diff --git a/B07_DesignDetail/openwebcad/src/helpers/undo-stack.ts b/B07_DesignDetail/openwebcad/src/helpers/undo-stack.ts
index dbbe75cd1..c2240f779 100644
--- a/B07_DesignDetail/openwebcad/src/helpers/undo-stack.ts
+++ b/B07_DesignDetail/openwebcad/src/helpers/undo-stack.ts
@@ -1,8 +1,18 @@
+import type { Layer } from '../App.types';
+
+/** 도면층 목록 + 현재 층 — LAYMRG · LAYDEL 이 객체 변경과 함께 담는다 */
+export interface LayerSnapshot {
+	layers: Layer[];
+	activeLayerId: string;
+}
+
 export interface UndoState {
 	variable: StateVariable;
 
 	// biome-ignore lint/suspicious/noExplicitAny: TODO list all undo state types
 	value: any;
+	/** 이 단계가 도면층도 바꿨다면 전 · 후 — 되돌리면 before · 다시 하면 after 를 복원 */
+	layerChange?: { before: LayerSnapshot; after: LayerSnapshot };
 }
 
 export enum StateVariable {
diff --git a/B07_DesignDetail/openwebcad/src/state.ts b/B07_DesignDetail/openwebcad/src/state.ts
index ad64ff267..57e005795 100644
--- a/B07_DesignDetail/openwebcad/src/state.ts
+++ b/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);
 }
diff --git a/B07_DesignDetail/openwebcad/src/tools/utility/layer-tools.test.ts b/B07_DesignDetail/openwebcad/src/tools/utility/layer-tools.test.ts
new file mode 100644
index 000000000..75d042686
--- /dev/null
+++ b/B07_DesignDetail/openwebcad/src/tools/utility/layer-tools.test.ts
@@ -0,0 +1,88 @@
+import { Point } from '@flatten-js/core';
+import { beforeAll, describe, expect, it } from 'vitest';
+import { createActor } from 'xstate';
+import type { Layer } from '../../App.types';
+import { LineEntity } from '../../entities/LineEntity.ts';
+import {
+	getActiveLayerId,
+	getEntities,
+	getLayers,
+	redo,
+	resetUndoBaseline,
+	setActiveLayerId,
+	setEntities,
+	setLayers,
+	setScreenCanvasDrawController,
+	undo,
+} from '../../state.ts';
+import { ActorEvent } from '../tool.types.ts';
+import { layerDeleteToolStateMachine, layerMergeToolStateMachine } from './layer-tools.ts';
+
+const layer = (id: string): Layer => ({ id, name: id, isVisible: true, isLocked: false });
+
+/** 선 A(레이어 A · y=0) · 선 B(레이어 B · y=100) — 활성층은 A */
+function setup() {
+	const a = new LineEntity('A', new Point(0, 0), new Point(10, 0));
+	const b = new LineEntity('B', new Point(0, 100), new Point(10, 100));
+	setLayers([layer('A'), layer('B')]);
+	setActiveLayerId('A');
+	setEntities([a, b]);
+	resetUndoBaseline();
+}
+
+const click = (actor: ReturnType<typeof createActor>, y: number) =>
+	actor.send({
+		type: ActorEvent.MOUSE_CLICK,
+		worldMouseLocation: new Point(5, y),
+		screenMouseLocation: new Point(0, 0),
+		holdingCtrl: false,
+		holdingShift: false,
+	});
+
+const layerOfEntities = () => getEntities().map((entity) => entity.layerId);
+const layerIds = () => getLayers().map((l) => l.id);
+
+describe('LAYMRG · LAYDEL 되돌리기 (508-3a)', () => {
+	beforeAll(() => {
+		(globalThis as { window?: unknown }).window = { dispatchEvent: () => true };
+		// 집기 반경만 필요 — 화면 배율 1
+		setScreenCanvasDrawController({ getScreenScale: () => 1, getWorldMouseLocation: () => new Point(0, 0) } as never);
+	});
+
+	it('LAYMRG A→B: Ctrl+Z 한 번에 도형 레이어 · 레이어 목록 · 현재 층이 처음대로, Ctrl+Y 로 다시 합쳐짐', () => {
+		setup();
+		const actor = createActor(layerMergeToolStateMachine).start();
+		click(actor, 0);
+		click(actor, 100);
+		expect(layerOfEntities()).toEqual(['B', 'B']);
+		expect(layerIds()).toEqual(['B']);
+		expect(getActiveLayerId()).toBe('B');
+
+		undo();
+		expect(layerOfEntities()).toEqual(['A', 'B']);
+		expect(layerIds()).toEqual(['A', 'B']);
+		expect(getActiveLayerId()).toBe('A');
+
+		redo();
+		expect(layerOfEntities()).toEqual(['B', 'B']);
+		expect(layerIds()).toEqual(['B']);
+		expect(getActiveLayerId()).toBe('B');
+	});
+
+	it('LAYDEL A: Ctrl+Z 한 번에 지운 도형 · 레이어 A 가 돌아오고, Ctrl+Y 로 다시 지워짐', () => {
+		setup();
+		const actor = createActor(layerDeleteToolStateMachine).start();
+		click(actor, 0);
+		expect(layerOfEntities()).toEqual(['B']);
+		expect(layerIds()).toEqual(['B']);
+
+		undo();
+		expect(layerOfEntities()).toEqual(['A', 'B']);
+		expect(layerIds()).toEqual(['A', 'B']);
+		expect(getActiveLayerId()).toBe('A');
+
+		redo();
+		expect(layerOfEntities()).toEqual(['B']);
+		expect(layerIds()).toEqual(['B']);
+	});
+});
diff --git a/B07_DesignDetail/openwebcad/src/tools/utility/layer-tools.ts b/B07_DesignDetail/openwebcad/src/tools/utility/layer-tools.ts
index e80a22ae0..6fd8c7b81 100644
--- a/B07_DesignDetail/openwebcad/src/tools/utility/layer-tools.ts
+++ b/B07_DesignDetail/openwebcad/src/tools/utility/layer-tools.ts
@@ -11,9 +11,11 @@ import {
 	saveLayerState,
 } from '../../helpers/layer-history';
 import {
+	attachLayerChangeToUndo,
 	deleteEntities,
 	getActiveLayerId,
 	getEntities,
+	getLayerSnapshot,
 	getLayers,
 	setActiveLayerId,
 	setLayers,
@@ -29,6 +31,13 @@ function updateLayers(mutate: (layers: Layer[]) => Layer[]): void {
 	setLayers(mutate(current.map((layer) => ({ ...layer }))));
 }
 
+/** 객체 변경 + 도면층 변경을 되돌리기 한 단계로 묶는다(Ctrl+Z 한 번에 함께 · Ctrl+Y 도 짝) */
+function withLayerUndo(change: () => void): void {
+	const before = getLayerSnapshot();
+	change();
+	attachLayerChangeToUndo(before, getLayerSnapshot());
+}
+
 const layerNameOf = (layerId: string): string =>
 	getLayers().find((layer) => layer.id === layerId)?.name ?? layerId;
 
@@ -222,15 +231,17 @@ export const layerMergeToolStateMachine = createSequenceTool({
 			toast.warn('같은 레이어입니다.');
 			return;
 		}
-		// 사본으로 갈아 끼움(제자리 고침 = 되돌리기 칸이 같은 참조 → Ctrl+Z 해도 그대로) · 층 목록 = LAYERP
-		restyle(
-			getEntities().filter((entity) => entity.layerId === sourceId),
-			(entity) => {
-				entity.layerId = targetId;
-			}
-		);
-		updateLayers((layers) => layers.filter((layer) => layer.id !== sourceId));
-		if (getActiveLayerId() === sourceId) setActiveLayerId(targetId);
+		// 사본으로 갈아 끼움(제자리 고침 = 되돌리기 칸이 같은 참조 → Ctrl+Z 해도 그대로)
+		withLayerUndo(() => {
+			restyle(
+				getEntities().filter((entity) => entity.layerId === sourceId),
+				(entity) => {
+					entity.layerId = targetId;
+				}
+			);
+			updateLayers((layers) => layers.filter((layer) => layer.id !== sourceId));
+			if (getActiveLayerId() === sourceId) setActiveLayerId(targetId);
+		});
 		toast.success(`레이어를 ${layerNameOf(targetId)}(으)로 병합했습니다.`);
 	},
 });
@@ -246,9 +257,11 @@ export const layerDeleteToolStateMachine = createSequenceTool({
 			return;
 		}
 		const doomed: Entity[] = getEntities().filter((entity) => entity.layerId === layerId);
-		deleteEntities(doomed, true);
-		updateLayers((layers) => layers.filter((layer) => layer.id !== layerId));
-		if (getActiveLayerId() === layerId) setActiveLayerId(getLayers()[0].id);
+		withLayerUndo(() => {
+			deleteEntities(doomed, true);
+			updateLayers((layers) => layers.filter((layer) => layer.id !== layerId));
+			if (getActiveLayerId() === layerId) setActiveLayerId(getLayers()[0].id);
+		});
 		toast.success(`레이어와 객체 ${doomed.length}개를 삭제했습니다.`);
 	},
 });