I would expect to navigate within the diff on the right hand side.

Me too

@bpasero Is that something that the editor service supports via some kind of option or is this something that needs alex-editor knowledge?

@jrieken we have a similar problem for the editor commands that start a navigation (e.g. "Go to definition"). If the definition is in the same file, we do not want to exit the diff editor. All of the editor commands leverage ICodeEditorService.openCodeEditor() for this purpose. This one is implemented in the workbench to support diff editors. Can you give it a try and see if that works? It should be a drop-in replacement for IEditorService#openEditor() for the basic scenarios of opening text editors. It will forward to the IEditorService.openEditor() if there is no diff editor involved.