# OpenSpec Change: enterprise-audio-transport

- **Change ID**: enterprise-audio-transport
- **Package**: `@suaveplan/audio-transport`
- **Category**: universal
- **Target path**: `packages/audio/audio-transport`
- **Status**: PROPOSED
- **Date**: 2026-05-14
- **Design**: `./design.md`
- **Spec delta**: `./specs/audio-transport/spec.md`

---

## Summary

Deliver `@suaveplan/audio-transport` on the genesis branch from scratch at enterprise quality. The package is a musical clock and transport providing sample-accurate scheduling with PPQ (pulses per quarter), BPM automation, swing, time signatures, and loop regions. It is built on `@suaveplan/timing` for the lookahead scheduler and `@suaveplan/fsm` for playback state. Inspired by Tone.js `Transport`, but universal and injectable.

---

## Current-state audit (genesis)

The package does not exist on genesis yet — this is a fresh build. No prior source, no test results, no coverage data.

---

## Available workspace deps on genesis

| Package | Role |
|---|---|
| `@suaveplan/timing` (`workspace:^`) | `createScheduler`, `Signal`, `FakeClock` for lookahead and tempo curves |
| `@suaveplan/events` (`workspace:^`) | Typed event emitter for `TransportEventMap` |
| `@suaveplan/fsm` (`workspace:^`) | Playback state machine (`stopped` → `playing` → `paused`) |
| `@suaveplan/types` (`workspace:^`) | `LoggerLike`, `Clock` |
| `@suaveplan/error` (`workspace:^`) | Base class for `TransportError`; `AUDIO_TRANSPORT.*` codes |
| `zod` (`catalog:forms`) | Zod schemas for all public option types |

Dev deps: `vitest`, `@vitest/coverage-istanbul`, `fast-check` (all `catalog:testing`).

---

## Public API

### Core types

```ts
interface TransportOptions {
  bpm?: number
  ppq?: number
  swing?: number
  swingSubdivision?: Subdivision
  timeSignature?: number
  loop?: boolean
  loopStart?: TransportTime
  loopEnd?: TransportTime
  logger?: LoggerLike
}

type TransportTime = string | number | Ticks
type Ticks = number
type BarsBeatsSixteenths = string
type BPM = number
type Subdivision = '4n' | '8n' | '16n' | '8t' | '16t'

type TransportCallback = (time: number) => void

interface TransportEventMap {
  start: (time: number) => void
  stop: (time: number) => void
  pause: (time: number) => void
  loop: (time: number) => void
  bpm: (bpm: number, time: number) => void
}

class Transport {
  constructor(options?: TransportOptions)
  get state(): 'stopped' | 'playing' | 'paused'
  get position(): BarsBeatsSixteenths
  get seconds(): number
  get ticks(): number
  start(time?: number, offset?: Ticks): void
  stop(time?: number): void
  pause(time?: number): void
  schedule(callback: TransportCallback, time: TransportTime): number
  scheduleRepeat(callback: TransportCallback, interval: TransportTime, start?: TransportTime): number
  scheduleOnce(callback: TransportCallback, time: TransportTime): number
  cancel(eventId: number): void
  cancelAfter(time: number): void
  bpm: Signal<BPM>
  timeSignature: number
  ppq: number
  loop: boolean
  loopStart: TransportTime
  loopEnd: TransportTime
  swing: number
  swingSubdivision: Subdivision
  toSeconds(time: TransportTime): number
  toTicks(time: TransportTime): Ticks
  toBarsBeatsSixteenths(ticks: Ticks): BarsBeatsSixteenths
  on<K extends keyof TransportEventMap>(event: K, listener: TransportEventMap[K]): void
  off<K extends keyof TransportEventMap>(event: K, listener: TransportEventMap[K]): void
  dispose(): void
}

class TransportScheduler {
  constructor(transport: Transport, clock: Clock)
  start(): void
  stop(): void
}

class TickSource {
  frequency: Signal<'bpm'>
  getTicksAtTime(time: number): Ticks
  getTimeOfTick(tick: Ticks, before?: number): number
  setTicksAtTime(ticks: Ticks, time: number): void
  start(time: number, offset?: Ticks): void
  stop(time: number): void
  pause(time: number): void
  forEachTickBetween(start: number, end: number, callback: (time: number, ticks: Ticks) => void): void
}
```

### Error codes

```ts
type TransportErrorCode =
  | 'AUDIO_TRANSPORT_INVALID_TIME'
  | 'AUDIO_TRANSPORT_INVALID_BPM'
  | 'AUDIO_TRANSPORT_SCHEDULER_NOT_STARTED'
  | 'AUDIO_TRANSPORT_EVENT_NOT_FOUND'
  | 'AUDIO_TRANSPORT_ALREADY_DISPOSED'

const AUDIO_TRANSPORT_ERROR_METADATA: Readonly<Record<TransportErrorCode, CodeMetadata>>
function registerTransportErrorCodes(): void
```

### Zod schemas

```ts
TransportOptionsSchema
TransportTimeSchema
TicksSchema
BarsBeatsSixteenthsSchema
```

---

## File layout

```text
packages/audio/audio-transport/
  package.json
  tsconfig.json
  vitest.config.ts
  src/
    index.ts
    error-codes.ts
    transport/
      transport.ts
      transport.md
      transport.types.ts
      transport.test.ts
      index.ts
    scheduler/
      scheduler.ts
      scheduler.md
      scheduler.types.ts
      scheduler.test.ts
      index.ts
    tick-source/
      tick-source.ts
      tick-source.md
      tick-source.types.ts
      tick-source.test.ts
      index.ts
    signal/
      signal.ts
      signal.md
      signal.types.ts
      signal.test.ts
      index.ts
    time/
      time.ts
      time.md
      time.types.ts
      time.test.ts
      index.ts
    __benchmarks__/
      transport.bench.ts
  tests/
    integration.test.ts
```

---

## Impact

**Breaking changes**: none — fresh build, package does not yet exist on genesis.

**Prerequisites**: `@suaveplan/timing`, `@suaveplan/events`, `@suaveplan/fsm`, `@suaveplan/types`, `@suaveplan/error` published to Verdaccio.

### Affected dependents

`@suaveplan/audio-transport` is consumed by the timeline, both rendering engines, and the
controller packages. At the time of this change none of the dependents exist on genesis yet — they
land in later changes in this same batch — so there is no existing dependent surface to test or
migrate. Each dependent is created against this package's spec delta, not retrofitted.

- `@suaveplan/audio-timeline` — [ ] tests run / [ ] docs reviewed / [x] no action needed (reason: does not exist yet; created in `enterprise-audio-timeline`)
- `@suaveplan/audio-engine-browser` — [ ] tests run / [ ] docs reviewed / [x] no action needed (reason: does not exist yet; created in `enterprise-audio-engine-browser`)
- `@suaveplan/audio-engine-server` — [ ] tests run / [ ] docs reviewed / [x] no action needed (reason: does not exist yet; created in `enterprise-audio-engine-server`)
- `@suaveplan/audio-controllers` — [ ] tests run / [ ] docs reviewed / [x] no action needed (reason: does not exist yet; created in `enterprise-audio-controllers`)

Once landed, any subsequent change to this package's public surface MUST run
`bunx turbo test --filter=...@suaveplan/audio-transport` per `openspec/AGENTS.md` §13 step 10.