diff --git a/docs/web-cad-implementation-plan.zh-CN.md b/docs/web-cad-implementation-plan.zh-CN.md
index 1c60e8d..2c74a8f 100644
--- a/docs/web-cad-implementation-plan.zh-CN.md
+++ b/docs/web-cad-implementation-plan.zh-CN.md
@@ -1547,7 +1547,8 @@ P0 基线/治理
 3. `P1-01`：建立 `BitBybitWebCadFacade` 最小 TypeScript 合同，只包含 app.document、gui.workbench、gui.command、selection 和 task。
 4. `P1-05`：把当前静态回调替换为 `MockFacadeAdapter`，验证页面不直接修改模型树或属性。
 5. `P1-06`：加入 Facade-only 依赖检查和 CI 失败示例。
-6. `P8-01`：为新建文档、工作台切换、选择 Pad、打开 Task Dock 和属性编辑建立第一批自动化场景。
+6. `P4-01/P4-04`：验证最小 Document/Object 投影、特征追加、事务版本和撤销/重做边界。
+7. `P8-01`：为新建文档、工作台切换、选择 Pad、打开 Task Dock、特征提交和属性编辑建立第一批自动化场景。
 
 迭代退出条件：`npm run build`、类型检查、Facade-only 架构检查和桌面/移动页面截图全部通过；提交信息必须包含任务 ID，例如 `P1-01: define facade contract`。
 
@@ -1588,7 +1589,8 @@ P0 基线/治理
 | P1-03 请求上下文、事件和诊断 | `DONE` | 命令事件携带 API 版本、请求 ID、文档 ID/版本和工作台；禁用命令生成结构化诊断 |
 | P1-05 MockFacadeAdapter | `DONE` | `src/facade/mockFacade.ts`，React 工作区已通过事件投影工作台、选择、文档树和通知 |
 | P1-06 Facade-only 依赖守卫 | `DONE` | `scripts/check-facade-boundary.mjs`，禁止 UI 绕过入口导入 Three.js/SQLite/OPFS/Worker |
+| P4-01/P4-04 Document/Object 与事务最小切片 | `IN PROGRESS` | Pad/Pocket/Fillet/Chamfer 等已通过 Task 确认追加到 Body；文档版本、dirty 标志和 Undo/Redo 已接通，完整属性、依赖 DAG 和重计算仍待实现 |
 | P5-01 Three.js 视口适配器 | `IN PROGRESS` | `src/facade/threeViewport.ts` 使用 `three@0.185.1`，已挂载 WebGL2 场景和资源释放 |
-| P8-01 第一批自动化场景 | `IN PROGRESS` | `tests/facade.test.ts` 已覆盖初始化、事件、任务生命周期、禁用命令和请求上下文；E2E/黄金几何待补齐 |
+| P8-01 第一批自动化场景 | `IN PROGRESS` | `tests/facade.test.ts` 已覆盖初始化、事件、任务生命周期、禁用命令、请求上下文、特征提交和历史；E2E/黄金几何待补齐 |
 
-本迭代验证命令：`npm run check:facade-boundary`、`npm run test:facade`、`npm run build`。构建产物将 Three.js 拆为独立 chunk，避免把全部渲染库重复打入应用主 chunk。下一迭代继续完成 P0-01/P0-02 的精确锁定和 P1-02/P1-03 的命令状态、事件及诊断协议。
+本迭代验证命令：`npm run check:facade-boundary`、`npm run test:facade`、`npm run build`。构建产物将 Three.js 拆为独立 chunk，避免把全部渲染库重复打入应用主 chunk。当前 npm registry 的 `three` 最新版本为 `0.185.1`，已在 `package.json` 和运行时基线中锁定。下一迭代继续完成 P0-01/P0-02 的精确锁定、P2-01/P2-02 的 SQLite/OPFS schema 与 Worker 单写者实验，以及 P3-01 的 FreeCAD/OCCT WASM 构建验证。
diff --git a/src/facade/mockFacade.ts b/src/facade/mockFacade.ts
index 3fe3f49..8cc1188 100644
--- a/src/facade/mockFacade.ts
+++ b/src/facade/mockFacade.ts
@@ -31,6 +31,14 @@ const createDocument = (label = 'Pump Housing'): DocumentSnapshot => ({
 
 const selectionRequired = new Set(['pad', 'pocket', 'revolution', 'fillet', 'chamfer', 'hole', 'linear-pattern', 'polar-pattern', 'measure-distance', 'measure-angle', 'measure-area'])
 const systemCommands = new Set(['new-document', 'save', 'select-object'])
+const featureCommands: Record<string, { label: string; detail: string }> = {
+  'create-body': { label: 'Body', detail: 'Part Design body' },
+  'create-sketch': { label: 'Sketch', detail: 'Fully constrained' },
+  pad: { label: 'Pad', detail: 'Length 42 mm' },
+  pocket: { label: 'Pocket', detail: 'Through all' },
+  fillet: { label: 'Fillet', detail: 'Radius 3 mm' },
+  chamfer: { label: 'Chamfer', detail: 'Length 2 mm' },
+}
 
 const commandState = (commandId: string, activeWorkbench: WorkbenchId, selectedObjectId: string): CommandState => {
   const known = systemCommands.has(commandId) || Object.values(workbenchDefinitions).some((definition) => definition.groups.some((group) => group.commands.some((command) => command.id === commandId)))
@@ -55,6 +63,38 @@ export function createMockFacade(): BitBybitWebCadFacade {
   const setActive = (id: WorkbenchId) => { state = { ...state, activeWorkbench: id }; emitState(); notify(`${id} workbench loaded`) }
   const select = (objectId: string) => { state = { ...state, selectedObjectId: objectId }; emitState() }
   const beginTask = (commandId: string, draft: Record<string, unknown> = {}) => { const task: TaskSnapshot = { id: `task-${++requestSequence}`, commandId, title: workbenchDefinitions[state.activeWorkbench].taskTitle, status: 'preview', draft }; state = { ...state, task }; emitState(); return task }
+  const nextFeatureId = (label: string) => {
+    const base = label.toLowerCase()
+    const existing = state.document.tree.filter((item) => item.label.toLowerCase().startsWith(base)).length
+    return existing === 0 ? base : `${base}${String(existing).padStart(3, '0')}`
+  }
+  const appendFeature = (document: DocumentSnapshot, commandId: string): { document: DocumentSnapshot; objectId: string } => {
+    const definition = featureCommands[commandId]
+    if (!definition) return { document, objectId: '' }
+    const objectId = nextFeatureId(definition.label)
+    const type = commandId === 'create-sketch' ? 'sketch' : commandId === 'create-body' ? 'body' : 'feature'
+    const item: ModelTreeItem = { id: objectId, label: definition.label, type, state: type === 'body' ? 'active' : 'valid', detail: definition.detail }
+    const tree: ModelTreeItem[] = document.tree.map((entry) => ({ ...entry, children: entry.children ? [...entry.children] : undefined }))
+    if (type === 'body') tree.push({ ...item, children: [] })
+    else {
+      const body = tree.find((entry) => entry.type === 'body')
+      if (body) body.children = [...(body.children || []), objectId]
+      tree.push(item)
+    }
+    return { document: { ...document, version: document.version + 1, dirty: true, tree }, objectId }
+  }
+  const applyTask = () => {
+    const task = state.task
+    if (!task || task.status !== 'preview') return
+    const result = appendFeature(state.document, task.commandId)
+    if (!result.objectId) {
+      state = { ...state, task: { ...task, status: 'completed' } }
+      emitState()
+      return
+    }
+    commit({ ...state, document: result.document, selectedObjectId: result.objectId, task: { ...task, status: 'completed' } })
+    notify(`${featureCommands[task.commandId].label} created`)
+  }
   const execute = ({ commandId, payload }: ExecuteCommandInput) => {
     const requestId = `req-${++requestSequence}`
     const context: FacadeRequestContext = { apiVersion: state.apiVersion, requestId, documentId: state.document.id, documentVersion: state.document.version, workbench: state.activeWorkbench }
@@ -68,8 +108,7 @@ export function createMockFacade(): BitBybitWebCadFacade {
     if (commandId === 'new-document') commit({ ...state, document: createDocument('Untitled document'), selectedObjectId: '' })
     else if (commandId === 'save') commit({ ...state, document: { ...state.document, dirty: false, version: state.document.version + 1 } })
     else if (commandId === 'select-object' && typeof payload?.objectId === 'string') select(payload.objectId)
-    else if (commandId === 'create-body') beginTask('create-body')
-    else if (commandId === 'create-sketch') beginTask('create-sketch')
+    else if (featureCommands[commandId]) beginTask(commandId, { source: state.selectedObjectId || null })
     emit({ type: 'command.completed', commandId, context }); emitState(); return requestId
   }
 
@@ -78,7 +117,7 @@ export function createMockFacade(): BitBybitWebCadFacade {
     history: { canUndo: () => undoStack.length > 0, canRedo: () => redoStack.length > 0, undo: () => { const previous = undoStack.pop(); if (!previous) return; redoStack.push(getState()); state = previous; emitState(); notify('Undo applied') }, redo: () => { const next = redoStack.pop(); if (!next) return; undoStack.push(getState()); state = next; emitState(); notify('Redo applied') } },
     gui: { workbench: { list: () => Object.keys(workbenchDefinitions) as WorkbenchId[], getActive: () => state.activeWorkbench, setActive }, command: { getState: (commandId) => commandState(commandId, state.activeWorkbench, state.selectedObjectId), list: (workbench) => workbenchDefinitions[workbench].groups.flatMap((group) => group.commands), execute } },
     selection: { getObjectId: () => state.selectedObjectId, select, clear: () => select('') },
-    task: { getActive: () => getState().task, begin: beginTask, update: (draft) => { if (state.task) state = { ...state, task: { ...state.task, draft: { ...state.task.draft, ...draft } } }; emitState() }, apply: () => { if (state.task) state = { ...state, task: { ...state.task, status: 'completed' } }; emitState() }, cancel: () => { if (state.task) state = { ...state, task: { ...state.task, status: 'cancelled' } }; emitState() } },
+    task: { getActive: () => getState().task, begin: beginTask, update: (draft) => { if (state.task) state = { ...state, task: { ...state.task, draft: { ...state.task.draft, ...draft } } }; emitState() }, apply: applyTask, cancel: () => { if (state.task) state = { ...state, task: { ...state.task, status: 'cancelled' } }; emitState() } },
     viewport: { createAdapter: () => new ThreeViewportAdapter() },
     getState, subscribe: (listener) => { listeners.add(listener); return () => { listeners.delete(listener) } }, notify,
   }
diff --git a/tests/facade.test.ts b/tests/facade.test.ts
index 45ffdfb..ff39346 100644
--- a/tests/facade.test.ts
+++ b/tests/facade.test.ts
@@ -71,3 +71,24 @@ test('document mutations use the facade history boundary', () => {
   facade.history.redo()
   assert.equal(facade.app.document.getActive().label, 'Untitled document')
 })
+
+test('Part Design feature tasks commit a document object and remain undoable', () => {
+  const facade = createMockFacade()
+  const before = facade.app.document.getActive()
+  facade.gui.command.execute({ commandId: 'pad' })
+  assert.equal(facade.task.getActive()?.commandId, 'pad')
+  facade.task.update({ length: 42, reversed: false })
+  facade.task.apply()
+
+  const committed = facade.app.document.getActive()
+  const created = committed.tree.find((item) => item.id === 'pad001')
+  assert.equal(created?.label, 'Pad')
+  assert.equal(committed.version, before.version + 1)
+  assert.equal(facade.selection.getObjectId(), 'pad001')
+  assert.equal(committed.dirty, true)
+
+  facade.history.undo()
+  assert.equal(facade.app.document.getActive().tree.some((item) => item.id === 'pad001'), false)
+  facade.history.redo()
+  assert.equal(facade.app.document.getActive().tree.some((item) => item.id === 'pad001'), true)
+})