fix(chat): 修复一键清理未读失败

backend/internal/modules/chat/handler_admin.go

@@ -82,6 +82,19 @@ func (h *Handler) AdminMarkRead(c *gin.Context) {
 	h.markRead(c, Principal{Type: "admin", ID: adminID})
 }
 
+func (h *Handler) AdminMarkAllRead(c *gin.Context) {
+	adminID, ok := currentAdminID(c)
+	if !ok {
+		response.Unauthorized(c, "缺少管理员上下文")
+		return
+	}
+	if err := h.service.MarkAllAdminConversationsRead(c.Request.Context(), adminID); err != nil {
+		writeChatError(c, err)
+		return
+	}
+	response.OK(c, gin.H{"read": true})
+}
+
 func (h *Handler) AdminTransfer(c *gin.Context) {
 	adminID, ok := currentAdminID(c)
 	if !ok {

backend/internal/modules/chat/message.go

@@ -239,3 +239,31 @@ func (r *Repository) MarkRead(ctx context.Context, principal Principal, conversa
 	}
 	return nil
 }
+
+// MarkAllAdminConversationsRead advances one admin's read cursor for every conversation in one transaction.
+func (r *Repository) MarkAllAdminConversationsRead(ctx context.Context, adminID uint64) error {
+	now := time.Now()
+	return r.db.WithContext(ctx).Transaction(func(tx *gorm.DB) error {
+		// 先补齐状态行，再更新游标。拆成两步可兼容本地 MySQL/MariaDB 对
+		// INSERT ... SELECT 同表读取并 ON DUPLICATE KEY UPDATE 的限制。
+		if err := tx.Exec(`
+			INSERT INTO chat_admin_conversation_states
+				(conversation_id, admin_user_id, remark, last_read_message_id, last_read_at)
+			SELECT c.id, ?, COALESCE(existing.remark, ''), COALESCE(c.last_message_id, 0), ?
+			FROM chat_conversations AS c
+			LEFT JOIN chat_admin_conversation_states AS existing
+				ON existing.conversation_id = c.id AND existing.admin_user_id = ?
+			WHERE existing.id IS NULL`, adminID, now, adminID).Error; err != nil {
+			return err
+		}
+		return tx.Exec(`
+			UPDATE chat_admin_conversation_states AS cas
+			JOIN chat_conversations AS c ON c.id = cas.conversation_id
+			SET cas.last_read_message_id = c.last_message_id,
+				cas.last_read_at = ?,
+				cas.updated_at = CURRENT_TIMESTAMP
+			WHERE cas.admin_user_id = ?
+			  AND c.last_message_id IS NOT NULL
+			  AND cas.last_read_message_id < c.last_message_id`, now, adminID).Error
+	})
+}

backend/internal/modules/chat/service.go

@@ -131,6 +131,16 @@ func (s *Service) MarkRead(ctx context.Context, principal Principal, conversatio
 	return s.repo.MarkRead(ctx, principal, conversationID)
 }
 
+func (s *Service) MarkAllAdminConversationsRead(ctx context.Context, adminID uint64) error {
+	if s.repo == nil {
+		return ErrDependencyUnavailable
+	}
+	if adminID == 0 {
+		return ErrPermissionDenied
+	}
+	return s.repo.MarkAllAdminConversationsRead(ctx, adminID)
+}
+
 func (s *Service) TransferConversation(ctx context.Context, principal Principal, conversationID uint64, req TransferRequest) error {
 	if s.repo == nil {
 		return ErrDependencyUnavailable