Arpeggio material for Phrase Mode (variant 1)

- music/arpeggioGenerator.ts: diatonic triads (I-vii*) built from the
  selected key/mode via the shared degree spelling; patterns up / down /
  up-down / 1-2-3-5; one or two octaves (cycle ends on the octave; two-
  octave path continues from the turning root). Quarter-note rhythm with
  final note extended to fill the bar; title is labeled 'Arpeggio -
  <tonic> <degree> (pattern, coverage)'.
- Settings: PhraseMaterial 'arpeggio' + arpeggioDegree/Pattern/Coverage
  (defaults I / up / one-octave).
- PhraseTrainer: material option 'Arpeggios (generated)' + Chord/Pattern/
  Coverage/Meter selects; key/mode reuse the shared Target key controls.
- Tests: 9 arpeggio cases (170 total).

src/music/arpeggioGenerator.test.ts

@@ -0,0 +1,91 @@
+import { describe, it, expect } from 'vitest';
+import { generateArpeggio } from './arpeggioGenerator';
+import { scoreEvents, validateScore } from '../score/model';
+
+const strings = [40, 45, 50, 55, 59, 64];
+const pool: number[] = [];
+for (const open of strings) for (let f = 0; f <= 12; f++) pool.push(open + f);
+
+const base = {
+    keyTonic: 'C',
+    keyMode: 'major' as const,
+    meter: { numerator: 4 as const, denominator: 4 as const },
+};
+
+describe('generateArpeggio', () => {
+    it('builds a C major arpeggio (up, one octave) from the pool', () => {
+        const r = generateArpeggio({ ...base, degree: 'I', pattern: 'up', coverage: 'one-octave' }, pool);
+        expect(r.ok).toBe(true);
+        if (!r.ok) return;
+        const ev = scoreEvents(r.value);
+        // C-E-G-C: 4 notes, quarter each (plus final extension)
+        const midis = ev.map(e => e.pitch!.midi);
+        expect(midis).toEqual([48, 52, 55, 60]);
+        expect(validateScore(r.value)).toEqual([]);
+        expect(r.value.title).toContain('Arpeggio');
+        expect(r.value.title).toContain('C I');
+    });
+
+    it('down pattern reverses the ascending cycle', () => {
+        const r = generateArpeggio({ ...base, degree: 'I', pattern: 'down', coverage: 'one-octave' }, pool);
+        expect(r.ok).toBe(true);
+        if (!r.ok) return;
+        const midis = scoreEvents(r.value).map(e => e.pitch!.midi);
+        expect(midis).toEqual([60, 55, 52, 48]);
+    });
+
+    it('updown returns to the starting root without duplicating the top', () => {
+        const r = generateArpeggio({ ...base, degree: 'I', pattern: 'updown', coverage: 'one-octave' }, pool);
+        expect(r.ok).toBe(true);
+        if (!r.ok) return;
+        const midis = scoreEvents(r.value).map(e => e.pitch!.midi);
+        // ascend C-E-G-C then descend back to C; only one C5 (turning point)
+        expect(midis).toEqual([48, 52, 55, 60, 55, 52, 48]);
+        expect(midis.filter(m => m === 60)).toHaveLength(1);
+    });
+
+    it('1235 pattern ends on the octave of the root', () => {
+        const r = generateArpeggio({ ...base, degree: 'I', pattern: '1235', coverage: 'one-octave' }, pool);
+        expect(r.ok).toBe(true);
+        if (!r.ok) return;
+        const midis = scoreEvents(r.value).map(e => e.pitch!.midi);
+        expect(midis).toEqual([48, 52, 55, 60]);
+    });
+
+    it('two-octave coverage spans 12 semitones beyond the first cycle', () => {
+        const r = generateArpeggio({ ...base, degree: 'I', pattern: 'up', coverage: 'two-octave' }, pool);
+        expect(r.ok).toBe(true);
+        if (!r.ok) return;
+        const midis = scoreEvents(r.value).map(e => e.pitch!.midi);
+        expect(midis).toEqual([48, 52, 55, 60, 64, 67, 72]);
+    });
+    it('spells the dominant triad G-B-D in C major', () => {
+        const r = generateArpeggio({ ...base, degree: 'V', pattern: 'up', coverage: 'one-octave' }, pool);
+        expect(r.ok).toBe(true);
+        if (!r.ok) return;
+        const pcs = scoreEvents(r.value).map(e => e.pitch!.midi % 12);
+        expect(pcs).toEqual([7, 11, 2, 7]); // G B D G
+    });
+
+    it('spells the leading-tone dim triad B-D-F in C major', () => {
+        const r = generateArpeggio({ ...base, degree: 'vii0', pattern: 'up', coverage: 'one-octave' }, pool);
+        expect(r.ok).toBe(true);
+        if (!r.ok) return;
+        const pcs = scoreEvents(r.value).map(e => e.pitch!.midi % 12);
+        expect(pcs).toEqual([11, 2, 5, 11]); // B D F B
+    });
+
+    it('fails cleanly when the pool cannot fit a full triad cycle', () => {
+        // Only frets 0-1 on all strings: no complete C-E-G cycle with octave
+        const tiny: number[] = [];
+        for (const open of strings) for (let f = 0; f <= 1; f++) tiny.push(open + f);
+        const r = generateArpeggio({ ...base, degree: 'I', pattern: 'up', coverage: 'one-octave' }, tiny);
+        expect(r.ok).toBe(false);
+    });
+
+    it('is deterministic for identical configs', () => {
+        const a = generateArpeggio({ ...base, degree: 'IV', pattern: 'updown', coverage: 'one-octave' }, pool);
+        const b = generateArpeggio({ ...base, degree: 'IV', pattern: 'updown', coverage: 'one-octave' }, pool);
+        expect(a).toEqual(b);
+    });
+});