Process closed error dialog spam

[cromachina]

Describe the bug
If a program is closed when looking at the process list, and then that stale process is selected, there is a threading error dialog about the process no longer existing that is constantly spammed. I have to go to another TTY to hard kill the program because the popup window can steal focus from the whole system.

To Reproduce
Steps to reproduce the behavior:

1. Open the App
2. Attach to any process
3. Open a new process, like a terminal instance
4. Open the process selector
5. Close the process that was opened in step 3
6. Attempt to attach to the previously closed process

Expected behavior
A single error should be reported that the process cannot be attached to since it no longer exists.

System (please complete the following information):

• OS: NixOS (Linux)
• Python Version 3.14