suaveplan/openspec/changes/enterprise-gaming-animation-events/proposal.md

# OpenSpec Change: enterprise-gaming-animation-events

- **Change ID**: enterprise-gaming-animation-events
- **Package**: `@suaveplan/animation-events`
- **Category**: gaming/rigs
- **Target path**: `gaming/rigs/animation-events`
- **Status**: PROPOSED
- **Date**: 2026-04-24
- **Reference spec**: `/mnt/s/web/suaveplan/enterprise/animation-events.md`

---

## Summary

Deliver `@suaveplan/animation-events` on the genesis branch from scratch at enterprise quality. The package provides animation event dispatching, foot contact detection, and procedural animation modifiers. An `AnimationEventTrack` associates named events with normalized animation times (0–1); an `AnimationEventDispatcher` fires `@suaveplan/events` messages when playback crosses event timestamps. `FootContactDetector` analyses Y-velocity of ankle bones to determine ground contact frames. Procedural modifiers (head bob, breathing sway, aim offset) compose additively. Genesis adds Zod schemas, structured errors, OTel event-count counter, and 100% coverage.

---

## Current-state audit (genesis)

Package does not exist on genesis yet — fresh build.

---

## Available workspace deps on genesis

| Package | Role |
|---|---|
| `@suaveplan/error` (`workspace:^`) | `AnimationEventsError`; `ANIM_EVENT.*` codes |
| `@suaveplan/types` (`workspace:^`) | `Clock` |
| `@suaveplan/events` (`workspace:^`) | Event bus for dispatching animation triggers |
| `@suaveplan/ik-solver` (`workspace:^`) | `solveLookAt` for aim-offset modifier |
| `zod` (`catalog:forms`) | Track and modifier schemas |
| `@opentelemetry/api` (`catalog:observability`) | Event dispatch counter |

---

## Public API surface

```ts
// Event track
interface AnimationEvent {
  name: string
  normalizedTime: number   // 0–1
  data?: unknown
}

function createEventTrack(events: AnimationEvent[]): AnimationEventTrack

interface AnimationEventTrack {
  getEvents(fromNorm: number, toNorm: number): AnimationEvent[]
  readonly events: readonly AnimationEvent[]
}

// Dispatcher
function createAnimationEventDispatcher(options: DispatcherOptions): AnimationEventDispatcher

interface DispatcherOptions {
  eventBus: EventBusLike
  namespace?: string    // event name prefix, default 'anim'
}

interface AnimationEventDispatcher {
  update(clipName: string, track: AnimationEventTrack, normalizedTime: number, prevNormalizedTime: number): void
}

// Foot contact detection
function createFootContactDetector(options: FootContactOptions): FootContactDetector

interface FootContactOptions {
  ankleThresholdY?: number    // velocity below which foot is considered planted, default 0.05
  sampleWindow?: number       // frames to average, default 3
}

interface FootContactDetector {
  update(leftAnkleY: number, rightAnkleY: number, dt: number): FootContactState
}

interface FootContactState {
  leftGrounded: boolean
  rightGrounded: boolean
  leftPlantedAt?: Vec3
  rightPlantedAt?: Vec3
}

// Procedural modifiers
interface ProceduralModifier {
  update(dt: number, input: ModifierInput): BonePose[]
}

function createHeadBobModifier(options: HeadBobOptions): ProceduralModifier
function createBreathingModifier(options: BreathingOptions): ProceduralModifier
function createAimOffsetModifier(options: AimOffsetOptions): ProceduralModifier
```

### Error codes

```ts
type AnimEventErrorCode =
  | 'ANIM_EVENT_TRACK_EMPTY'
  | 'ANIM_EVENT_INVALID_TIME'
  | 'ANIM_EVENT_DISPATCH_FAILED'
```

---

## New additions for genesis

1. **Looping event detection** — dispatcher handles wrap-around (prevNorm > normTime) correctly, firing events in the wrapped range.
2. **Foot IK plant correction** — `FootContactDetector` outputs planted world positions; caller feeds into `@suaveplan/ik-solver` for foot placement.
3. **Aim offset modifier** — uses `solveLookAt` to rotate spine/neck toward aim target additively.

---

## File layout

```text
gaming/rigs/animation-events/
  package.json
  tsconfig.json
  vitest.config.ts
  src/
    index.ts
    error-codes.ts
    constants/index.ts
    types/common.ts
    types/common.md
    core/
      event-track/
        event-track.ts
        event-track.md
        event-track.types.ts
        event-track.test.ts
        index.ts
      dispatcher/
        dispatcher.ts
        dispatcher.md
        dispatcher.types.ts
        dispatcher.test.ts
        index.ts
      foot-contact/
        foot-contact.ts
        foot-contact.md
        foot-contact.types.ts
        foot-contact.test.ts
        index.ts
    modifiers/
      head-bob/
        head-bob.ts
        head-bob.md
        head-bob.test.ts
        index.ts
      breathing/
        breathing.ts
        breathing.md
        breathing.test.ts
        index.ts
      aim-offset/
        aim-offset.ts
        aim-offset.md
        aim-offset.test.ts
        index.ts
  tests/
    integration.test.ts
```

---

## Impact

**Downstream**: `@suaveplan/r3f-animation` hooks these modifiers into Three.js AnimationMixer. Prerequisites: `@suaveplan/error`, `@suaveplan/types`, `@suaveplan/events`, `@suaveplan/ik-solver`.