[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 |

Start by reproducing the issue in the GitHub Copilot App on Windows using the /chat path, a Word canvas, and open_canvas with focus enabled. Trace how the reported panel="open" and active="true" state relates to the side-panel rendering. Done means the canvas is visibly rendered while its metadata remains open and active.

索引モデルが issue の本文から書いたものです。