Currently, when a new UUnrealEdEngine C++ child class is created, created file links to
#include "Editor/UnrealEdEngine.h"
However this include causes a bunch of errors while compiling, starting with base class undefined, plus a few thousand lines more.
UnrealEdEngine.h(89): error C2504: 'UEditorEngine': base class undefined
Replacing the include with this one solves the compile problem:
#include "UnrealEd.h"
The editor runs, and code works as expected.