fix: pre-roll metronome ticks are missing

src/core/audio-interface/KGMetronome.test.ts

@@ -0,0 +1,57 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+import { MockLoop, MockTransport, ToneMock } from '../../test/mocks/tone'
+
+vi.mock('tone', async () => {
+  const { ToneMock: toneMock } = await import('../../test/mocks/tone')
+  return toneMock
+})
+
+import { KGMetronome } from './KGMetronome'
+
+describe('KGMetronome', () => {
+  beforeEach(() => {
+    vi.useFakeTimers()
+    vi.clearAllMocks()
+    MockTransport.bpm.value = 120
+    MockTransport.getTicksAtTime.mockImplementation((time: number) => time * MockTransport.PPQ)
+    vi.mocked(ToneMock.now).mockReturnValue(42)
+  })
+
+  it('schedules audible preroll clicks before beat 0 and keeps the beat 0 accent', () => {
+    const metronome = new KGMetronome()
+    const triggerAttackRelease = vi.fn()
+    ;(metronome as unknown as { sampler: unknown }).sampler = {
+      loaded: true,
+      triggerAttackRelease,
+    }
+
+    metronome.start(-4, 4, 0.2)
+
+    vi.advanceTimersByTime(200)
+    expect(triggerAttackRelease).toHaveBeenNthCalledWith(1, 'C5', '16n', 42)
+
+    vi.advanceTimersByTime(1000)
+    expect(triggerAttackRelease).toHaveBeenNthCalledWith(2, 'C4', '16n', 42)
+
+    const transportLoop = MockLoop.mock.results[0]?.value
+    expect(transportLoop).toBeDefined()
+
+    transportLoop.callback(0)
+    expect(triggerAttackRelease).toHaveBeenLastCalledWith('C5', '16n', 0.2)
+  })
+
+  it('cancels pending preroll clicks when stopped', () => {
+    const metronome = new KGMetronome()
+    const triggerAttackRelease = vi.fn()
+    ;(metronome as unknown as { sampler: unknown }).sampler = {
+      loaded: true,
+      triggerAttackRelease,
+    }
+
+    metronome.start(-2, 4, 0.2)
+    metronome.stop()
+    vi.runAllTimers()
+
+    expect(triggerAttackRelease).not.toHaveBeenCalled()
+  })
+})