
+interface AssistModeProps {
+    pitchData: PitchData | null;
+    /** True while the app's own audio is audible (mic gate) — caller decides. */
+    windowWidth: number;
+}
+
+export const AssistMode: React.FC<AssistModeProps> = ({ pitchData, windowWidth }) => {
+    const { settings } = useSettings();
+    const currentTuning = TUNINGS[settings.tuningId];
+    const currentInstrumentDef = INSTRUMENT_DEFINITIONS[settings.instrument];
+
+    const fretted = isFrettedInstrument(settings.instrument) && !!currentTuning;
+    const pf = getPracticeFilter(settings);
+
+    // Alternative positions for the detected note (respect fret window filter)
+    const positions = useMemo(() => {
+        if (!fretted || !currentTuning || !pitchData) return [];
+        const all = getFretboardPositions(pitchData.midi, currentTuning, 20);
+        if (!pf.fretWindowEnabled) return all;
+        return all.filter(p => p.fret >= Math.max(0, pf.fretMin) && p.fret <= Math.min(24, pf.fretMax));
+    }, [fretted, currentTuning, pitchData, pf.fretWindowEnabled, pf.fretMin, pf.fretMax]);
+
+    const { clef, transpose } = useMemo(() =>
+        resolveClefTranspose(currentInstrumentDef, settings.difficulty),
+    [currentInstrumentDef, settings.difficulty]);
+
+    const staffWidth = Math.min(windowWidth - 40, 860);
+
+    return (
+        <div className="card sheet-music-card assist-card">
+            <div className="assist-note-area">
+                {pitchData ? (
+                    <span className="assist-note-name">{pitchData.note}</span>
+                ) : (
+                    <span className="assist-note-name placeholder">—</span>
+                )}
+            </div>
+
+            <div className="sheet-music-container">
+                <LiveNoteStaff
+                    midi={pitchData ? pitchData.midi : null}
+                    transpose={transpose}
+                    keySignature={settings.keySignature}
+                    clef={clef === 'grand' ? undefined : clef}
+                    width={Math.min(240, staffWidth)}
+                    theme={settings.theme}
+                />
+            </div>
+
+            {fretted && currentTuning && (
+                <div className="assist-fretboard">
+                    <Fretboard
+                        tuning={currentTuning}
+                        positions={positions}
+                        maxFrets={15}
+                        showHints={false}
+                        interactive={false}
+                        displayTranspose={transpose}
+                    />
+                </div>
+            )}
+
+            {!pitchData && (
+                <p className="assist-hint">
+                    Play a note — it shows here. Mic is{' '}
+                    {settings.showTuningMeter ? 'on' : 'controlled by the mic button below'}.
+                </p>
+            )}
+        </div>
+    );
+};

src/hooks/usePitchDetector.ts

@@ -9,7 +9,7 @@ import {
     NOTE_DISPLAY_STABLE_FRAMES,
 } from '../AppConfig';
 
-interface PitchData {
+export interface PitchData {
     frequency: number;
     midi: number;
     note: string;

src/types/SettingsTypes.ts

@@ -134,7 +134,7 @@ export interface AppSettings {
     instrument: string;
     rhythm: RhythmSettings;
     zenMode: boolean;
-    gameMode: 'sight_reading' | 'ear_training' | 'phrase';
+    gameMode: 'sight_reading' | 'ear_training' | 'phrase' | 'assist';
     customMinFret?: number;
     customMaxFret?: number;
     autoPlaySightReading?: boolean;