[Bugs] Title: Canvas side panel not visible despite being reported as open and active

**Mood:** 😊
**Category:** Bugs

Title: Canvas side panel not visible despite being reported as open and active

Steps to Reproduce:

Open a project session in the Github Copilot App (v1.0.64-0, Windows)
Agent opens a Word canvas via open_canvas with placement: { focus: true }
System reports canvas as panel="open" and active="true"
Side panel is not visible — user cannot see it
Workarounds tried: Re-opening with focus, opening second instance, rebooting — none worked.

Expected: Panel renders visibly. Actual: Panel metadata says open/active but nothing appears on screen.

Env: v1.0.64-0, Windows, Word canvas (docx), workspace scope. #MAI

---
| Field | Value |
| --- | --- |
| App version | 1.0.3 |
| OS | Windows 10.0.26200 |
| Theme | GitHub |
| Path | /chat |
| Tenure | Week 2 |

首先，在 Windows 上的 GitHub Copilot App 中使用 /chat 路径、Word canvas 以及启用焦点的 open_canvas 重现该问题。跟踪报告的 panel="open" 和 active="true" 状态与侧边面板渲染之间的关系。完成的标准是 canvas 可见地渲染出来，同时其元数据仍保持打开和活动状态。

由索引模型根据 Issue 内容生成。