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/slab/definition.ts

@@ -1,29 +1,24 @@
 import type { NodeDefinition } from '@pascal-app/core'
+import { buildSlabFloorplan } from './floorplan'
+import { buildSlabGeometry } from './geometry'
 import { slabParametrics } from './parametrics'
 import { SlabNode } from './schema'
 
 /**
- * Slab — Phase 5 batch kind, polygon-based.
+ * Slab — Phase 5 batch kind, polygon-based. Stage B: `def.geometry`
+ * drives the rebuild via generic <GeometrySystem>; <ParametricNodeRenderer>
+ * mounts the empty group. No per-kind renderer or system file.
  *
  * Capabilities:
  *  - **No `movable`**: slab's "move" today is whole-slab translation via
  *    legacy `MoveSlabTool`, which integrates with the floor-plan boundary /
- *    hole editors. Per the capability-driven dispatch rule, omitting
- *    `movable` keeps the legacy mover (preserves polygon-aware behavior).
- *    Migration to the generic mover is possible in a later milestone if
- *    the legacy mover proves equivalent.
+ *    hole editors. Capability-driven dispatch keeps the legacy mover.
  *  - **`surfaces.top`**: items host on the slab top at `elevation`.
  *  - `selectable`, `duplicable`, `deletable` standard.
  *
  * Relations:
  *  - `hosts: ['item']` — items mount on the slab top.
  *  - `cascadeDelete: 'descendants'` — deleting a slab removes hosted items.
- *
- * Renderer + system: thin renderer + re-export of the legacy `SlabSystem`.
- * Same shape as wall / fence runtime port.
- *
- * Tool field absent: slab has 3 tools (slab-tool, boundary-editor, hole-
- * editor) wired through editor state, not registry dispatch.
  */
 export const slabDefinition: NodeDefinition<typeof SlabNode> = {
   kind: 'slab',
@@ -59,14 +54,11 @@ export const slabDefinition: NodeDefinition<typeof SlabNode> = {
 
   parametrics: slabParametrics,
 
-  renderer: {
-    kind: 'parametric',
-    module: () => import('./renderer'),
-  },
-  system: {
-    module: () => import('./system'),
-    priority: 4,
-  },
+  // Stage B: pure geometry function.
+  geometry: buildSlabGeometry,
+  // Stage C: floor-plan rendering. Legacy `slabPolygons` short-circuits
+  // to [] when slab is registered (see floorplan-panel.tsx).
+  floorplan: buildSlabFloorplan,
 
   toolHints: [
     { key: 'Left click', label: 'Trace slab outline' },