fix(学习会话)：休息倒计时刷新后丢失

根因：休息倒计时完全存在浏览器内存中（runCountdown），
刷新页面后 loadTaskSession() 读取会话为 PAUSED 状态，
走 else 分支 syncDisplay(pointerPosition) 重置为工作钟，
休息状态和剩余时间全部丢失。

修复方案（纯前端）：
- restTimer() 将休息结束时间戳写入 localStorage
- loadTaskSession() 启动时检查 localStorage，
  若休息未到期则恢复 runCountdown 继续倒计时
- startTimer()/stopTimer()/endTimer() 清除休息状态
- 休息期间 UI：倒计时数字橙色、进度环金色、
  按钮区替换为休息中标签（隐藏开始/暂停/残片）

src/components/StartTask.vue

@@ -72,7 +72,15 @@ const {
   requestAudioPermission,
 } = useTimer();
 
-const progress = computed(() => ((timerMinutes.value * 60 + timerSeconds.value) / (25 * 60)) * 100);
+// 休息状态持久化（刷新后恢复）
+const BREAK_END_KEY = computed(() => `breakEnd_${taskNum}`);
+const isBreak = ref(false);
+const breakAudio = new Audio('/resource/notification.mp3');
+
+const progress = computed(() => {
+  const total = isBreak.value ? 5 * 60 : 25 * 60;
+  return ((timerMinutes.value * 60 + timerSeconds.value) / total) * 100;
+});
 const nowTimestamp = ref(Date.now());
 
 let displayInterval: number | undefined;
@@ -170,6 +178,9 @@ const startTimer = async () => {
     if (res.code === 200) ElMessage.success("任务继续");
     await loadTaskSession();
   }
+  // 手动开始 → 清除休息状态
+  localStorage.removeItem(BREAK_END_KEY.value);
+  isBreak.value = false;
   const duration = taskInfo.value.pointerPosition || 25 * 60 * 1000;
   runCountdown(duration);
 };
@@ -181,6 +192,12 @@ const stopTimer = async () => {
     taskInfo.value.sessionState = "PAUSED";
   }
   clear();
+  clearBreakState();
+};
+
+const clearBreakState = () => {
+  localStorage.removeItem(BREAK_END_KEY.value);
+  isBreak.value = false;
 };
 
 const endTimer = async (content: string) => {
@@ -211,6 +228,7 @@ const endTimer = async (content: string) => {
       ElMessage.error(res.message || "结束会话失败");
     }
     clear();
+    clearBreakState();
     await router.push("/study");
   } catch {
     ElMessage.error("结束会话失败，请重试");
@@ -241,7 +259,23 @@ const closeSummaryDialog = () => {
 
 const restTimer = async () => {
   await stopTimer();
-  runCountdown(5 * 60 * 1000);
+  const breakMs = 5 * 60 * 1000;
+  localStorage.setItem(BREAK_END_KEY.value, String(Date.now() + breakMs));
+  isBreak.value = true;
+  runCountdown(breakMs, () => {
+    localStorage.removeItem(BREAK_END_KEY.value);
+    isBreak.value = false;
+    breakAudio.loop = true;
+    breakAudio.play();
+    ElMessageBox.alert('休息结束！点击"开始"继续学习', '休息结束', {
+      confirmButtonText: '关闭铃声',
+      callback: () => {
+        breakAudio.pause();
+        breakAudio.currentTime = 0;
+        ElMessage.success('铃声已关闭');
+      },
+    });
+  });
 };
 
 const loadTaskSession = async () => {
@@ -249,6 +283,34 @@ const loadTaskSession = async () => {
     const res = await startOrContinueStudySession(taskNum);
     Object.assign(taskInfo.value, res.data);
     await loadExpectation();
+
+    // 检查是否有未结束的休息
+    const storedEnd = localStorage.getItem(BREAK_END_KEY.value);
+    if (storedEnd) {
+      const remaining = parseInt(storedEnd, 10) - Date.now();
+      if (remaining > 0) {
+        isBreak.value = true;
+        runCountdown(remaining, () => {
+          localStorage.removeItem(BREAK_END_KEY.value);
+          isBreak.value = false;
+          breakAudio.loop = true;
+          breakAudio.play();
+          ElMessageBox.alert('休息结束！点击"开始"继续学习', '休息结束', {
+            confirmButtonText: '关闭铃声',
+            callback: () => {
+              breakAudio.pause();
+              breakAudio.currentTime = 0;
+              ElMessage.success('铃声已关闭');
+            },
+          });
+        });
+        loadFragments();
+        return;
+      } else {
+        localStorage.removeItem(BREAK_END_KEY.value);
+      }
+    }
+
     if (taskInfo.value.sessionState === "ONGOING") {
       startTimer();
     } else {
@@ -404,13 +466,19 @@ onUnmounted(() => {
 
     <div class="session-grid">
       <article class="surface-card timer-card">
-        <p class="timer-title">当前计时</p>
+        <p class="timer-title">{{ isBreak ? '☕ 休息中' : '当前计时' }}</p>
-        <el-progress type="dashboard" :percentage="progress" :stroke-width="14" :width="250" color="#2f8f68">
+        <el-progress
-          <div class="timer-number">
+          type="dashboard"
+          :percentage="progress"
+          :stroke-width="14"
+          :width="250"
+          :color="isBreak ? '#e6a23c' : '#2f8f68'"
+        >
+          <div class="timer-number" :class="{ 'break-color': isBreak }">
             {{ timerMinutes.toString().padStart(2, "0") }}:{{ timerSeconds.toString().padStart(2, "0") }}
           </div>
         </el-progress>
-        <p class="timer-tip">番茄钟默认 25 分钟，休息计时 5 分钟</p>
+        <p class="timer-tip">{{ isBreak ? '休息倒计时' : '番茄钟默认 25 分钟，休息计时 5 分钟' }}</p>
       </article>
 
       <article class="surface-card info-card">
@@ -430,15 +498,20 @@ onUnmounted(() => {
           </div>
           <div class="metric">
             <span>会话状态</span>
-            <strong>{{ statusText }}</strong>
+            <strong>{{ isBreak ? '休息中' : statusText }}</strong>
           </div>
         </div>
 
         <div class="action-row">
-          <el-button type="success" @click="startTimer" :disabled="timerRunning">开始</el-button>
+          <template v-if="isBreak">
-          <el-button @click="stopTimer" :disabled="!timerRunning" v-if="!timerIsOver">暂停</el-button>
+            <el-tag type="warning" effect="plain" size="large">休息中 · {{ timerMinutes }}:{{ timerSeconds.toString().padStart(2, "0") }}</el-tag>
-          <el-button @click="openFragmentDialog" :disabled="!timerRunning">生成残片</el-button>
+          </template>
-          <el-button v-if="timerIsOver" plain type="success" @click="restTimer">休息</el-button>
+          <template v-else>
+            <el-button type="success" @click="startTimer" :disabled="timerRunning">开始</el-button>
+            <el-button @click="stopTimer" :disabled="!timerRunning" v-if="!timerIsOver">暂停</el-button>
+            <el-button @click="openFragmentDialog" :disabled="!timerRunning">生成残片</el-button>
+            <el-button v-if="timerIsOver" plain type="success" @click="restTimer">休息</el-button>
+          </template>
           <el-button type="danger" plain @click="openSummaryDialog">结束会话</el-button>
         </div>
       </article>
@@ -611,6 +684,10 @@ onUnmounted(() => {
   font-weight: 700;
 }
 
+.timer-number.break-color {
+  color: #d48806;
+}
+
 .timer-tip {
   margin: 14px 0 0;
   color: var(--text-secondary);