diff --git a/B07_DesignDetail/openwebcad/src/drawControllers/screenCanvas.drawController.ts b/B07_DesignDetail/openwebcad/src/drawControllers/screenCanvas.drawController.ts
index 753a1803..f37b3199 100644
--- a/B07_DesignDetail/openwebcad/src/drawControllers/screenCanvas.drawController.ts
+++ b/B07_DesignDetail/openwebcad/src/drawControllers/screenCanvas.drawController.ts
@@ -69,7 +69,6 @@ export class ScreenCanvasDrawController implements DrawController {
 	}
 
 	public setScreenScale(newScreenScale: number) {
-		console.log(`set screen scale: ${newScreenScale}`);
 		this.screenScale = newScreenScale;
 		triggerReactUpdate(StateVariable.screenZoom);
 	}
diff --git a/B07_DesignDetail/openwebcad/src/entities/Entity.ts b/B07_DesignDetail/openwebcad/src/entities/Entity.ts
index 23dc7403..135f4be9 100644
--- a/B07_DesignDetail/openwebcad/src/entities/Entity.ts
+++ b/B07_DesignDetail/openwebcad/src/entities/Entity.ts
@@ -86,6 +86,8 @@ export interface JsonEntity<TShapeJsonData = ShapeJsonData> {
 	lineWidth: number;
 	lineDash?: number[];
 	layerId: string;
+	/** GROUP 묶음 식별자 — 저장·복원에서 그대로 실어 나른다 */
+	groupId?: string;
 	shapeData: TShapeJsonData | null;
 	children?: JsonEntity<ShapeJsonData>[];
 }
diff --git a/B07_DesignDetail/openwebcad/src/helpers/import-export-handlers/export-entities-to-json.ts b/B07_DesignDetail/openwebcad/src/helpers/import-export-handlers/export-entities-to-json.ts
index d33f56c1..b0d59331 100644
--- a/B07_DesignDetail/openwebcad/src/helpers/import-export-handlers/export-entities-to-json.ts
+++ b/B07_DesignDetail/openwebcad/src/helpers/import-export-handlers/export-entities-to-json.ts
@@ -14,7 +14,11 @@ export async function exportEntitiesToJsonFile() {
 export async function exportEntitiesAndLayersToJsonString() {
 	const entities = getEntities();
 
-	const jsonEntities = entities.map((entity) => entity.toJson());
+	// groupId는 엔티티 13종의 toJson을 다 고치는 대신 여기 한 곳에서 붙인다.
+	const jsonEntities = entities.map(async (entity) => {
+		const json = await entity.toJson();
+		return json && entity.groupId ? { ...json, groupId: entity.groupId } : json;
+	});
 	const jsonDrawingFile: JsonDrawingFileSerialized = {
 		entities: compact(await Promise.all(jsonEntities)), // TODO use a mapLimit to avoid overloading the event loop
 		layers: getLayers(),
diff --git a/B07_DesignDetail/openwebcad/src/helpers/import-export-handlers/group-id-roundtrip.test.ts b/B07_DesignDetail/openwebcad/src/helpers/import-export-handlers/group-id-roundtrip.test.ts
new file mode 100644
index 00000000..d0ee722c
--- /dev/null
+++ b/B07_DesignDetail/openwebcad/src/helpers/import-export-handlers/group-id-roundtrip.test.ts
@@ -0,0 +1,30 @@
+import { Point } from '@flatten-js/core';
+import { describe, expect, it } from 'vitest';
+import { LineEntity } from '../../entities/LineEntity.ts';
+import { setEntities, setLayers } from '../../state.ts';
+import { exportEntitiesAndLayersToJsonString } from './export-entities-to-json.ts';
+import { getEntitiesAndLayersFromJsonString } from './import-entities-from-json.ts';
+
+describe('groupId 저장·복원', () => {
+	it('GROUP 묶음이 JSON 왕복 뒤에도 한 덩어리로 남는다', async () => {
+		const layer = { id: 'layer-1', isLocked: false, isVisible: true, name: '작업' };
+		const groupId = 'group-1';
+		const first = new LineEntity(layer.id, new Point(0, 0), new Point(1, 0));
+		const second = new LineEntity(layer.id, new Point(1, 0), new Point(1, 1));
+		const loner = new LineEntity(layer.id, new Point(2, 2), new Point(3, 3));
+		first.groupId = groupId;
+		second.groupId = groupId;
+
+		setLayers([layer]);
+		setEntities([first, second, loner]);
+
+		const restored = await getEntitiesAndLayersFromJsonString(
+			await exportEntitiesAndLayersToJsonString()
+		);
+		const byId = new Map(restored.entities.map((entity) => [entity.id, entity]));
+
+		expect(byId.get(first.id)?.groupId).toBe(groupId);
+		expect(byId.get(second.id)?.groupId).toBe(groupId);
+		expect(byId.get(loner.id)?.groupId).toBeUndefined();
+	});
+});
diff --git a/B07_DesignDetail/openwebcad/src/helpers/import-export-handlers/import-entities-from-json.ts b/B07_DesignDetail/openwebcad/src/helpers/import-export-handlers/import-entities-from-json.ts
index c121cf78..6cfbf049 100644
--- a/B07_DesignDetail/openwebcad/src/helpers/import-export-handlers/import-entities-from-json.ts
+++ b/B07_DesignDetail/openwebcad/src/helpers/import-export-handlers/import-entities-from-json.ts
@@ -77,6 +77,12 @@ export async function getEntitiesAndLayersFromJsonObject(
 	);
 
 	const entities = compact(await Promise.all(entityPromises));
+	// 순번이 아니라 id로 되돌린다 — compact가 null을 걷어 index가 어긋날 수 있다.
+	const groupIdById = new Map(data.entities.map((entity) => [entity.id, entity.groupId]));
+	for (const entity of entities) {
+		const groupId = groupIdById.get(entity.id);
+		if (groupId) entity.groupId = groupId;
+	}
 	let layers = data.layers;
 	if (data.layers.length === 0) {
 		layers = [getNewLayer()];