Command Block UI Overhaul

Fixed Issues

• After setValue truncation, layout still used the original long text
• A single insert/delete triggered the responder multiple times, and the cursor briefly jumped to the end of the full text in between
• Reducing the maximum length did not rebuild lines or the cursor
• Word deletion used UTF-16 length but converted to code point offsets
• Unicode text truncation could split surrogate pairs
• Mouse positioning ignored the top padding and lacked drag selection
• Multiple usage/error messages used the same Y coordinate
• The completion list had no screen boundary handling, and scrolling to the last item was offset
• Old asynchronous completion requests could refresh new input, and callbacks were not thread-confined
• After suggestions were closed, late requests could still reopen them
• Enter-to-save did not check whether Done was available; resizing directly enabled controls
• Subsequent command block packets reinitialized the edited content
• Toggling the output switch directly modified the client-side block object
• The multi-line container used LinkedList but frequently accessed by index

New Features

• Undo/redo: 100 bounded snapshots restoring text, cursor, and selection; new edits clear the redo branch.
• Mouse multi-line drag selection and edge scrolling.
• Window resizing preserves editing state and undo history.

已修复的问题

• setValue 截断后仍用原始长文本排版
• 一次插入/删除多次触发 responder，且中间光标先跳到全文末尾
• 缩短最大长度未重建行与光标
• 按 UTF-16 长度删除单词却转成 code point 偏移
• Unicode 文本截断可能拆开代理对
• 鼠标定位忽略顶部内边距，缺少拖选
• 多条 usage/error 提示使用同一个 Y 坐标
• 补全列表无屏幕边界处理，滚动到末项有偏差
• 旧异步补全请求可刷新新输入，回调线程不受限
• 关闭建议后迟到的请求仍可重新弹出
• Enter 保存不检查 Done 是否可用；缩放直接启用控件
• 后续命令方块数据包重复初始化编辑内容
• 切换输出开关直接修改客户端方块对象
• 多行容器使用 LinkedList 却频繁按索引访问

新功能

• 撤销/重做：100 次有界快照，恢复文本、光标和选区；新修改清空 redo 分支。
• 鼠标多行拖选和边缘滚动。
• 窗口缩放保留编辑状态和撤销历史。