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

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+# 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`.