Ambient WebGL petals + cute notification sounds

Add a fixed, GPU-driven petal layer that drifts soft blossoms over the
page (sparse, translucent, paused when hidden, skipped under
prefers-reduced-motion). Add a synthesized cute sound palette — bubble
pop, water droplet, soft bell, sparkle, cheer — generated as embedded
WAV assets (scripts/gen_sounds.py) and played through a quiet Web Audio
bus with soft-clipping and a persisted mute toggle in the status bar.

Sounds fire per suggestion type when fresh advice arrives (staggered,
old pending advice stays silent) and on companion bubbles by tone.

Claude-Session: https://claude.ai/code/session_016Yr6jELuRc7hyzYLccQKZd

web/src/audio/sounds.ts

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+// Petal's cute sound palette. The actual tones live as tiny WAV assets in
+// ./assets (generated by scripts/gen_sounds.py — warm bubble pops, water drops,
+// and soft bells tuned to match the app's gentle look). Vite fingerprints and
+// bundles them into dist, so they ride along inside the single Go binary; here
+// we just fetch + decode them once and play them through a Web Audio bus with a
+// soft master volume. The whole thing is opt-out-able and the mute choice
+// persists in localStorage so it survives reloads.
+
+import popUrl from '../assets/sounds/pop.wav'
+import dropletUrl from '../assets/sounds/droplet.wav'
+import chimeUrl from '../assets/sounds/chime.wav'
+import shimmerUrl from '../assets/sounds/shimmer.wav'
+import cheerUrl from '../assets/sounds/cheer.wav'
+
+const STORAGE_KEY = 'petal.sound'
+
+// Master volume — deliberately gentle. These are background delights, not alerts.
+const MASTER_GAIN = 0.5
+
+export type SoundName =
+  | 'pop' // a soft bubble pop — the signature "something arrived"
+  | 'droplet' // a single rounded water-drop ping
+  | 'chime' // a gentle two-note bell
+  | 'shimmer' // three quick ascending sparkles
+  | 'cheer' // a happy little major arpeggio (accepts, milestones)
+
+const SOURCES: Record<SoundName, string> = {
+  pop: popUrl,
+  droplet: dropletUrl,
+  chime: chimeUrl,
+  shimmer: shimmerUrl,
+  cheer: cheerUrl,
+}
+
+let ctx: AudioContext | null = null
+let master: GainNode | null = null
+const buffers = new Map<SoundName, AudioBuffer>()
+let enabled = readEnabled()
+const listeners = new Set<(on: boolean) => void>()
+
+function readEnabled(): boolean {
+  try {
+    return localStorage.getItem(STORAGE_KEY) !== 'off'
+  } catch {
+    return true
+  }
+}
+
+export function isSoundEnabled(): boolean {
+  return enabled
+}
+
+export function setSoundEnabled(on: boolean): void {
+  enabled = on
+  try {
+    localStorage.setItem(STORAGE_KEY, on ? 'on' : 'off')
+  } catch {
+    /* private mode — choice just won't persist */
+  }
+  listeners.forEach((fn) => fn(on))
+  // Touching the context on enable doubles as a user-gesture unlock + warm-up.
+  if (on) void ensureContext()
+}
+
+export function onSoundEnabledChange(fn: (on: boolean) => void): () => void {
+  listeners.add(fn)
+  return () => listeners.delete(fn)
+}
+
+// Lazily create the AudioContext (browsers require a user gesture before audio
+// can play; the first play() after a click will succeed, earlier ones resume).
+async function ensureContext(): Promise<AudioContext | null> {
+  if (typeof window === 'undefined') return null
+  const AC: typeof AudioContext | undefined =
+    window.AudioContext ??
+    (window as unknown as { webkitAudioContext?: typeof AudioContext }).webkitAudioContext
+  if (!AC) return null
+  if (!ctx) {
+    ctx = new AC()
+    master = ctx.createGain()
+    master.gain.value = MASTER_GAIN
+    // A gentle soft-clip so stacked sounds never crackle.
+    const shaper = ctx.createWaveShaper()
+    shaper.curve = softClipCurve()
+    master.connect(shaper)
+    shaper.connect(ctx.destination)
+  }
+  if (ctx.state === 'suspended') {
+    try {
+      await ctx.resume()
+    } catch {
+      /* will retry on the next gesture */
+    }
+  }
+  return ctx
+}
+
+function softClipCurve(): Float32Array<ArrayBuffer> {
+  const n = 1024
+  const curve = new Float32Array(new ArrayBuffer(n * 4))
+  for (let i = 0; i < n; i++) {
+    const x = (i / (n - 1)) * 2 - 1
+    curve[i] = Math.tanh(x * 1.2)
+  }
+  return curve
+}
+
+// Fetch + decode one sound, caching the decoded buffer for instant replay.
+async function load(name: SoundName, audio: AudioContext): Promise<AudioBuffer | null> {
+  const cached = buffers.get(name)
+  if (cached) return cached
+  try {
+    const res = await fetch(SOURCES[name])
+    const bytes = await res.arrayBuffer()
+    const buf = await audio.decodeAudioData(bytes)
+    buffers.set(name, buf)
+    return buf
+  } catch {
+    return null // asset missing / decode failed — sound just won't play
+  }
+}
+
+// Warm the cache so the first real play is instant.
+async function prime(): Promise<void> {
+  const audio = await ensureContext()
+  if (!audio) return
+  await Promise.all((Object.keys(SOURCES) as SoundName[]).map((n) => load(n, audio)))
+}
+
+// Fire a sound. No-op when muted or audio is unavailable. Never throws — a
+// delight that fails should fail silently.
+export function playSound(name: SoundName): void {
+  if (!enabled) return
+  void (async () => {
+    const audio = await ensureContext()
+    if (!audio || !master || audio.state !== 'running') return
+    const buf = await load(name, audio)
+    if (!buf) return
+    try {
+      const src = audio.createBufferSource()
+      src.buffer = buf
+      src.connect(master)
+      src.start()
+    } catch {
+      /* audio glitch — ignore */
+    }
+  })()
+}
+
+// Map an editor suggestion type to its sound, so each kind of help has its own
+// little voice (grammar pops like a bubble, idioms chime, etc.).
+const SUGGESTION_SOUND: Record<string, SoundName> = {
+  grammar: 'pop',
+  phrasing: 'droplet',
+  idiom: 'chime',
+  clarity: 'shimmer',
+  voice: 'droplet',
+}
+
+export function playSuggestionSound(type: string): void {
+  playSound(SUGGESTION_SOUND[type] ?? 'pop')
+}
+
+// Unlock + warm audio on the first user gesture so the very first sound isn't
+// dropped by the browser's autoplay policy. Self-removing.
+if (typeof window !== 'undefined') {
+  const unlock = () => {
+    void prime()
+    window.removeEventListener('pointerdown', unlock)
+    window.removeEventListener('keydown', unlock)
+  }
+  window.addEventListener('pointerdown', unlock)
+  window.addEventListener('keydown', unlock)
+}