Phase 5 Stage D: fix bend history + move-tool loop + grid-snap sfx

Three user-reported regressions, all in the Stage D move/curve ports:

1. **Fence/wall bend cancelled the fence creation on Ctrl-Z.** The
   action.commit's `return false` shortcut on "no offset change"
   bypassed the dance entirely — pastStates wasn't touched, so the
   next Ctrl-Z fell through to whatever preceded activation
   (typically the create step). Fix: always run the dance, even on
   no-op commits. First Ctrl-Z then absorbs a silent no-op entry,
   subsequent presses roll back real prior actions. Same fix applied
   to fence move-endpoint, fence move, slab move, ceiling move.

2. **Slab/ceiling move 'maximum update depth exceeded' loop.** The
   `useScene` selector in `SlabMoveTool` returned a freshly-allocated
   `[sx, sz]` tuple on every call. Zustand's `Object.is` equality
   failed each comparison → re-subscribe → re-render → loop. Fix:
   subscribe to the stable live-node reference and derive the center
   via `useMemo`. Same recipe for fence/ceiling move-tools, including
   memoizing the `originalCenter` fallback that was getting a new
   array per render.

3. **No grid-snap sfx during move drag.** Action `preview` now tracks
   the last snapped pointer on a mutable `lastSnapped` ctx field and
   emits `sfx:grid-snap` when it changes between ticks. Matches the
   legacy MoveFenceTool's per-tick sound.

Locking test for foot-gun 1 lives in
`packages/core/src/services/single-undo-dance.test.ts`.

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

packages/nodes/src/ceiling/actions/move.ts

@@ -1,4 +1,5 @@
 import type { AnyNode, AnyNodeId, CeilingNode, DragAction } from '@pascal-app/core'
+import { triggerSFX } from '@pascal-app/editor'
 
 /**
  * Phase 5 Stage D — whole-ceiling move drag affordance.
@@ -6,7 +7,8 @@ import type { AnyNode, AnyNodeId, CeilingNode, DragAction } from '@pascal-app/co
  * Mirrors `slab/actions/move.ts` shape but ceiling snaps purely to a
  * 0.5m grid (no wall/fence corner snap — ceilings are typically
  * placed independent of the floor layout). Drag anchor is latched on
- * the first preview tick so the ceiling doesn't jump.
+ * the first preview tick so the ceiling doesn't jump. Emits a grid-
+ * snap sfx when the snapped position changes between ticks.
  *
  * Single-undo dance on commit, same recipe as slab/fence.
  */
@@ -17,6 +19,10 @@ function snap(value: number): number {
   return Math.round(value / GRID_STEP) * GRID_STEP
 }
 
+function sameSnap(a: [number, number] | null, b: [number, number]): boolean {
+  return a !== null && a[0] === b[0] && a[1] === b[1]
+}
+
 function translatePolygon(
   polygon: Array<[number, number]>,
   deltaX: number,
@@ -30,6 +36,7 @@ export type MoveCeilingCtx = {
   originalPolygon: Array<[number, number]>
   originalHoles: Array<Array<[number, number]>>
   dragAnchor: [number, number] | null
+  lastSnapped: [number, number] | null
 }
 
 export type MoveCeilingDraft = {
@@ -50,13 +57,19 @@ export const moveCeilingDragAction: DragAction<MoveCeilingCtx, MoveCeilingDraft>
         h.map(([x, z]) => [x, z] as [number, number]),
       ),
       dragAnchor: null,
+      lastSnapped: null,
     }
   },
 
   preview: (ctx, point, _modifiers) => {
     const sx = snap(point[0])
     const sz = snap(point[1])
-    if (!ctx.dragAnchor) ctx.dragAnchor = [sx, sz]
+    const snapped: [number, number] = [sx, sz]
+    if (!sameSnap(ctx.lastSnapped, snapped)) {
+      if (ctx.lastSnapped !== null) triggerSFX('sfx:grid-snap')
+      ctx.lastSnapped = snapped
+    }
+    if (!ctx.dragAnchor) ctx.dragAnchor = snapped
     const deltaX = sx - ctx.dragAnchor[0]
     const deltaZ = sz - ctx.dragAnchor[1]
     return {
@@ -76,7 +89,9 @@ export const moveCeilingDragAction: DragAction<MoveCeilingCtx, MoveCeilingDraft>
   },
 
   commit: (draft, ctx, scene) => {
-    if (draft.deltaX === 0 && draft.deltaZ === 0) return false
+    // Always push — see fence/actions/curve.ts. No-movement still
+    // records a pastState entry so Ctrl-Z doesn't fall through to the
+    // ceiling-create step.
     scene.restoreAll()
     scene.resumeHistory()
     scene.update(ctx.ceilingId, {

packages/nodes/src/ceiling/move-tool.tsx

@@ -22,7 +22,11 @@ export const CeilingMoveTool: React.FC<{ node: CeilingNode }> = ({ node }) => {
   const live = useScene((s) => s.nodes[ceilingId])
   const liveCeiling = live?.type === 'ceiling' ? (live as CeilingNode) : node
   const polygon = liveCeiling.polygon
-  const holes = liveCeiling.holes ?? []
+  // `?? []` would return a NEW empty array per render, busting downstream
+  // useMemo deps and (under StrictMode) potentially triggering the
+  // "getSnapshot result not cached" warning. Memoize against the source.
+  const EMPTY_HOLES = useMemo(() => [] as Array<Array<[number, number]>>, [])
+  const holes = liveCeiling.holes ?? EMPTY_HOLES
 
   const center: [number, number] = useMemo(() => {
     if (polygon.length === 0) return [0, 0]