Phase 5 depth-first: spawn C, fence B+C, slab B+C, ceiling C

Depth-first session: drive registered kinds through Stage B (pure
def.geometry, drop system re-export) and Stage C (def.floorplan,
short-circuit legacy inline rendering in floorplan-panel.tsx).

spawn → C
 - buildSpawnFloorplan wired on definition (was written but deferred
   to avoid double-render).
 - floorplan-panel.tsx's floorplanSpawnEntries useMemo short-circuits
   to [] when nodeRegistry.has('spawn').

fence → B
 - generateFenceGeometry exported from viewer; buildFenceGeometry
   wraps it in a Group+Mesh with DEFAULT_STAIR_MATERIAL.
 - def.geometry set; renderer + system fields dropped.
 - Deleted nodes/src/fence/{renderer.tsx,system.tsx}.

fence → C
 - buildFenceFloorplan: polyline along centerline (sampled for curved
   fences via sampleWallCenterline from core). Stroke width = node.thickness.
 - floorplan-panel.tsx's floorplanFenceEntries short-circuits.

slab → B
 - generateSlabGeometry exported from viewer; buildSlabGeometry wraps
   it in a Group+Mesh + cached material (preset / custom / default
   pattern preserved from legacy renderer).
 - def.geometry set; renderer + system fields dropped.
 - Deleted nodes/src/slab/{renderer.tsx,system.tsx}.

slab → C
 - buildSlabFloorplan: SVG path with outer polygon + hole subpaths
   (uses getRenderableSlabPolygon from core for wall-clipping parity).
 - floorplan-panel.tsx's slabPolygons short-circuits.

ceiling → B INTENTIONALLY SKIPPED
 - Ceiling renderer renders React children (hosted items) + uses TSL
   shader materials + named meshes that other systems poke
   (getObjectByName('ceiling-grid')). Pure def.geometry can't preserve
   that. Ceiling keeps def.renderer (the custom escape hatch) — same
   pattern item uses. Documented in ceiling/definition.ts.

ceiling → C
 - buildCeilingFloorplan: dashed-outline path with hole subpaths
   (visually distinct from slab since ceilings are above).
 - floorplan-panel.tsx's ceilingPolygons short-circuits.

Per-kind progress after this session:
 - shelf: B ✅ C ✅ (Stage E since brand-new)
 - spawn: A ✅ C ✅
 - wall: A ✅ (B blocked on ctx.levelData design)
 - fence: A ✅ B ✅ C ✅
 - slab: A ✅ B ✅ C ✅
 - ceiling: A ✅ C ✅ (B intentionally not applicable)
 - door / window / item: A ✅ (B+C pending in future sessions)

Known test issue: `bun test` in packages/nodes fails to load
`three-bvh-csg` through the viewer's transitive imports (UMD/ESM
mismatch in Bun's test runner). The Next.js editor build works fine
because it bundles differently. Fix requires either dynamic imports
(breaks sync def.geometry contract) or test env config — deferred.
Other tests (schema, geometry, parity) pass.

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

packages/nodes/src/spawn/definition.ts

@@ -1,4 +1,5 @@
 import type { NodeDefinition } from '@pascal-app/core'
+import { buildSpawnFloorplan } from './floorplan'
 import { spawnParametrics } from './parametrics'
 import { SpawnNode } from './schema'
 
@@ -34,12 +35,14 @@ export const spawnDefinition: NodeDefinition<typeof SpawnNode> = {
     kind: 'parametric',
     module: () => import('./renderer'),
   },
-  // `floorplan: buildSpawnFloorplan` deferred — spawn already renders in
-  // the legacy floorplan-panel.tsx via `floorplanSpawnEntries`. Adding it
-  // here would double-render. The pure builder lives in
-  // ./floorplan.ts ready to wire when the legacy inline branch is
-  // removed (Phase 5 spawn-floorplan migration PR — same shape as the
-  // wall feature flag, but per kind in the legacy panel itself).
+  // Stage C migration: floor-plan rendering via def.floorplan.
+  // floorplan-panel.tsx's `floorplanSpawnEntries` short-circuits to []
+  // when `nodeRegistry.has('spawn')`, so this builder is the single
+  // path. FloorplanRegistryLayer renders + handles click-to-select;
+  // FloorplanRegistryActionMenu handles move / duplicate (disabled) /
+  // delete. Legacy spawn click handlers in FloorplanNodeLayer become
+  // dead code once Phase 6 cleanup removes the [] entries path.
+  floorplan: buildSpawnFloorplan,
   tool: () => import('./tool'),
   toolHints: [
     { key: 'Left click', label: 'Place spawn point' },