External sessions are slow appear, filter, and in some cases don't filter at all

Testing #331122

A session created in copilot or the GH app takes at least two minutes to appear for the first time, seemingly not showing up until after I reload window.

Setting filter to `None` in the session list takes a minute or two to exclude external sessions like the `.copilot` folder, but for some reason sessions from standard folders won't be filtered out.

The scenario in the video highlights how selecting `None` filter will exclude the `.copilot` folder after a little while, but the "Quote homer simpson" session stays in the list, even though it was created by copilot in the vscode folder

https://github.com/user-attachments/assets/0ef4add0-0704-4ff9-b904-53f57876acc6