Agent-created worktree sessions default to Local and disappear

### Type of issue

Bug

### Description

When asking Copilot in a normal VS Code window to create worktrees and do work in them, the newly created sessions are assigned to **Local** rather than the current workspace when using voice mode. They do not appear to retain awareness of the workspace, and after creation the session can disappear from the expected session list.

### Steps to reproduce

1. Open a workspace in the normal VS Code window.
2. Ask Copilot to create one or more worktrees and perform work in them using voice mode
3. Observe the newly created agent sessions.

### Expected behavior

The sessions remain associated with the originating workspace/worktrees and remain visible in the expected session list.

### Actual behavior

The sessions are created under **Local**, appear not to know about the originating workspace, and can vanish after creation. Instead, the sessions should use whatever harness is selected or default to **Copilot**.

Reported by @jamesmontemagno in Slack with a screen recording.