Plan tab empty after changing to Changes and back to Plan

### Short summary

The plan tab only rendered a white page after being previously filled. I just switched tabs to "changes" and back to "plan"

### Affected version or release

v.0.2.8

### Installation context

_No response_

### What happened?

I had a weird one time bug today, which I can't reproduce, (un-)fortunately. But still, I want to report it.

The GitHub Copilot App was in plan mode and created a plan for my. I noticed the tabs "Changes", "Plan" and "Terminal". The tab control was opened with the Plan tab selected and with a filled plan.
After clicking on the "Changes" tab and going back to the Plan tab, the plan disappeared

and I couldn't get it back. Clicking on "view full plan" again also did not refresh the rendering. Only after writing in the chat prompt and updating the plan, I was able to get it back.

I assume that the plan was cached locally but somehow the plan got evicted from the cache?

### Steps to reproduce

_No response_

### Expected behavior

_No response_

### Additional context

_No response_

首先在 plan mode 下运行 GitHub Copilot App，并从 Plan 标签切换到 Changes 后再切回来。该 issue 没有指定文件、测试或入口点，并且报告的问题无法复现。当现有计划在切换标签后仍然可见，且该行为由可复现的检查覆盖时，即表示完成。

由索引模型根据 Issue 内容生成。