# LANE E — UI / HUD / Audio engine

Mission: the instrument you fly by. Diegetic scanner HUD, screens, and the WebAudio engine
that plays D's pack (or synthesizes fallbacks). You own `web/js/ui/**` and `web/js/audio/**`.

## HUD (ART_BIBLE §Screens: thin cyan line-work, small caps, data-noise ticks)

- Core readouts: mucus-coat + hull bars, heat meter, torpedo count, speed/flow indicator,
  combo meter, score. All driven by **bus events only** (TECH §Bus) — zero imports from
  B's internals; if a signal is missing, request the event in NOTES, don't reach in.
- **The gut-map** (the star): full alimentary-canal silhouette as the campaign progress
  bar — current level lit, player blip moving along it, checkpoints ticked. One SVG/canvas
  path, hand-drawn once, used everywhere (title, HUD corner, level-complete).
- Telegraphs: upstream-hazard pings for C (spec: `level:event` lookahead), boss health
  when `boss:start`.
- **Damage = feed corruption** (aberration/tearing via F's post hooks + your overlay
  glitches), not red vignette. Death/respawn = feed drop + re-acquire sequence. Cheap DOM/
  canvas overlay preferred over three.js sprites — it's an instrument overlay, let it be 2D.
- Screens: title (over `?fly=1`-style esophagus drift), pause, level-complete medal card
  (score/par/samples — GDD §Scoring), game-over, minimal settings (difficulty, assists,
  volume, `?mute` respect).

## Audio engine (`js/audio/engine.js`)

- WebAudio graph: bed bus (crossfade per `biomeAt` changes), sfx bus (pooled buffers),
  stinger duck. Autoplay-unlock on first input (browser law).
- Consumes D's manifest audio (`ogg` with `m4a` fallback via `canPlayType`). **Procedural
  fallback law:** no pack ⇒ synthesized WebAudio beeps/noise bursts so the game is never
  silent-broken (`assets.get` null path).
- The heartbeat: a low pulse bed whose **tempo maps to danger** (combo/boss/coat-low —
  define the danger scalar from bus events, document the mapping). This is the audio
  identity of the game; treat it as a headline feature.
- Sync hook: `world.flowPulse` phase available for pulse-aligned squelches (nice-to-have,
  round 2+).

## You owe / consume

Owe: `createHUD/createScreens/createAudio` factories (TECH convention), the event-needs
list in NOTES (B and C build to it), volume/mute persistence (localStorage). Consume: bus
events, D's audio manifest, ART_BIBLE, F's post-processing hooks for damage fx.

## Laws

60 fps law applies to the HUD too — no per-frame DOM layout thrash (mutate via transforms/
canvas; measure with `?dbg=1`). Everything disposes (screens swap clean). Screenshots of
every screen + HUD states in `docs/shots/laneE/`; audio evidence = the engine playing D's
spectrogram-verified pack + a written fallback-mode check.
