When resuming an old session the agent used in that old session is not selected

Describe the bug

I was in a session where I started with a specific agent (i.e. /agent x). I then resumed that session the next day and I had to select the agent again manually.

This is kind of hard to see if you don't pay close enough attention to it.

I'm also a bit unsure how big the impact is since the agent would already be in the history.

Affected version

1.0.80

Steps to reproduce the behavior

1. create a session
2. select agent /agent x (agent name should show up in the bottom bar)
3. use the session
4. /clear
5. /resume the old session
6. agent name is not shown in the bottom bar

Expected behavior

Agent that was using in the the resumed session should again be selected automatically.

Additional context

No response

首先按照描述，在 Copilot CLI 中使用 /agent、/clear 和 /resume 重现该问题。跟踪恢复的会话如何恢复其状态，以及所选 agent 如何显示在底部栏中。完成标准是：恢复会话时，会自动选择并显示会话保存时处于活动状态的 agent。