Can't return to parent process from sub-process

### Describe the Bug

The diff of sub-processes does not work as intended, only one pane enters the sub-process. Additionally it's not possible to come out of a sub-process.

### Steps to Reproduce

1. Diff a process that contains a collapsed sub-process element
2. Click on the arrow to enter that sub-process
3. => It's not possible to come back to the parent

### Expected Behavior

We should be able to navigate back to the parent.

Reproduce the issue by diffing a process containing a collapsed sub-process, then use the arrow to enter it. Trace the sub-process navigation entry point and compare how both panes change; done means the diff enters consistently and provides a way to return to the parent process.

Written by the indexing model from the issue text.