feat(moderation): 帖评删除占位感知与硬删清场

管理删帖须填类型与理由并展示专用页；评论软删占位、版主可硬删不占楼。

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

backend/service/post.go

@@ -12,8 +12,10 @@ import (
 
 // 帖子操作错误
 var (
-	ErrPostNotFound  = errors.New("帖子不存在")
-	ErrPostForbidden = errors.New("无权限操作此帖子")
+	ErrPostNotFound     = errors.New("帖子不存在")
+	ErrPostForbidden    = errors.New("无权限操作此帖子")
+	ErrPostDeleteMeta   = errors.New("管理删除须填写类型与理由")
+	ErrPostInvalidType  = errors.New("无效的删除类型")
 )
 
 // PostService 帖子服务
@@ -384,6 +386,13 @@ type PostDetail struct {
 	Poll          *PollState          `json:"poll,omitempty"`
 	Bounty        *BountyState        `json:"bounty,omitempty"`
 	Lottery       *LotteryState       `json:"lottery,omitempty"`
+	// 软删 tombstone：列表不可见，详情专用页可读
+	Tombstone    bool       `json:"tombstone,omitempty"`
+	DeleteType   string     `json:"delete_type,omitempty"`
+	DeleteReason string     `json:"delete_reason,omitempty"`
+	DeletedBy    uint       `json:"deleted_by,omitempty"`
+	StaffDeleted bool       `json:"staff_deleted,omitempty"`
+	DeletedAt    *time.Time `json:"deleted_at,omitempty"`
 }
 
 // CreatePostInput 发帖入参
@@ -412,11 +421,23 @@ type UpdatePostInput struct {
 	AttachmentIDs *[]uint // nil=不改附件；非 nil=替换列表
 }
 
-// GetByIDForViewer 获取帖子详情（带状态可见性 + 正文访问控制）
+// GetByIDForViewer 获取帖子详情（带状态可见性 + 正文访问控制）。
+// 已软删帖返回 tombstone（无正文/附件）；已硬删或不存在返回 ErrPostNotFound。
 func (s *PostService) GetByIDForViewer(id, viewerID uint, loadActor func() *Actor) (*PostDetail, error) {
 	var post model.Post
-	if err := s.db.Preload("Board").Preload("User").First(&post, id).Error; err != nil {
-		return nil, ErrPostNotFound
+	err := s.db.Preload("Board").Preload("User").First(&post, id).Error
+	if err != nil {
+		if !errors.Is(err, gorm.ErrRecordNotFound) {
+			return nil, ErrPostNotFound
+		}
+		// 默认 scope 找不到：尝试软删行 → tombstone
+		if err := s.db.Unscoped().Preload("Board").Preload("User").First(&post, id).Error; err != nil {
+			return nil, ErrPostNotFound
+		}
+		if !post.DeletedAt.Valid {
+			return nil, ErrPostNotFound
+		}
+		return buildPostTombstone(&post), nil
 	}
 	if !visibleToPost(&post, viewerID, loadActor) {
 		return nil, ErrPostNotFound
@@ -448,6 +469,34 @@ func (s *PostService) GetByIDForViewer(id, viewerID uint, loadActor func() *Acto
 	return detail, nil
 }
 
+func buildPostTombstone(post *model.Post) *PostDetail {
+	var deletedAt *time.Time
+	if post.DeletedAt.Valid {
+		t := post.DeletedAt.Time
+		deletedAt = &t
+	}
+	staffDeleted := post.DeletedBy != 0 && post.DeletedBy != post.UserID
+	return &PostDetail{
+		ID:           post.ID,
+		BoardID:      post.BoardID,
+		UserID:       post.UserID,
+		Title:        post.Title,
+		PostType:     model.NormalizePostType(post.PostType),
+		Status:       post.Status,
+		CreatedAt:    post.CreatedAt,
+		UpdatedAt:    post.UpdatedAt,
+		Board:        post.Board,
+		User:         post.User,
+		Attachments:  []PostAttachmentDTO{},
+		Tombstone:    true,
+		DeleteType:   post.DeleteType,
+		DeleteReason: post.DeleteReason,
+		DeletedBy:    post.DeletedBy,
+		StaffDeleted: staffDeleted,
+		DeletedAt:    deletedAt,
+	}
+}
+
 func buildPostDetail(post *model.Post) *PostDetail {
 	return &PostDetail{
 		ID: post.ID, BoardID: post.BoardID, UserID: post.UserID,
@@ -954,17 +1003,53 @@ func (s *PostService) checkNewUserCooldown(userID uint) error {
 	return nil
 }
 
-// Delete 删除帖子（作者本人，或对该板块有审核权的管理成员）
-func (s *PostService) Delete(actor *Actor, postID, userID uint) error {
+// DeletePostOpts 删帖选项：staff 软删必填类型与理由；作者自删传零值
+type DeletePostOpts struct {
+	DeleteType   string
+	DeleteReason string
+}
+
+// Delete 删除帖子（作者本人，或对该板块有审核权的管理成员）。
+// staff 删除他人帖必须提供合法类型与非空理由；作者自删不写类型/理由。
+// 返回 staffDeleted 与作者 ID，供 handler 发通知。
+func (s *PostService) Delete(actor *Actor, postID, userID uint, opts DeletePostOpts) (staffDeleted bool, authorID uint, err error) {
 	var post model.Post
 	if err := s.db.First(&post, postID).Error; err != nil {
-		return ErrPostNotFound
+		return false, 0, ErrPostNotFound
 	}
-	if post.UserID != userID && !actor.CanModerateBoard(post.BoardID) {
-		return ErrPostForbidden
+	authorID = post.UserID
+
+	deleteType := ""
+	deleteReason := ""
+	if post.UserID == userID {
+		staffDeleted = false
+	} else if actor != nil && actor.CanModerateBoard(post.BoardID) {
+		deleteType = strings.TrimSpace(opts.DeleteType)
+		deleteReason = strings.TrimSpace(opts.DeleteReason)
+		if !model.ValidPostDeleteType(deleteType) {
+			return false, authorID, ErrPostInvalidType
+		}
+		if deleteReason == "" {
+			return false, authorID, ErrPostDeleteMeta
+		}
+		if len([]rune(deleteReason)) > 200 {
+			return false, authorID, errors.New("删除理由不能超过 200 字")
+		}
+		staffDeleted = true
+	} else {
+		return false, authorID, ErrPostForbidden
+	}
+
+	updates := map[string]interface{}{
+		"delete_type":   deleteType,
+		"delete_reason": deleteReason,
+		"deleted_by":    userID,
+	}
+	if err := s.db.Model(&post).Updates(updates).Error; err != nil {
+		return false, authorID, err
 	}
 	if err := s.db.Delete(&post).Error; err != nil {
-		return err
+		return false, authorID, err
 	}
-	return nil
+	return staffDeleted, authorID, nil
 }