fix(chat): 修复一键清理未读失败

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
+	})
+}