Forked session doesn't appear in Sessions in editor window

Does this issue occur when all extensions are disabled?: Yes/No

- VS Code Version: latest Insiders
- OS Version:

Steps to Reproduce:

1. Fork an existing session in the Agents window
2. Open the workspace in the editor window
3. The forked session is not listed in the sessions list

Start by reproducing the issue in the Agents window: fork an existing session, open the workspace in the editor window, and inspect the sessions list. The fix is complete when the forked session appears in the editor window's sessions list; verify the behavior with the latest Insiders build.

Written by the indexing model from the issue text.