diff --git a/Makefile b/Makefile
index 441d684..83679b0 100644
--- a/Makefile
+++ b/Makefile
@@ -43,6 +43,7 @@ check-frontend:
 	cd frontend && $(PNPM) lint
 	cd frontend && $(PNPM) format:check
 	cd frontend && $(PNPM) typecheck
+	cd frontend && $(PNPM) test
 	cd frontend && $(PNPM) build
 
 contracts:
diff --git a/frontend/README.md b/frontend/README.md
index 19dc9a2..3cc7779 100644
--- a/frontend/README.md
+++ b/frontend/README.md
@@ -7,6 +7,7 @@ Vue 3 + TypeScript + Vite + Element Plus，使用 Vue Router 与 Pinia。
 pnpm install --frozen-lockfile
 pnpm dev
 pnpm typecheck
+pnpm test
 pnpm build
 ```
 
@@ -22,3 +23,5 @@ pnpm build
 已有代码按实际需要落位；`components/` 和 `stores/` 是后续扩展位置，不放空状态实现。
 API 类型更新执行根目录 `make contracts`；前端通过 `pnpm check:api` 拒绝过期类型。
 登录凭据、模型密钥和数据库连接不能进入 `VITE_` 环境变量。
+
+`pnpm test` 验证代码草稿在刷新、切到后台与页面离开时的保存行为，已纳入 `make check-frontend`。
diff --git a/frontend/package.json b/frontend/package.json
index 59b7459..58f7e6c 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -12,6 +12,7 @@
     "build": "vue-tsc --noEmit && vite build",
     "preview": "vite preview --host 127.0.0.1",
     "typecheck": "vue-tsc --noEmit",
+    "test": "node --test tests/*.test.ts",
     "lint": "eslint . --max-warnings 0",
     "format": "prettier --write .",
     "format:check": "prettier --check .",
diff --git a/frontend/src/composables/useCodeDraft.ts b/frontend/src/composables/useCodeDraft.ts
index f1ac72a..f1c17c7 100644
--- a/frontend/src/composables/useCodeDraft.ts
+++ b/frontend/src/composables/useCodeDraft.ts
@@ -67,11 +67,22 @@ export function useCodeDraft(problemId: string) {
       clearTimeout(timer)
       timer = setTimeout(save, 400)
     },
-    { deep: true },
+    // Mark pending changes before a lifecycle event can run in the same tick.
+    { deep: true, flush: 'sync' },
   )
-  onScopeDispose(() => {
+  function flushPendingDraft() {
     if (state.value === 'changed') save()
+  }
+  function onVisibilityChange() {
+    if (document.visibilityState === 'hidden') flushPendingDraft()
+  }
+  window.addEventListener('pagehide', flushPendingDraft)
+  document.addEventListener('visibilitychange', onVisibilityChange)
+  onScopeDispose(() => {
+    flushPendingDraft()
     clearTimeout(timer)
+    window.removeEventListener('pagehide', flushPendingDraft)
+    document.removeEventListener('visibilitychange', onVisibilityChange)
   })
   return { language, code, state, save }
 }
diff --git a/frontend/tests/useCodeDraft.test.ts b/frontend/tests/useCodeDraft.test.ts
new file mode 100644
index 0000000..b2cc75a
--- /dev/null
+++ b/frontend/tests/useCodeDraft.test.ts
@@ -0,0 +1,164 @@
+import assert from 'node:assert/strict'
+import { test, type TestContext } from 'node:test'
+import { effectScope, nextTick } from 'vue'
+import { codeTemplates, useCodeDraft, type Language } from '../src/composables/useCodeDraft.ts'
+
+type SavedDraft = { version: number; language: Language; drafts: Record<Language, string> }
+
+function browser(t: TestContext) {
+  const page = new EventTarget()
+  const document = Object.assign(new EventTarget(), {
+    visibilityState: 'visible' as DocumentVisibilityState,
+  })
+  const storage = {
+    items: new Map<string, string>(),
+    writes: 0,
+    failWrites: false,
+    getItem(key: string) {
+      return this.items.get(key) ?? null
+    },
+    setItem(key: string, value: string) {
+      this.writes++
+      if (this.failWrites) throw new Error('Storage unavailable')
+      this.items.set(key, value)
+    },
+  }
+  const globals = { window: page, document, localStorage: storage }
+  const descriptors = Object.keys(globals).map(
+    (name) => [name, Object.getOwnPropertyDescriptor(globalThis, name)] as const,
+  )
+  for (const [name, value] of Object.entries(globals)) {
+    Object.defineProperty(globalThis, name, { configurable: true, writable: true, value })
+  }
+  t.mock.timers.enable({ apis: ['setTimeout'] })
+  const scopes: ReturnType<typeof effectScope>[] = []
+  t.after(() => {
+    for (const scope of scopes) scope.stop()
+    for (const [name, descriptor] of descriptors) {
+      if (descriptor) Object.defineProperty(globalThis, name, descriptor)
+      else Reflect.deleteProperty(globalThis, name)
+    }
+  })
+  return {
+    page,
+    document,
+    storage,
+    open(problemId = '1001') {
+      const scope = effectScope()
+      scopes.push(scope)
+      return { scope, ...scope.run(() => useCodeDraft(problemId))! }
+    },
+    read(problemId = '1001'): SavedDraft | null {
+      return JSON.parse(storage.getItem('kf-oj:code-draft:' + problemId) ?? 'null')
+    },
+  }
+}
+
+test('pagehide saves the latest edit before the debounce and restores it after reload', (t) => {
+  const env = browser(t)
+  const draft = env.open()
+  draft.code.value = '// latest edit before refresh'
+  env.page.dispatchEvent(new Event('pagehide'))
+  assert.equal(env.read()?.drafts.cpp, draft.code.value)
+  assert.equal(draft.state.value, 'saved')
+  t.mock.timers.tick(400)
+  assert.equal(env.storage.writes, 1)
+  draft.scope.stop()
+  assert.equal(env.open().code.value, '// latest edit before refresh')
+})
+
+test('hiding the page flushes pending edits; remaining visible does not', async (t) => {
+  const env = browser(t)
+  const draft = env.open()
+  draft.code.value = '// edited while visible'
+  await nextTick()
+  env.document.dispatchEvent(new Event('visibilitychange'))
+  assert.equal(env.storage.writes, 0)
+  env.document.visibilityState = 'hidden'
+  env.document.dispatchEvent(new Event('visibilitychange'))
+  assert.equal(env.read()?.drafts.cpp, draft.code.value)
+  t.mock.timers.tick(400)
+  assert.equal(env.storage.writes, 1)
+})
+
+test('normal typing still debounces writes and saves the most recent edit', async (t) => {
+  const env = browser(t)
+  const draft = env.open()
+  draft.code.value = '// first edit'
+  await nextTick()
+  t.mock.timers.tick(399)
+  assert.equal(env.storage.writes, 0)
+  draft.code.value = '// second edit'
+  await nextTick()
+  t.mock.timers.tick(399)
+  assert.equal(env.storage.writes, 0)
+  t.mock.timers.tick(1)
+  assert.equal(env.read()?.drafts.cpp, '// second edit')
+  assert.equal(env.storage.writes, 1)
+})
+
+test('leaving a Vue page saves even an edit made in the same tick', (t) => {
+  const env = browser(t)
+  const draft = env.open()
+  draft.code.value = '// latest edit before navigation'
+  draft.scope.stop()
+  assert.equal(env.read()?.drafts.cpp, '// latest edit before navigation')
+  t.mock.timers.tick(400)
+  assert.equal(env.storage.writes, 1)
+})
+
+test('disposing the scope removes page lifecycle listeners', (t) => {
+  const env = browser(t)
+  const removePage = t.mock.method(env.page, 'removeEventListener')
+  const removeDocument = t.mock.method(env.document, 'removeEventListener')
+  env.open().scope.stop()
+  assert.deepEqual(
+    removePage.mock.calls.map((call) => call.arguments[0]),
+    ['pagehide'],
+  )
+  assert.deepEqual(
+    removeDocument.mock.calls.map((call) => call.arguments[0]),
+    ['visibilitychange'],
+  )
+  env.page.dispatchEvent(new Event('pagehide'))
+  env.document.visibilityState = 'hidden'
+  env.document.dispatchEvent(new Event('visibilitychange'))
+  assert.equal(env.storage.writes, 0)
+})
+
+test('pagehide preserves the selected language and keeps problem drafts separate', (t) => {
+  const env = browser(t)
+  const first = env.open('1001')
+  first.code.value = '// C++ draft'
+  first.language.value = 'python'
+  first.code.value = '# Python draft'
+  const second = env.open('1002')
+  second.code.value = '// another problem'
+  env.page.dispatchEvent(new Event('pagehide'))
+  assert.deepEqual(env.read('1001'), {
+    version: 1,
+    language: 'python',
+    drafts: { cpp: '// C++ draft', python: '# Python draft', rust: codeTemplates.rust },
+  })
+  assert.equal(env.read('1002')?.drafts.cpp, '// another problem')
+  first.scope.stop()
+  const restored = env.open('1001')
+  assert.equal(restored.language.value, 'python')
+  assert.equal(restored.code.value, '# Python draft')
+})
+
+test('a failed lifecycle save reports unavailable storage without throwing', (t) => {
+  const env = browser(t)
+  const draft = env.open()
+  env.storage.failWrites = true
+  draft.code.value = '// cannot persist yet'
+  assert.doesNotThrow(() => env.page.dispatchEvent(new Event('pagehide')))
+  assert.equal(draft.state.value, 'unavailable')
+  t.mock.timers.tick(400)
+  assert.equal(env.storage.writes, 1)
+  env.storage.failWrites = false
+  draft.code.value = '// storage recovered'
+  env.page.dispatchEvent(new Event('pagehide'))
+  assert.equal(draft.state.value, 'saved')
+  assert.equal(env.read()?.drafts.cpp, '// storage recovered')
+})
diff --git a/frontend/tsconfig.json b/frontend/tsconfig.json
index a216dce..2f52f31 100644
--- a/frontend/tsconfig.json
+++ b/frontend/tsconfig.json
@@ -6,6 +6,7 @@
     "moduleResolution": "Bundler",
     "strict": true,
     "noEmit": true,
+    "allowImportingTsExtensions": true,
     "skipLibCheck": true,
     "esModuleInterop": true,
     "resolveJsonModule": true,
@@ -15,5 +16,5 @@
     "noUnusedParameters": true,
     "types": ["vite/client", "node"]
   },
-  "include": ["src/**/*.ts", "src/**/*.vue", "vite.config.ts"]
+  "include": ["src/**/*.ts", "src/**/*.vue", "tests/**/*.ts", "vite.config.ts"]
 }