feat: add practice session resume

apps/taro/src/pages/student/practice/index.tsx

@@ -4,6 +4,7 @@ import { Button, Text, Textarea, View } from '@tarojs/components';
 import { loadCollectionQuestions, loadQuestions } from '@/services/catalog';
 import {
   createPracticeSession,
+  loadPracticeSessionDetail,
   submitAnswer,
   submitPracticeSession,
   toggleQuestionFavorite,
@@ -66,6 +67,27 @@ function answerLabel(state?: AnswerState) {
   return state.selfJudged ? '已自评' : '已答';
 }
 
+function answersFromBackend(answers?: Record<string, AnswerResult>): Record<string, AnswerState> {
+  const result: Record<string, AnswerState> = {};
+  for (const [questionId, answer] of Object.entries(answers || {})) {
+    result[questionId] = {
+      selectedOptions: Array.isArray(answer.selectedOptions) ? answer.selectedOptions : [],
+      answerText: answer.answerText || '',
+      isCorrect: answer.isCorrect,
+      answeredAt: answer.answeredAt,
+      selfJudged: answer.selfJudged,
+    };
+  }
+  return result;
+}
+
+function secondsUntil(value?: string | null) {
+  if (!value) return null;
+  const parsed = new Date(value).getTime();
+  if (!Number.isFinite(parsed)) return null;
+  return Math.max(0, Math.ceil((parsed - Date.now()) / 1000));
+}
+
 export default function StudentPracticePage() {
   const router = useRouter();
   const params = router.params || {};
@@ -85,6 +107,7 @@ export default function StudentPracticePage() {
   const [error, setError] = useState('');
 
   useEffect(() => {
+    const practiceSessionId = params.practiceSessionId || undefined;
     const collectionId = params.collectionId || undefined;
     const body = {
       blueprintId: params.blueprintId || undefined,
@@ -94,6 +117,27 @@ export default function StudentPracticePage() {
       mode: params.mode || 'sequential',
       questionLimit: 50,
     };
+
+    if (practiceSessionId) {
+      loadPracticeSessionDetail(practiceSessionId)
+        .then(payload => {
+          const nextSession = payload.item;
+          const backendAnswers = answersFromBackend(nextSession.answersByQuestion);
+          setSession(nextSession);
+          setQuestions(nextSession.questions || []);
+          setAnswerByQuestion(backendAnswers);
+          const savedIndex = getStorage<number>(indexStorageKey(nextSession.id));
+          const firstUnanswered = (nextSession.questionIds || []).findIndex(questionId => !backendAnswers[questionId]);
+          setIndex(typeof savedIndex === 'number' ? savedIndex : Math.max(0, firstUnanswered));
+          const remaining = secondsUntil(nextSession.expiresAt);
+          if (remaining !== null) setTimeLeft(remaining);
+          if (nextSession.status === 'finished') setCompleted(true);
+        })
+        .catch(nextError => setError(nextError instanceof Error ? nextError.message : '练习恢复失败'))
+        .finally(() => setLoading(false));
+      return;
+    }
+
     createPracticeSession(body)
       .then(async payload => {
         const nextSession = payload.item;