Add a method to /exit from Copilot CLI regardless of nested sessions

Describe the feature or problem you'd like to solve

Add a method to /exit from Copilot CLI regardless of nested sessions

Proposed solution

Add a /exit behavior that gracefully terminates the current Copilot CLI, either by changing the /exit behavior, adding a subcommand or adding a separate command.

Example prompts or workflows

N/A

Additional context

When using a Copilot CLI session, and running several /new sessions after completing unrelated work, invoking the /exit command will currently exit the current session and show the previous one - instead of existing Copilot CLI.

This matches behavior matches with the current docs:

/exit, /quit: Close the current session. If other sessions are running, this foregrounds the newest remaining one instead of quitting. Quits the CLI only when it is the last open session. /exit print always tears down the CLI and offers to dump the transcript.

To fully close Copilot CLI after multiple /new turns on either has to run /exit multiple times or terminate the process.

まず、既存の /exit コマンドと、複数の /new セッションの後に使用されるセッション処理を追跡します。ネストされたセッションで文書化された動作を再現し、そのうえで、選択した /exit の動作によって Copilot CLI 全体が終了し、適切な場合には既存の現在のセッションの動作が維持されることを確認します。