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openspec/changes/enterprise-gaming-building/proposal.md

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+# OpenSpec Change: enterprise-gaming-building
+
+- **Change ID**: enterprise-gaming-building
+- **Package**: `@suaveplan/building`
+- **Category**: gaming/world
+- **Target path**: `gaming/world/building`
+- **Status**: PROPOSED
+- **Date**: 2026-04-24
+- **Reference spec**: `/mnt/s/web/suaveplan/enterprise/building.md`
+
+---
+
+## Summary
+
+Deliver `@suaveplan/building` on the genesis branch from scratch at enterprise quality. The package provides a player building system with snap placement, structural integrity simulation, and blueprint serialization. A `BuildingPieceRegistry` holds typed piece descriptors (walls, floors, roofs, foundations); a `PlacementEngine` validates snap socket connections and surface collisions; a `StructureGraph` tracks piece adjacency for structural integrity (floating pieces detected by DFS); `Blueprint` captures a structure as a serializable set of piece instances. Genesis adds Zod piece schemas, structured errors, OTel placement 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:^`) | `BuildingError`; `BUILDING.*` codes |
+| `@suaveplan/types` (`workspace:^`) | `IdGenerator` |
+| `@suaveplan/events` (`workspace:^`) | `building:placed`, `building:removed`, `building:unstable` events |
+| `@suaveplan/serialize` (`workspace:^`) | Blueprint serialization |
+| `zod` (`catalog:forms`) | Piece descriptor + blueprint schemas |
+| `@opentelemetry/api` (`catalog:observability`) | Piece count gauge, placement counter |
+
+---
+
+## Public API surface
+
+```ts
+type PieceCategory = 'foundation' | 'wall' | 'floor' | 'roof' | 'door' | 'window' | 'stair' | 'decoration'
+
+interface SnapSocket {
+  id: string
+  position: Vec3           // local space offset from piece center
+  rotation: Quat
+  acceptsCategories: PieceCategory[]
+}
+
+interface PieceDescriptor {
+  id: string
+  name: string
+  category: PieceCategory
+  sockets: SnapSocket[]
+  bounds: { min: Vec3; max: Vec3 }
+  health: number
+  resourceCost?: Record<string, number>
+}
+
+function createBuildingPieceRegistry(): BuildingPieceRegistry
+interface BuildingPieceRegistry {
+  register(piece: PieceDescriptor): void
+  get(id: string): PieceDescriptor | undefined
+  listByCategory(category: PieceCategory): PieceDescriptor[]
+}
+
+interface PieceInstance {
+  instanceId: string
+  pieceId: string
+  position: Vec3
+  rotation: Quat
+  health: number
+  connectedTo: string[]   // instanceIds of adjacent pieces
+}
+
+function createPlacementEngine(registry: BuildingPieceRegistry): PlacementEngine
+
+interface PlacementEngine {
+  findSnap(piece: PieceDescriptor, cursorPosition: Vec3, existingPieces: PieceInstance[]): SnapResult | null
+  validatePlacement(pieceId: string, position: Vec3, rotation: Quat, existingPieces: PieceInstance[]): ValidationResult
+  place(pieceId: string, position: Vec3, rotation: Quat): PieceInstance
+}
+
+interface SnapResult {
+  position: Vec3
+  rotation: Quat
+  socketId: string
+  targetInstanceId: string
+}
+
+interface ValidationResult {
+  valid: boolean
+  reason?: string
+}
+
+function createStructureGraph(): StructureGraph
+interface StructureGraph {
+  addPiece(instance: PieceInstance): void
+  removePiece(instanceId: string): void
+  getUnstable(): string[]    // instanceIds with no path to foundation
+  isStable(): boolean
+}
+
+// Blueprint
+function captureBlueprint(pieces: PieceInstance[]): Blueprint
+function applyBlueprint(blueprint: Blueprint, origin: Vec3): PieceInstance[]
+
+interface Blueprint {
+  id: string
+  name: string
+  pieces: Array<{ pieceId: string; relativePosition: Vec3; rotation: Quat }>
+  createdAt: number
+}
+```
+
+### Error codes
+
+```ts
+type BuildingErrorCode =
+  | 'BUILDING_PIECE_NOT_FOUND'
+  | 'BUILDING_PLACEMENT_INVALID'
+  | 'BUILDING_NO_FOUNDATION'
+  | 'BUILDING_UNSTABLE'
+  | 'BUILDING_SOCKET_MISMATCH'
+```
+
+---
+
+## File layout
+
+```text
+gaming/world/building/
+  package.json
+  tsconfig.json
+  vitest.config.ts
+  src/
+    index.ts
+    error-codes.ts
+    constants/index.ts
+    types/common.ts
+    types/common.md
+    core/
+      piece-registry/
+        piece-registry.ts
+        piece-registry.md
+        piece-registry.test.ts
+        index.ts
+      placement-engine/
+        placement-engine.ts
+        placement-engine.md
+        placement-engine.types.ts
+        placement-engine.test.ts
+        index.ts
+      structure-graph/
+        structure-graph.ts
+        structure-graph.md
+        structure-graph.types.ts
+        structure-graph.test.ts
+        index.ts
+      blueprint/
+        blueprint.ts
+        blueprint.md
+        blueprint.types.ts
+        blueprint.test.ts
+        index.ts
+  tests/
+    integration.test.ts
+```
+
+---
+
+## Impact
+
+**Downstream**: `@suaveplan/r3f-building` renders ghost preview and placed pieces. Prerequisites: `@suaveplan/error`, `@suaveplan/types`, `@suaveplan/events`, `@suaveplan/serialize`.