# SIDE B — Lane E2: per-world grooves + SIDE B sound

Read `docs/briefs/SIDEB.md` + `src/core/worlds.ts` first. You own
**`src/audio/**`**. React to bus events only. The main booth groove/stems
engine is yours already — extend, don't fork.

## A1. World grooves (the big one)

On `world:enter {world}`: duck the booth mix out (300 ms) and start that
world's loop; on `world:exit`: reverse. Same synth toolkit (synth.ts), same
shrunk-time BPM feel. Keep each loop 2–4 bars, hypnotic, mixable levels.

- **acid**: 118 BPM, four-on-floor kick + off-hat, and THE 303: a 16-step
  sawtooth acid line through a resonant lowpass (Q high) + accent/slide feel.
  The line's filter cutoff is driven by three bands mapped to
  `fader:move {faderId:'acid_0'|'acid_1'|'acid_2'}` (0..1 from Lane M's
  pedestals): 0 = detuned/wrong (cutoff badly off per-band offsets), target ≈
  band's sweet value (Lane M owns the targets; you just map value→cutoff
  smoothly so sweeping is AUDIBLE and finding the sweet spot is satisfying —
  add a subtle "lock shimmer" layer per locked band via
  `machine:interact {action:'acid_lock'}`). On stamp: the full line + a clap
  layer for 4 bars of glory.
- **dub**: 74 BPM half-time — deep sub bassline, sparse rimshot skank on the
  2/4 through a **feedback echo** (delay ~3/8, feedback 0.55, highcut) and a
  spring-reverb boing patch. `machine:interact {action:'dub_feed'}` = the big
  SPROING (bandpassed noise burst into the echo, feedback momentarily 0.8).
  While carrying the charge (Lane M emits `machine:interact
  {action:'dub_pickup'|'dub_drop'}`): the echo wet rises — you carry the wet.
- **disco**: 122 BPM — four-on-floor, octave bass, offbeat open hat, a little
  string stab loop. `machine:interact {action:'disco_cue', index}` = per-tile
  cue blip (pitch by index, pentatonic); player steps echo the blip a fifth
  down. Stamp = filtered-disco string swell.

## A2. SIDE B SFX + stem tie-ins

- Portal: `world:enter` whoosh-drop (pitch dive + vinyl slow-down effect),
  `world:exit` reverse spin-up.
- `stamp:got`: press-stamp THUNK + one-shot fanfare in that world's key.
- `stamp:all`: golden riser; then permanently add a **bonus percussion stem**
  (shaker/conga layer) to the booth mix (new stem in the stems set, unmuted
  only when stamp:all has fired — persists via Lane M's synced stamp state;
  derive "all stamped" at boot by listening for `stamp:got` count===total or
  an initial re-emit — coordinate exact boot handshake in your handoff).
- `machine:interact {action:'bunny_flee'}`: a shy squeak (soft, quiet, rare).

**Already shipped — coexist, don't rebuild:** emote audio (airhorn etc.),
the reset ritual's power-down collapse, and the zero-repair HEARTBEAT
(commit caac3da) are live. World grooves must duck WHATEVER the booth is
playing — including the heartbeat pre-first-repair — and hand it back on
exit; verify entering a pocket in a dead booth and in a won booth both sound
right, and that a reset while you're inside a pocket doesn't wedge the mix
(the exit handback must re-evaluate booth state, not restore a stale snapshot).

## Verify + handoff

Typecheck clean; extend `demo-audio.html` with a SIDE B panel (world
enter/exit buttons, the three acid faders, dub feed, disco cues, emote pops,
reset) and verify every path by ear + zero console errors in the demo AND a
real-game smoke (launch config `turncraft-laneB` port 5184 if free).
Handoff: `docs/SIDEB_E2_handoff.md` incl. any events you need Lane M to emit
that aren't listed here (coordinate via handoff, not by editing their code).