feat(508-3a CAD 레이어 합치기 되돌리기): LAYMRG · LAYDEL 뒤 Ctrl+Z 한 번에 도형 레이어 · 레이어 목록 · 현재 층이 함께 돌아오고 Ctrl+Y 도 짝 · 되돌리기 단계에 도면층 전후 담음(state attachLayerChangeToUndo) · vitest layer-tools.test · 요구 325-1

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

B07_DesignDetail/openwebcad/src/state.ts

@@ -12,7 +12,12 @@ import {
 import type { ScreenCanvasDrawController } from './drawControllers/screenCanvas.drawController';
 import type { Entity } from './entities/Entity';
 import { bumpSceneVersion } from './helpers/scene-version';
-import { StateVariable, type UndoState, createStack } from './helpers/undo-stack';
+import {
+	type LayerSnapshot,
+	StateVariable,
+	type UndoState,
+	createStack,
+} from './helpers/undo-stack';
 import type { InputController } from './inputController/input-controller.ts'; // state variables
 import { type PromptMeta, renderPrompt, rememberPoint, resolvePrompt } from './commands/prompt';
 
@@ -626,20 +631,43 @@ export function resetUndoBaseline() {
 	drawingDirty = false;
 }
 
+export const getLayerSnapshot = (): LayerSnapshot => ({ layers, activeLayerId });
+
+/**
+ * 방금 쌓은 객체 되돌리기 단계에 도면층 전 · 후를 붙인다(LAYMRG · LAYDEL) —
+ * Ctrl+Z 한 번에 객체와 도면층이 함께 돌아오고 Ctrl+Y 도 짝으로 간다.
+ * 맨 위 단계가 지금 객체 목록이 아니면(쌓이지 않음) 붙이지 않는다.
+ */
+export function attachLayerChangeToUndo(before: LayerSnapshot, after: LayerSnapshot) {
+	const top = undoStack.peek();
+	if (top?.variable === StateVariable.entities && top.value === entities) {
+		top.layerChange = { before, after };
+	}
+}
+
+function applyLayerSnapshot(snapshot: LayerSnapshot) {
+	setLayers(snapshot.layers);
+	setActiveLayerId(snapshot.activeLayerId);
+}
+
 export function undo() {
+	const undone = undoStack.peek();
 	const undoState = undoStack.undo();
 	if (!undoState) return;
 
 	updateStates(undoState);
+	if (undone !== undoState && undone?.layerChange) applyLayerSnapshot(undone.layerChange.before);
 	drawingDirty = true; // 되돌려도 저장본과는 다를 수 있다 — 미저장 경고 대상이다
 	notifyWindow(HtmlEvent.DRAWING_CHANGED);
 }
 
 export function redo() {
+	const current = undoStack.peek();
 	const redoState = undoStack.redo();
 	if (!redoState) return;
 
 	updateStates(redoState);
+	if (current !== redoState && redoState.layerChange) applyLayerSnapshot(redoState.layerChange.after);
 	drawingDirty = true;
 	notifyWindow(HtmlEvent.DRAWING_CHANGED);
 }