feat(editor): live floor-stacking, unified handle system, slab-hole editing + interaction polish (#375)

- Live slab-stacking Y previews for all floor-placed kinds (item/shelf/spawn/column/stair) during placement + both move pathways, via a shared core resolver; canonical positions unchanged.
- Unified 3D handle system (one drag pipeline + one visual primitive) with forgiving invisible hit-areas on every handle, kept on EDITOR_LAYER so they don't poison the MRT scene pass.
- Hover + click-to-edit slab holes in 3D (manual hole -> hole editor; stair/elevator hole -> select owner); generic cross-arrow polygon-move grip; normalized handle interaction colors.
- NaN-safe node mutations + non-finite shadow-light bounds guard.
- Built on #373 (level-scoped alignment / registry slab tool); #373 owns X/Z alignment, this owns Y floor-stacking.

packages/nodes/src/shelf/definition.ts

@@ -1,4 +1,5 @@
 import type { HandleDescriptor, NodeDefinition, ShelfNode as ShelfNodeType } from '@pascal-app/core'
+import { sanitizeShelfDimensions } from './dimensions'
 import { buildShelfFloorplan } from './floorplan'
 import { shelfResizeAffordance, shelfRotateAffordance } from './floorplan-affordances'
 import { shelfFloorplanMoveTarget } from './floorplan-move'
@@ -10,6 +11,7 @@ const SIDE_HANDLE_OFFSET = 0.18
 const HEIGHT_HANDLE_OFFSET = 0.22
 const ROTATE_CORNER_OFFSET = 0.32
 const ROTATE_RING_OFFSET = 0.04
+const MOVE_FRONT_OFFSET = 0.35
 const MIN_SHELF_WIDTH = 0.3
 const MIN_SHELF_DEPTH = 0.1
 const MIN_SHELF_HEIGHT = 0.05
@@ -95,8 +97,35 @@ function shelfRotateHandle(): HandleDescriptor<ShelfNodeType> {
   }
 }
 
+function shelfMoveHandle(): HandleDescriptor<ShelfNodeType> {
+  return {
+    kind: 'translate',
+    placement: {
+      // Low to the floor at the front edge (matches the item move grip) so it
+      // reads as a floor-move grip and stays clear of the body resize / rotate
+      // handles that sit at mid-height.
+      position: (n) => {
+        const shelf = sanitizeShelfDimensions(n as ShelfNode)
+        return [0, 0.02, shelf.depth / 2 + MOVE_FRONT_OFFSET]
+      },
+    },
+    apply: (_n, pos) => ({ position: [pos[0], pos[1], pos[2]] }),
+    snapExtents: (n) => {
+      const shelf = sanitizeShelfDimensions(n as ShelfNode)
+      const swap = Math.abs(Math.sin(shelf.rotation[1] ?? 0)) > 0.9
+      return [swap ? shelf.depth : shelf.width, swap ? shelf.width : shelf.depth]
+    },
+  }
+}
+
 function shelfHandles(_node: ShelfNodeType): HandleDescriptor<ShelfNodeType>[] {
-  return [shelfWidthHandle(), shelfDepthHandle(), shelfHeightHandle(), shelfRotateHandle()]
+  return [
+    shelfWidthHandle(),
+    shelfDepthHandle(),
+    shelfHeightHandle(),
+    shelfRotateHandle(),
+    shelfMoveHandle(),
+  ]
 }
 
 export const shelfDefinition: NodeDefinition<typeof ShelfNode> = {
@@ -158,7 +187,7 @@ export const shelfDefinition: NodeDefinition<typeof ShelfNode> = {
     // shelf sitting over a raised slab visually rests on top of it.
     floorPlaced: {
       footprint: (node) => {
-        const shelf = node as ShelfNode
+        const shelf = sanitizeShelfDimensions(node as ShelfNode)
         return {
           dimensions: [shelf.width, shelf.height, shelf.depth] as [number, number, number],
           rotation: shelf.rotation,
@@ -189,7 +218,7 @@ export const shelfDefinition: NodeDefinition<typeof ShelfNode> = {
   // `children`. Lets <GeometrySystem> skip the dispose+rebuild (and the
   // pointer enter/leave churn it causes) when an item reparents onto a row.
   geometryKey: (n) => {
-    const s = n as ShelfNodeType
+    const s = sanitizeShelfDimensions(n as ShelfNode)
     return JSON.stringify([
       s.style,
       s.width,