Leaving Canvas Panel Open, Close App (runs in BG), App won't Reopen

### Short summary

Leaving a canvas extension panel open, then closing the app; but leaving it running in the background, results in the app unable to reopen. Quitting the app or ending the background task is the only way to reopen.

### Affected version or release

v1.1.10

### Installation context

Installed from github.com at https://github.com/features/ai/github-app

### What happened?

Using several downloaded and installed, along with several locally installed canvas extension I found that:

- In settings, if "Keep open when window is closed" is toggled on and a canvas extension panel is open on close, then the app will not reopen
- Quitting the app is the only way to reopen it
- When the canvas panel is closed, and in the same conversation (*or any window without a running canvas extension panel open*) then close the app again, then it is able to reopen

### Steps to reproduce

1. Ensure that "Keep open when window is closed" is toggled on
2. Start a conversation, and start a canvas extension
3. Leave the canvas extension panel open
4. Close the app
5. App will not reopen
- Tried on 2 Windows 11 OS

### Expected behavior

The app to open.

### Additional context

_No response_

Windows 11 で "Keep open when window is closed" を有効にし、会話をアクティブにした状態で、アプリを終了する前に canvas 拡張パネルを開いたままにして再現します。まず、アプリのバックグラウンドライフサイクルと canvas パネルのシャットダウン動作を追跡します。アプリが終了したりバックグラウンドタスクを終了したりせず、正常に再度開くようになれば完了です。

索引モデルが issue の本文から書いたものです。