diff --git a/admin-frontend-vue/src/layout/AdminLayout.vue b/admin-frontend-vue/src/layout/AdminLayout.vue
index 9519949c..a3ad28ff 100644
--- a/admin-frontend-vue/src/layout/AdminLayout.vue
+++ b/admin-frontend-vue/src/layout/AdminLayout.vue
@@ -12,11 +12,27 @@ import {
   shouldShowEmptyMenu,
 } from '@/layout/empty-state'
 import GlobalErrorContainer from '@/layout/GlobalErrorContainer.vue'
+import { initialCollapsed, toggleCollapsed, writeCollapsePreference } from '@/layout/sidebar-collapse'
 
 const route = useRoute()
 const router = useRouter()
 const session = useAdminSessionStore()
-const collapsed = ref(false)
+const collapsed = ref(readInitialCollapse())
+
+function readInitialCollapse(): boolean {
+  const storage = typeof window !== 'undefined' ? window.localStorage : null
+  const width = typeof window !== 'undefined' ? window.innerWidth : 0
+  return initialCollapsed(width, storage)
+}
+
+function setCollapsed(value: boolean): void {
+  collapsed.value = value
+  if (typeof window !== 'undefined') writeCollapsePreference(window.localStorage, value)
+}
+
+function toggleSidebar(): void {
+  setCollapsed(toggleCollapsed(collapsed.value))
+}
 
 const activePath = computed(() => route.path)
 const menuEntries = computed(() => toSidebarEntries(session.menuTree))
@@ -65,7 +81,7 @@ async function signOut() {
         <el-empty v-if="emptyMenu" :description="EMPTY_MENU_TITLE" :image-size="72" />
       </el-scrollbar>
 
-      <button class="sidebar-collapse" type="button" @click="collapsed = !collapsed">
+      <button class="sidebar-collapse" type="button" @click="toggleSidebar">
         {{ collapsed ? '展开菜单' : '收起菜单' }}
       </button>
     </aside>
diff --git a/admin-frontend-vue/src/layout/sidebar-collapse.ts b/admin-frontend-vue/src/layout/sidebar-collapse.ts
new file mode 100644
index 00000000..03eae78d
--- /dev/null
+++ b/admin-frontend-vue/src/layout/sidebar-collapse.ts
@@ -0,0 +1,56 @@
+/** 侧边栏折叠与窄屏布局状态（任务 14）：宽高常量、阈值、偏好持久化。 */
+
+export const SIDEBAR_EXPANDED_WIDTH = 248
+export const SIDEBAR_COLLAPSED_WIDTH = 64
+export const SIDEBAR_NARROW_THRESHOLD = 900
+
+/** 视口窄到需要自动收起侧边栏。 */
+export function isNarrowScreen(width: number): boolean {
+  return width > 0 && width <= SIDEBAR_NARROW_THRESHOLD
+}
+
+/** 反转折叠状态。 */
+export function toggleCollapsed(current: boolean): boolean {
+  return !current
+}
+
+export type CollapseStorage = Pick<Storage, 'getItem' | 'setItem'> | null
+
+const PREFERENCE_KEY = 'admin.sidebar.collapsed'
+
+function parsePreference(raw: string | null): boolean | null {
+  return raw === 'true' ? true : raw === 'false' ? false : null
+}
+
+/** 读取持久化偏好；无存储或值非法返回 null。 */
+export function readCollapsePreference(storage: CollapseStorage): boolean | null {
+  try {
+    return parsePreference(storage?.getItem(PREFERENCE_KEY) ?? null)
+  } catch {
+    return null
+  }
+}
+
+/** 写入折叠偏好；存储不可用时静默失败（不阻断交互）。 */
+export function writeCollapsePreference(storage: CollapseStorage, collapsed: boolean): void {
+  try {
+    storage?.setItem(PREFERENCE_KEY, String(collapsed))
+  } catch {
+    // localStorage 不可用（隐私模式等）时忽略
+  }
+}
+
+/**
+ * 初始折叠值：优先持久化偏好；无偏好时窄屏自动折叠、宽屏展开。
+ * width<=0（如 SSR/未知）视为无法判定，回退 false。
+ */
+export function initialCollapsed(width: number, storage: CollapseStorage): boolean {
+  const preference = readCollapsePreference(storage)
+  if (preference !== null) return preference
+  return isNarrowScreen(width)
+}
+
+/** 侧边栏应占用的像素宽（用于宽度计算/测试，不直接改 CSS）。 */
+export function sidebarPixelWidth(collapsed: boolean): number {
+  return collapsed ? SIDEBAR_COLLAPSED_WIDTH : SIDEBAR_EXPANDED_WIDTH
+}
diff --git a/admin-frontend-vue/tests/task-14.test.ts b/admin-frontend-vue/tests/task-14.test.ts
new file mode 100644
index 00000000..558dcd22
--- /dev/null
+++ b/admin-frontend-vue/tests/task-14.test.ts
@@ -0,0 +1,93 @@
+import test from 'node:test'
+import assert from 'node:assert/strict'
+import { readSource } from './helpers.ts'
+import {
+  initialCollapsed,
+  isNarrowScreen,
+  readCollapsePreference,
+  SIDEBAR_COLLAPSED_WIDTH,
+  SIDEBAR_EXPANDED_WIDTH,
+  SIDEBAR_NARROW_THRESHOLD,
+  sidebarPixelWidth,
+  toggleCollapsed,
+  writeCollapsePreference,
+  type CollapseStorage,
+} from '../src/layout/sidebar-collapse.ts'
+
+function fakeStorage(entries: Record<string, string>, failing = false): CollapseStorage {
+  return {
+    getItem(key: string) {
+      if (failing) throw new Error('storage down')
+      return key in entries ? entries[key] : null
+    },
+    setItem(key: string, value: string) {
+      if (failing) throw new Error('storage down')
+      entries[key] = value
+    },
+  }
+}
+
+test('test_task_014_sidebar_responsive_behavior_normal_primary_path', () => {
+  // 正常主路径：折叠开关反转状态。
+  assert.equal(toggleCollapsed(false), true)
+  assert.equal(toggleCollapsed(true), false)
+})
+
+test('test_task_014_sidebar_responsive_behavior_normal_variant_input', () => {
+  // 正常变体：不同宽度判定窄屏与宽屏。
+  assert.equal(isNarrowScreen(SIDEBAR_NARROW_THRESHOLD), true)
+  assert.equal(isNarrowScreen(SIDEBAR_NARROW_THRESHOLD + 1), false)
+  assert.equal(isNarrowScreen(1440), false)
+})
+
+test('test_task_014_sidebar_responsive_behavior_normal_repeated_operation_is_idempotent', () => {
+  // 正常重复：偏好读写与宽度结果稳定。
+  const storage = fakeStorage({})
+  assert.equal(initialCollapsed(1000, storage), initialCollapsed(1000, storage))
+  writeCollapsePreference(storage, true)
+  assert.equal(readCollapsePreference(storage), true)
+  assert.equal(readCollapsePreference(storage), true)
+})
+
+test('test_task_014_sidebar_responsive_behavior_boundary_empty_input', () => {
+  // 边界空值：未知宽度/无存储不崩溃且回退展开。
+  assert.equal(isNarrowScreen(0), false)
+  assert.equal(initialCollapsed(0, null), false)
+  assert.equal(readCollapsePreference(null), null)
+})
+
+test('test_task_014_sidebar_responsive_behavior_boundary_single_item', () => {
+  // 边界单元素：单值持久化可读回。
+  const storage = fakeStorage({ 'admin.sidebar.collapsed': 'false' })
+  assert.equal(readCollapsePreference(storage), false)
+  assert.equal(initialCollapsed(1024, storage), false)
+})
+
+test('test_task_014_sidebar_responsive_behavior_boundary_limit_or_missing_field', () => {
+  // 边界上限/缺字段：非法持久化值按无偏好处理；像素宽与常量一致。
+  const storage = fakeStorage({ 'admin.sidebar.collapsed': 'maybe' })
+  assert.equal(readCollapsePreference(storage), null)
+  assert.equal(sidebarPixelWidth(true), SIDEBAR_COLLAPSED_WIDTH)
+  assert.equal(sidebarPixelWidth(false), SIDEBAR_EXPANDED_WIDTH)
+  assert.equal(SIDEBAR_COLLAPSED_WIDTH < SIDEBAR_EXPANDED_WIDTH, true)
+})
+
+test('test_task_014_sidebar_responsive_behavior_invalid_input_rejected', () => {
+  // 异常输入：存储读写失败被容忍，不阻断交互。
+  const broken = fakeStorage({}, true)
+  assert.equal(readCollapsePreference(broken), null)
+  assert.doesNotThrow(() => writeCollapsePreference(broken, true))
+  const fallback = fakeStorage({ 'admin.sidebar.collapsed': 'true' })
+  assert.equal(initialCollapsed(1440, fallback), true, '持久化优先于视口宽度')
+})
+
+test('test_task_014_sidebar_responsive_behavior_dependency_failure_returns_actionable_message', () => {
+  // 依赖失败：壳层接入折叠逻辑；CSS 有 is-collapsed 与窄屏媒体适配。
+  const layout = readSource('src/layout/AdminLayout.vue')
+  assert.match(layout, /initialCollapsed/)
+  assert.match(layout, /writeCollapsePreference/)
+  assert.match(layout, /toggleSidebar/)
+  const css = readSource('src/styles/main.css')
+  assert.match(css, /is-collapsed/)
+  assert.match(css, /@media \(max-width: 820px\)/)
+})