[Bug] Preview pane freezes during inline text editing in Artifact canvas on Chrome/Mac

**Bug Description**
design キャンバス（Artifact）で文字のインライン編集中にプレビュー枠だけ止まる。Chrome/Mac。エディタ本体は動き Save
は押せる。再現は不安定で同じ操作でも止まらない回がある。こまめに Save で回避中

**Environment Info**
- Platform: darwin
- Terminal: Apple_Terminal
- Version: 2.1.263
- Feedback ID: cede6856-43d3-4977-83d8-4298ab373dd8

**Errors**
```json
[]
```

Start from the Artifact design canvas and inline text editing flow mentioned in the report, reproducing on Chrome/Mac with version 2.1.263 if possible. Use the Feedback ID and the empty Errors block as context. Done means the preview pane no longer freezes during inline text editing while the editor and Save remain usable.

由索引模型根据 Issue 内容生成。