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openspec/changes/enterprise-gaming-day-night/proposal.md

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+# OpenSpec Change: enterprise-gaming-day-night
+
+- **Change ID**: enterprise-gaming-day-night
+- **Package**: `@suaveplan/day-night`
+- **Category**: gaming/world
+- **Target path**: `gaming/world/day-night`
+- **Status**: PROPOSED
+- **Date**: 2026-04-24
+- **Reference spec**: `/mnt/s/web/suaveplan/enterprise/day-night.md`
+
+---
+
+## Summary
+
+Deliver `@suaveplan/day-night` on the genesis branch from scratch at enterprise quality. The package provides a day/night cycle with configurable time scale, sun/moon position math, light schedule interpolation, and gameplay effect modifiers. `DayNightClock` advances in-game time at a configurable multiple of real time; `SkyPositionCalculator` computes sun and moon azimuth/elevation from in-game time using a simplified celestial model; `LightSchedule` keyframes ambient light color and intensity across the day; `GameplayModifiers` maps time-of-day segments to gameplay effect multipliers (spawn rate, visibility, economy). Genesis adds Zod schemas, structured errors, OTel time counter, injectable clock, 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:^`) | `DayNightError`; `DAY_NIGHT.*` codes |
+| `@suaveplan/types` (`workspace:^`) | `Clock` |
+| `@suaveplan/events` (`workspace:^`) | `time:dawn`, `time:noon`, `time:dusk`, `time:midnight` events |
+| `zod` (`catalog:forms`) | `LightSchedule`, `GameplayModifiers` schemas |
+| `@opentelemetry/api` (`catalog:observability`) | In-game time gauge |
+
+---
+
+## Public API surface
+
+```ts
+function createDayNightClock(options: DayNightClockOptions): DayNightClock
+
+interface DayNightClockOptions {
+  timeScale?: number          // real seconds per in-game minute, default 1 min = 1 sec
+  initialHour?: number        // 0–24
+  clock?: Clock
+}
+
+interface DayNightClock {
+  tick(dt: number): void
+  readonly hour: number       // 0–24 fractional
+  readonly dayCount: number
+  setHour(hour: number): void
+  pause(): void
+  resume(): void
+  readonly isPaused: boolean
+}
+
+interface SkyPosition {
+  azimuth: number       // degrees
+  elevation: number     // degrees (-90 to 90)
+  intensity: number     // 0–1
+}
+
+function computeSunPosition(hour: number): SkyPosition
+function computeMoonPosition(hour: number): SkyPosition
+
+// Light schedule
+interface LightKeyframe {
+  hour: number
+  ambientColor: [r: number, g: number, b: number]
+  ambientIntensity: number
+  fogDensity?: number
+}
+
+function createLightSchedule(keyframes: LightKeyframe[]): LightSchedule
+interface LightSchedule {
+  evaluate(hour: number): LightKeyframe
+}
+
+// Gameplay modifiers
+interface TimeModifier {
+  fromHour: number
+  toHour: number
+  spawnRateMultiplier?: number
+  visibilityMultiplier?: number
+  economyMultiplier?: number
+  label?: string
+}
+
+function createGameplayModifiers(modifiers: TimeModifier[]): GameplayModifiers
+interface GameplayModifiers {
+  evaluate(hour: number): TimeModifier & Required<Omit<TimeModifier, 'label' | 'fromHour' | 'toHour'>>
+}
+```
+
+### Error codes
+
+```ts
+type DayNightErrorCode =
+  | 'DAY_NIGHT_INVALID_HOUR'
+  | 'DAY_NIGHT_SCHEDULE_EMPTY'
+  | 'DAY_NIGHT_KEYFRAME_GAP'
+```
+
+---
+
+## File layout
+
+```text
+gaming/world/day-night/
+  package.json
+  tsconfig.json
+  vitest.config.ts
+  src/
+    index.ts
+    error-codes.ts
+    constants/index.ts
+    types/common.ts
+    types/common.md
+    core/
+      day-night-clock/
+        day-night-clock.ts
+        day-night-clock.md
+        day-night-clock.types.ts
+        day-night-clock.test.ts
+        index.ts
+      light-schedule/
+        light-schedule.ts
+        light-schedule.md
+        light-schedule.types.ts
+        light-schedule.test.ts
+        index.ts
+      gameplay-modifiers/
+        gameplay-modifiers.ts
+        gameplay-modifiers.md
+        gameplay-modifiers.types.ts
+        gameplay-modifiers.test.ts
+        index.ts
+    utils/
+      sky-position.ts
+      sky-position.md
+      sky-position.test.ts
+  tests/
+    integration.test.ts
+```
+
+---
+
+## Impact
+
+**Downstream**: `@suaveplan/r3f-environment` uses sun/moon positions for directional light; `@suaveplan/weather` reads time for weather transitions. Prerequisites: `@suaveplan/error`, `@suaveplan/types`, `@suaveplan/events`.