清除业务契约双读：抽奖/草稿/时间戳/邮件只认新格式，并删除 legacy 短代码改写。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/service/post_interact.go

@@ -49,7 +49,7 @@ type LotteryPrize struct {
 
 type LotteryMeta struct {
 	Prizes     []LotteryPrize `json:"prizes"`
-	Slots      int            `json:"slots"` // 由 prizes 数量合计推导，兼容旧数据
+	Slots      int            `json:"slots"` // 由 prizes 数量合计，仅便于展示/校验
 	Drawn      bool           `json:"drawn"`
 	WinnerIDs  []uint         `json:"winner_ids"`
 	Closed     bool           `json:"closed"`
@@ -122,13 +122,7 @@ func parseLotteryMeta(raw string) (*LotteryMeta, error) {
 	if err := json.Unmarshal([]byte(raw), &m); err != nil {
 		return nil, errors.New("抽奖配置无效")
 	}
-	// 旧数据只有 slots：合成单一奖品项
-	if len(m.Prizes) == 0 && m.Slots > 0 {
-		m.Prizes = []LotteryPrize{{Name: "奖品", Count: m.Slots}}
-	}
-	if len(m.Prizes) > 0 {
-		m.Slots = lotterySlotsFromPrizes(m.Prizes)
-	}
+	m.Slots = lotterySlotsFromPrizes(m.Prizes)
 	return &m, nil
 }
 
@@ -592,16 +586,12 @@ func (s *PostService) buildQuestionState(post *model.Post, viewerID uint, canMan
 	}
 	floor := FloorNumber(s.db, post.ID, m.AcceptedCommentID)
 	answer := s.loadAcceptedAnswer(post.ID, m.AcceptedCommentID, floor, viewerID, isMod)
-	solvedAt := m.SolvedAt
-	if m.Solved && solvedAt == "" && answer != nil && !answer.CreatedAt.IsZero() {
-		solvedAt = answer.CreatedAt.UTC().Format(time.RFC3339) // 旧数据：无 solved_at 时用采纳评论时间
-	}
 	return &QuestionState{
 		Solved:            m.Solved,
 		AcceptedCommentID: m.AcceptedCommentID,
 		AcceptedFloor:     floor,
 		AcceptedAnswer:    answer,
-		SolvedAt:          solvedAt,
+		SolvedAt:          m.SolvedAt,
 		CanAccept:         canManage && !m.Solved,
 		CanSolve:          canManage && !m.Solved,
 		// 已采纳答案后不可重新打开；仅「手动标已解决」可撤回
@@ -688,17 +678,13 @@ func (s *PostService) buildPollState(post *model.Post, viewerID uint, canClose b
 		opts[i] = stat
 	}
 	voters := len(voterSet)
-	closedAt := m.ClosedAt
-	if m.Closed && closedAt == "" {
-		closedAt = m.EndsAt // 旧数据：无 closed_at 时用截止时刻兜底
-	}
 	return &PollState{
 		Options:        opts,
 		Multi:          m.Multi,
 		Closed:         m.Closed,
 		Anonymous:      m.Anonymous,
 		EndsAt:         m.EndsAt,
-		ClosedAt:       closedAt,
+		ClosedAt:       m.ClosedAt,
 		TotalVotes:     total,
 		Voters:         voters,
 		MyOptions:      my,