Manual `/rename` is overwritten by later auto-generated session name

### Describe the bug

A session name set manually via `/rename ` does not persist reliably. After continuing to work in the same session, Copilot CLI auto-renames the session again and overwrites the user-defined name.

### Affected version

GitHub Copilot CLI 1.0.22

### Steps to reproduce the behavior

1. Start a new Copilot CLI session.
2. Run `/rename my-name`.
3. Continue working in the same session for a while.
4. Check the session name again, or try to find it later in `/resume`.

### Expected behavior

A manually assigned session name should remain unchanged until the user explicitly renames it again.

### Additional context

- Actual behavior: the manual name is replaced by an automatically generated session name.
- Impact: renamed sessions become hard to find later because the expected custom name no longer exists.
- OS: Windows
- Terminal: Windows Terminal
- Shell: PowerShell

まず `/rename` と `/resume` を使って問題を再現し、その後、手動で設定された名前と、後から自動生成されるセッション名がどこで処理されているかを追跡します。`/rename` で設定した名前が作業を続けても変わらず、明示的に再度名前を変更するまで、その名前で `/resume` に表示され続ければ作業は完了です。

索引モデルが issue の本文から書いたものです。