Notification sounds: hand-picked mp3 palette + error/milestone cues

Replace the synthesized WAV blips with curated mp3 effects:
- error ("haiya") plays on LLM-down/timeout and save failures, debounced
  and on-transition-only, with a reassuring bilingual bubble
- milestone (Chinese fanfare) now fires every 100 words
- all other notifications draw from a rotating pop pool that never repeats
  the last sound, so batches of suggestions/tips stay lively

playPop() replaces the per-suggestion-type sound map; thread llmDown through
PetalCompanion -> useCompanion for the error cue. Old synth WAVs removed.

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

web/src/audio/sounds.ts

@@ -1,16 +1,18 @@
-// 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.
+// Petal's cute sound palette. These are hand-picked mp3 effects (warm bubble
+// pops, a wooden "tok", rolling baoding balls, a Chinese fanfare for milestones,
+// and a playful "haiya" for errors) living as assets in ./assets/sounds. 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'
+import pop1Url from '../assets/sounds/pop1.mp3'
+import pop2Url from '../assets/sounds/pop2.mp3'
+import tokUrl from '../assets/sounds/tok.mp3'
+import blockUrl from '../assets/sounds/block.mp3'
+import baodingUrl from '../assets/sounds/baoding.mp3'
+import milestoneUrl from '../assets/sounds/milestone.mp3'
+import errorUrl from '../assets/sounds/error.mp3'
 
 const STORAGE_KEY = 'petal.sound'
 
@@ -18,20 +20,32 @@ const STORAGE_KEY = 'petal.sound'
 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)
+  | 'pop1' // a soft bubble pop
+  | 'pop2' // a second bubble pop, slightly different
+  | 'tok' // a light wooden "tok"
+  | 'block' // a quick Chinese wood-block tap
+  | 'baoding' // rolling baoding-ball shimmer
+  | 'milestone' // a happy Chinese fanfare (word-count milestones)
+  | 'error' // a playful "haiya" — something went wrong
 
 const SOURCES: Record<SoundName, string> = {
-  pop: popUrl,
-  droplet: dropletUrl,
-  chime: chimeUrl,
-  shimmer: shimmerUrl,
-  cheer: cheerUrl,
+  pop1: pop1Url,
+  pop2: pop2Url,
+  tok: tokUrl,
+  block: blockUrl,
+  baoding: baodingUrl,
+  milestone: milestoneUrl,
+  error: errorUrl,
 }
 
+// The pool of light "something happened" notification sounds. We rotate through
+// these (skipping the one just played) so the same blip never repeats back to
+// back — a batch of suggestions or a run of tips stays lively instead of
+// hammering one note. milestone/error are deliberately NOT in the pool: they're
+// reserved for their specific moments.
+const POP_POOL: SoundName[] = ['pop1', 'pop2', 'tok', 'block', 'baoding']
+let lastPop = -1
+
 let ctx: AudioContext | null = null
 let master: GainNode | null = null
 const buffers = new Map<SoundName, AudioBuffer>()
@@ -147,18 +161,24 @@ export function playSound(name: SoundName): void {
   })()
 }
 
-// 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',
+// Play the next notification pop from the pool, never repeating the last one, so
+// consecutive blips always sound different. This is the everyday "something
+// arrived" voice for suggestions, tips, and gentle cheers.
+export function playPop(): void {
+  let i = lastPop
+  // Tiny pool, so a short scan to pick anything but the last is plenty.
+  for (let tries = 0; tries < POP_POOL.length && i === lastPop; tries++) {
+    i = Math.floor(Math.random() * POP_POOL.length)
+  }
+  lastPop = i
+  playSound(POP_POOL[i])
 }
 
-export function playSuggestionSound(type: string): void {
-  playSound(SUGGESTION_SOUND[type] ?? 'pop')
+// Each freshly-surfaced suggestion just gets a rotating pop — the variety comes
+// from the pool, not from the suggestion type, so a batch of same-type fixes
+// still sounds lively.
+export function playSuggestionSound(_type: string): void {
+  playPop()
 }
 
 // Unlock + warm audio on the first user gesture so the very first sound isn't