Add typewriter clatter during text reveal

A dry synthesized key-clack (filtered noise burst with pitch jitter) plays as
each line types out — every other non-space character — for a detective-terminal
feel. Skipped in the editor preview and when reduced-motion is set.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/audio.ts

@@ -10,6 +10,17 @@ function audioContext() {
   return ctx
 }
 
+let noiseBuffer: AudioBuffer | null = null
+function noise(context: AudioContext) {
+  if (!noiseBuffer) {
+    const length = Math.floor(context.sampleRate * 0.05)
+    noiseBuffer = context.createBuffer(1, length, context.sampleRate)
+    const data = noiseBuffer.getChannelData(0)
+    for (let i = 0; i < length; i++) data[i] = Math.random() * 2 - 1
+  }
+  return noiseBuffer
+}
+
 const music = typeof Audio !== 'undefined' ? new Audio() : null
 if (music) music.loop = true
 let currentUrl: string | null = null
@@ -70,6 +81,22 @@ export const audio = {
     osc.connect(gain).connect(context.destination)
     osc.start(now); osc.stop(now + 0.18)
   },
+  // A dry typewriter key-clack, for the text-reveal clatter. Short filtered noise
+  // burst with slight pitch jitter so successive keys differ.
+  type() {
+    if (muted) return
+    const context = audioContext()
+    if (!context) return
+    if (context.state === 'suspended') void context.resume()
+    const src = context.createBufferSource(); src.buffer = noise(context)
+    const filter = context.createBiquadFilter(); filter.type = 'bandpass'; filter.frequency.value = 1500 + Math.random() * 900; filter.Q.value = 0.9
+    const gain = context.createGain()
+    const now = context.currentTime
+    gain.gain.setValueAtTime(0.06, now)
+    gain.gain.exponentialRampToValueAtTime(0.0001, now + 0.028)
+    src.connect(filter).connect(gain).connect(context.destination)
+    src.start(now); src.stop(now + 0.04)
+  },
   // Resume the context and retry pending music on a user gesture.
   resume() {
     void audioContext()?.resume?.()

src/narrative.tsx

@@ -84,6 +84,13 @@ export function DialoguePlayer({ node, onExit, inline, startId }: { node: { utte
     return () => window.clearInterval(id)
   }, [currentId, fullText, reduced]) // eslint-disable-line react-hooks/exhaustive-deps
 
+  // Typewriter clatter as characters are revealed (every other non-space char).
+  useEffect(() => {
+    if (inline || charCount === 0 || charCount > fullText.length) return
+    const ch = fullText[charCount - 1]
+    if (ch && ch !== ' ' && charCount % 2 === 0) audio.type()
+  }, [charCount]) // eslint-disable-line react-hooks/exhaustive-deps
+
   const pick = (choice: RuntimeUtterance) => {
     if (!inline) audio.sfx('choice')
     if (choice.childIds.length > 0) setCurrentId(choice.childIds[0])