Phase 5 Stage C continued: wall, door, window now in registry floor plan

Three remaining kinds at Stage C this session:

wall → C
 - buildWallFloorplan: uses ctx.siblings to gather other walls in the
   level, runs calculateLevelMiters, computes plan footprint via
   getWallPlanFootprint. Same visual output as legacy.
 - getFloorplanWall thickness exaggeration inlined (~25 lines from
   editor/lib/floorplan/walls.ts) to keep nodes/wall self-contained.
 - floorplan-panel.tsx's wallPolygons short-circuits to [] when wall
   is registered.
 - Performance note: recomputes level miter data per wall (O(N²) for N
   walls in a level). Acceptable for typical scenes; ctx.levelData?.
   miters optimization deferred to Stage B's wall design pass.

door → C
 - buildDoorFloorplan: inlines getOpeningFootprint math from
   floorplan-panel.tsx (40 lines, pure math). Uses ctx.parent as the
   wall to compute direction + perpendicular for the cutout footprint.
 - Returns null when parent isn't a wall (orphaned doors during
   placement).

window → C
 - buildWindowFloorplan: same shape as door, glass-blue tint to
   distinguish visually.

Both share the legacy openingsPolygons gating:
 - floorplan-panel.tsx's openingsPolygons useMemo filters per kind so
   a partial migration still works (e.g., if only door registers, only
   doors get skipped). When both registered, returns [] entirely.

Item C intentionally deferred — needs parent-chain transform helpers
(buildFloorplanItemEntry / getItemFloorplanTransform from editor/lib/
floorplan/items.ts) exposed publicly or moved into core. A focused
session is the right place to design that boundary.

Stage B for door / window / wall still pending — each is a focused
session per kind (large geometry math extractions, wall needs ctx.
levelData design).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/nodes/src/window/definition.ts

@@ -1,4 +1,5 @@
 import type { NodeDefinition } from '@pascal-app/core'
+import { buildWindowFloorplan } from './floorplan'
 import { windowParametrics } from './parametrics'
 import { WindowNode } from './schema'
 
@@ -6,8 +7,12 @@ import { WindowNode } from './schema'
  * Window — Phase 5 batch kind. Mirrors door's shape: hosted on walls,
  * cuts holes in them, animated open/close state for opening windows.
  *
- * Capabilities: no `movable` (wall-bound drag is bespoke). Tool field
- * absent (legacy WindowTool / MoveWindowTool continue).
+ * Stages:
+ *  - A: registered.
+ *  - B: deferred — window geometry ~800 lines; extraction is a focused
+ *    session. `def.renderer` + `def.system` wrap-export legacy.
+ *  - C: `def.floorplan` polygon sits in parent wall's cutout. Legacy
+ *    `openingPolygons` short-circuits window entries when registered.
  */
 export const windowDefinition: NodeDefinition<typeof WindowNode> = {
   kind: 'window',
@@ -39,6 +44,9 @@ export const windowDefinition: NodeDefinition<typeof WindowNode> = {
     module: () => import('./system'),
     priority: 3,
   },
+  // Stage C: floor-plan polygon. ctx.parent gives the wall for direction
+  // + thickness — same shape as door.
+  floorplan: buildWindowFloorplan,
 
   toolHints: [
     { key: 'Left click', label: 'Place window on wall' },