fix: 修复多选题提交后页面崩溃

- formatCorrectAnswer: 增加空值保护和 try-catch
- checkObjectiveAnswer: 增加 options 数组校验
- recordWrongAnswer: 使用 dialogQuestion 快照，增加错误处理

frontend/src/views/exam/practice.vue

@@ -772,23 +772,35 @@ const submitAnswer = () => {
 const checkObjectiveAnswer = (): boolean => {
   const q = currentQuestion.value
   
+  if (!q) {
+    console.error('checkObjectiveAnswer: currentQuestion 为空')
+    return false
+  }
+  
+  try {
     if (q.type === 'single' || q.type === 'multiple') {
+      // 增加空值保护
+      if (!q.options || !Array.isArray(q.options)) {
+        console.error('checkObjectiveAnswer: options 无效', q.options)
+        return false
+      }
+      
       const correctIndexes = q.options
-      .map((opt: any, idx: number) => opt.isCorrect ? idx : -1)
+        .map((opt: any, idx: number) => opt?.isCorrect ? idx : -1)
         .filter((idx: number) => idx !== -1)
       
       // 调试日志：显示正确答案索引和用户选择
-    console.log(`🔍 客观题判断 - 题目: "${q.title.substring(0, 30)}..."`)
+      console.log(`🔍 客观题判断 - 题目: "${q.title?.substring(0, 30) || '无标题'}..."`)
       console.log(`   选项详情:`, q.options.map((opt: any, idx: number) => ({
         index: idx,
         letter: String.fromCharCode(65 + idx),
-      isCorrect: opt.isCorrect,
-      content: opt.content?.substring(0, 20) + '...'
+        isCorrect: opt?.isCorrect,
+        content: opt?.content?.substring(0, 20) + '...'
       })))
       console.log(`   正确答案索引: [${correctIndexes.join(', ')}]`)
       console.log(`   用户选择索引: [${userAnswer.selected.join(', ')}]`)
       
-    const isCorrect = JSON.stringify(userAnswer.selected.sort()) === JSON.stringify(correctIndexes.sort())
+      const isCorrect = JSON.stringify([...userAnswer.selected].sort()) === JSON.stringify([...correctIndexes].sort())
       console.log(`   判断结果: ${isCorrect ? '✅正确' : '❌错误'}`)
       
       return isCorrect
@@ -798,6 +810,10 @@ const checkObjectiveAnswer = (): boolean => {
     }
     
     return false
+  } catch (error) {
+    console.error('checkObjectiveAnswer 出错:', error)
+    return false
+  }
 }
 
 /**
@@ -863,18 +879,29 @@ const checkSubjectiveAnswer = async (question: any): Promise<boolean> => {
  * 记录错题到数据库
  */
 const recordWrongAnswer = async () => {
-  const q = currentQuestion.value
+  // 使用 dialogQuestion（已保存的题目快照）而不是 currentQuestion
+  const q = dialogQuestion.value || currentQuestion.value
+  
+  if (!q) {
+    console.error('recordWrongAnswer: 题目数据为空')
+    return
+  }
   
   // 获取用户答案
   let userAnswerText = ''
+  try {
     if (q.type === 'single' || q.type === 'multiple') {
       userAnswerText = userAnswer.selected.map(idx => String.fromCharCode(65 + idx)).join(',')
     } else if (q.type === 'judge') {
       userAnswerText = userAnswer.judge ? '正确' : '错误'
     } else if (q.type === 'blank') {
-    userAnswerText = userAnswer.blank
+      userAnswerText = userAnswer.blank || ''
     } else if (q.type === 'essay') {
-    userAnswerText = userAnswer.essay
+      userAnswerText = userAnswer.essay || ''
+    }
+  } catch (e) {
+    console.error('获取用户答案失败:', e)
+    userAnswerText = ''
   }
   
   try {
@@ -883,10 +910,10 @@ const recordWrongAnswer = async () => {
       round: currentRound.value,  // 记录当前轮次
       question_id: null,  // AI生成的题目没有question_id
       knowledge_point_id: q.knowledge_point_id || null,
-      question_content: q.title,
+      question_content: q.title || '',
       correct_answer: formatCorrectAnswer(q),
       user_answer: userAnswerText,
-      question_type: q.type  // 新增：记录题型
+      question_type: q.type || ''  // 新增：记录题型
     })
   } catch (error: any) {
     console.error('记录错题失败:', error)
@@ -1181,22 +1208,28 @@ const renderMarkdown = (content: string): string => {
  * 格式化正确答案
  */
 const formatCorrectAnswer = (question: any) => {
+  if (!question) return ''
+  
+  try {
     if (question.type === 'single' || question.type === 'multiple') {
       // 如果有correctAnswer字段（来自Dify的原始correct）
       if (question.correctAnswer) {
         // 多选题格式优化：将 "A：xxx、B：xxx" 或 "A：xxx,B：xxx" 改为换行显示
         // 使用更精确的匹配：提取完整的选项格式 X：内容
         const optionPattern = /([A-Za-z][：:])([^A-Za-z]*?)(?=(?:[,、]?[A-Za-z][：:])|$)/g
-      const matches = [...question.correctAnswer.matchAll(optionPattern)]
+        const matches = [...String(question.correctAnswer).matchAll(optionPattern)]
         if (matches.length > 1) {
           // 多个选项，换行显示
           return matches.map(m => m[1] + m[2].trim()).join('\n')
         }
         return question.correctAnswer
       }
-    // 否则从options中提取
+      // 否则从options中提取（增加空值保护）
+      if (!question.options || !Array.isArray(question.options)) {
+        return ''
+      }
       return question.options
-      .map((opt: any, idx: number) => opt.isCorrect ? String.fromCharCode(65 + idx) : null)
+        .map((opt: any, idx: number) => opt?.isCorrect ? String.fromCharCode(65 + idx) : null)
         .filter((v: any) => v)
         .join('、')
     } else if (question.type === 'judge') {
@@ -1210,6 +1243,10 @@ const formatCorrectAnswer = (question: any) => {
       return question.correctAnswer || ''
     }
     return ''
+  } catch (error) {
+    console.error('formatCorrectAnswer 出错:', error, question)
+    return question.correctAnswer || ''
+  }
 }
 
 /**