fix(audio): correct re-play-after-stop bug, strengthen tests

Use pendingCancel flag (consumed once) to suppress stop-before-play while
allowing subsequent play() calls to proceed normally. Add afterEach timer
cleanup, re-play test, and behavioral assertion for off().

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/src/lib/audio.test.ts

@@ -1,4 +1,4 @@
-import { describe, it, expect, vi, beforeEach } from 'vitest'
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest'
 import { MorseAudioEngine } from './audio'
 
 describe('MorseAudioEngine', () => {
@@ -9,6 +9,10 @@ describe('MorseAudioEngine', () => {
     vi.useFakeTimers()
   })
 
+  afterEach(() => {
+    vi.useRealTimers()
+  })
+
   it('emits signal-start and signal-end events when playing E (.)', async () => {
     const starts: string[] = []
     const ends: string[] = []
@@ -34,7 +38,7 @@ describe('MorseAudioEngine', () => {
     expect(ended).toBe(true)
   })
 
-  it('stop() prevents further signals', async () => {
+  it('stop() before play() prevents signal emission', async () => {
     const starts: string[] = []
     engine.on('signal-start', ({ type }: { type: string }) => starts.push(type))
 
@@ -46,10 +50,31 @@ describe('MorseAudioEngine', () => {
     expect(starts).toHaveLength(0)
   })
 
-  it('can register and remove event listeners', () => {
+  it('play() works normally after a stop-before-play suppression', async () => {
+    const starts: string[] = []
+
+    // First play is suppressed
+    engine.stop()
+    await engine.play('SOS', 10)
+
+    // Second play should proceed normally
+    engine.on('signal-start', ({ type }: { type: string }) => starts.push(type))
+    const playPromise = engine.play('E', 10)
+    await vi.runAllTimersAsync()
+    await playPromise
+
+    expect(starts).toEqual(['dot'])
+  })
+
+  it('off() removes listener so it is not called', async () => {
     const cb = vi.fn()
     engine.on('play-end', cb)
     engine.off('play-end', cb)
-    // No assertion needed — just verify no errors thrown
+
+    const playPromise = engine.play('E', 10)
+    await vi.runAllTimersAsync()
+    await playPromise
+
+    expect(cb).not.toHaveBeenCalled()
   })
 })

client/src/lib/audio.ts

@@ -7,11 +7,11 @@ type AudioEventPayload = { type: SignalType } | undefined
 export class MorseAudioEngine {
   private ctx: AudioContext | null = null
   private listeners = new Map<AudioEventName, Array<(data?: AudioEventPayload) => void>>()
-  // Monotonically increasing. stop() increments it. play() records its value
-  // at the moment it clears the stopped state. A play session is valid only
-  // while activePlayId === stopGeneration (i.e. no new stop() has been called).
+  // stop() increments stopGeneration. play() captures it to detect mid-play cancellation.
   private stopGeneration = 0
-  private activePlayId = 0
+  // If stop() is called while no play is active, suppress exactly one upcoming play() call.
+  private pendingCancel = false
+  private isPlaying = false
 
   private getCtx(): AudioContext {
     if (!this.ctx || this.ctx.state === 'closed') {
@@ -33,25 +33,28 @@ export class MorseAudioEngine {
   }
 
   stop(): void {
+    // Only suppress the next play() if nothing is currently playing.
+    // If a play is in progress, stopGeneration increment is enough to cancel it.
+    if (!this.isPlaying) {
+      this.pendingCancel = true
+    }
     this.stopGeneration++
     this.ctx?.suspend()
   }
 
   async play(text: string, wpm = 10): Promise<void> {
-    // To allow playback, we align activePlayId with stopGeneration.
-    // But only do this if stop() was NOT called before this play() invocation.
-    // We detect "stop-before-play" by checking if stopGeneration > activePlayId
-    // (meaning stop was called more recently than the last play start).
-    // If so, we do NOT reset, so isStopped() remains true throughout.
-    const wasStoppedBeforePlay = this.stopGeneration > this.activePlayId
-    if (!wasStoppedBeforePlay) {
-      // Normal: no prior unmatched stop — activate this play session
-      this.activePlayId = this.stopGeneration
+    // Consume a pending pre-play cancellation (stop() was called before this play()).
+    // After consuming, the flag is clear so subsequent play() calls proceed normally.
+    if (this.pendingCancel) {
+      this.pendingCancel = false
+      return
     }
 
-    const myPlayId = this.activePlayId
-    const isStopped = () => this.stopGeneration !== myPlayId
+    this.isPlaying = true
+    const myGen = this.stopGeneration
+    const isStopped = () => this.stopGeneration !== myGen
 
+    try {
       const ctx = this.getCtx()
       if (ctx.state === 'suspended') await ctx.resume()
 
@@ -111,5 +114,8 @@ export class MorseAudioEngine {
 
       await new Promise<void>(resolve => setTimeout(resolve, totalMs))
       if (!isStopped()) this.emit('play-end')
+    } finally {
+      this.isPlaying = false
+    }
   }
 }