Copilot CLI screen goes blank when using /new to start a new session

### Describe the bug

Copilot CLI screen goes blank when using /new to start a new session with an already running session currently being worked on

### Affected version

1.0.67

### Steps to reproduce the behavior

1. This happens intermittently but often enough to get bothersome
2. Usual scenario that I've noticed, I have a long running session which is running, and I want to start a new session with /new
3. The /new makes the CLI screen blank with no escape back to the previous session
4. The only way I've been able to get out of this situation is to kill the process and start CLI over again

### Expected behavior

Ability to create a new session and work across sessions while the previous session continues in the background

### Additional context

_No response_

未指定文件或测试。先在另一个会话正在运行时，使用 CLI /new 命令复现间歇性空白屏幕，然后跟踪会话切换入口。完成标准是：/new 能创建一个可用的新会话，同时之前的会话继续在后台运行，而无需终止进程。

由索引模型根据 Issue 内容生成。