refactor: drop NodeLayout.collapsedSize, keep it on the ynode only

collapsedSize was added to NodeLayout earlier in this PR as a first-class
field alongside a special-case tail in yNodeToLayout. Nothing outside of
the mapper actually reads it via the layout shape — measure() goes
through LiteGraph.getCollapsedSize and reads the ynode directly via
layoutStore.getNodeCollapsedSize, bypassing NodeLayout entirely.

With the per-frame cache removed in 2693ec256, there is also no longer
any reason to expose the value on NodeLayout as a feeder for a future
reactive-ref-based cache (Y.Map.get is O(1) and not a bottleneck).

Treat this as undoing an unneeded addition from this PR rather than
introducing new indirection:
- Remove collapsedSize from NodeLayout (types.ts).
- Drop the dead conditional write in layoutToYNode and the
  special-case tail in yNodeToLayout — mappers.ts is now identical to
  main.
- layoutStore.updateNodeCollapsedSize / getNodeCollapsedSize /
  clearNodeCollapsedSize keep writing and reading collapsedSize on
  the ynode via Y.Map's string-keyed API.

src/renderer/core/layout/store/layoutStore.ts

@@ -242,7 +242,8 @@ class LayoutStoreImpl implements LayoutStore {
           get: () => {
             track()
             const ynode = this.ynodes.get(nodeId)
-            return ynode ? yNodeToLayout(ynode) : null
+            const layout = ynode ? yNodeToLayout(ynode) : null
+            return layout
           },
           set: (newLayout: NodeLayout | null) => {
             if (newLayout === null) {

src/renderer/core/layout/types.ts

@@ -50,9 +50,6 @@ export interface NodeLayout {
   visible: boolean
   // Computed bounds for hit testing
   bounds: Bounds
-  // Collapsed node dimensions (Vue mode only, separate from size to
-  // preserve expanded size across collapse/expand cycles)
-  collapsedSize?: Size
 }
 
 export interface SlotLayout {

src/renderer/core/layout/utils/mappers.ts

@@ -21,7 +21,6 @@ export function layoutToYNode(layout: NodeLayout): NodeLayoutMap {
   ynode.set('zIndex', layout.zIndex)
   ynode.set('visible', layout.visible)
   ynode.set('bounds', layout.bounds)
-  if (layout.collapsedSize) ynode.set('collapsedSize', layout.collapsedSize)
   return ynode
 }
 
@@ -35,7 +34,7 @@ function getOr<K extends keyof NodeLayout>(
 }
 
 export function yNodeToLayout(ynode: NodeLayoutMap): NodeLayout {
-  const layout: NodeLayout = {
+  return {
     id: getOr(ynode, 'id', NODE_LAYOUT_DEFAULTS.id),
     position: getOr(ynode, 'position', NODE_LAYOUT_DEFAULTS.position),
     size: getOr(ynode, 'size', NODE_LAYOUT_DEFAULTS.size),
@@ -43,8 +42,4 @@ export function yNodeToLayout(ynode: NodeLayoutMap): NodeLayout {
     visible: getOr(ynode, 'visible', NODE_LAYOUT_DEFAULTS.visible),
     bounds: getOr(ynode, 'bounds', NODE_LAYOUT_DEFAULTS.bounds)
   }
-  const collapsedSize = ynode.get('collapsedSize')
-  if (collapsedSize)
-    layout.collapsedSize = collapsedSize as NodeLayout['collapsedSize']
-  return layout
 }