[Bug]: Plan proposed changes lost when viewing a file

### Platform

macOS

### Operating system version

macOS Tahoe 26.3.1 (a)

### System architecture

ARM64 (M1, M2, etc)

### PolyScope Version

0.12.1

### Bug description

While proposing changes to a plan, I opened a file to reference something. When I closed the file, the proposal text box was gone.

### Steps to reproduce

- Make a plan
- Click "Propose changes"
- Start typing something
- cmd+k, go to file, pick a file
- Close file
- Your changes are gone and you're back at the "Approve"/"Autopilot"/"Propose changes" buttons

### Relevant log output

```shell

```