Large messages containing reasoning, tool lists, or long replies could use an estimated off-screen height that left later content outside the reachable scroll range. Conversation messages now participate in layout with their actual height while the existing 80-message render window keeps long histories bounded. Release note: 修复偶发的长会话滚动条提前到底问题;包含较长推理、工具记录或正文时,现在可以直接滚动查看全部已加载内容,无需切换会话刷新。