fix: preserve canvas receiver when invoking deferred onSelectionChange

Synchronous callsites use this.onSelectionChange?.(...) which binds the
LGraphCanvas instance as the callback's receiver. The deferred RAF
invocation called the saved reference as a bare function, so this would
be undefined inside the callback under strict mode — silently changing
the contract for an extension-facing callback only on the drag-start
path.

Use Function.prototype.call so the deferred invocation matches every
other onSelectionChange call in the file.

Adds a test that pins the receiver contract.

src/lib/litegraph/src/LGraphCanvas.dragStartDeferral.test.ts

@@ -132,6 +132,18 @@ describe('_startDraggingItems defers onSelectionChange', () => {
     expect(onSelectionChange).not.toHaveBeenCalled()
   })
 
+  it('invokes the deferred onSelectionChange with the canvas as receiver', () => {
+    const receivedThis: unknown[] = []
+    canvas.onSelectionChange = function (this: unknown) {
+      receivedThis.push(this)
+    }
+
+    canvas['_startDraggingItems'](node, pointer, true)
+    vi.advanceTimersByTime(16)
+
+    expect(receivedThis).toEqual([canvas])
+  })
+
   it('restores onSelectionChange even when processSelect throws', () => {
     const onSelectionChange = vi.fn()
     canvas.onSelectionChange = onSelectionChange

src/lib/litegraph/src/LGraphCanvas.ts

@@ -3629,7 +3629,9 @@ export class LGraphCanvas implements CustomEventDispatcher<LGraphCanvasEventMap>
       this.onSelectionChange = onSelectionChange
     }
     if (onSelectionChange && selectionNotified) {
-      requestAnimationFrame(() => onSelectionChange(this.selected_nodes))
+      requestAnimationFrame(() => {
+        onSelectionChange.call(this, this.selected_nodes)
+      })
     }
 
     this.isDragging = true