Where is the code for engineer stations' AI code stored? Can you limit or control what it prioritizes in terms of assisting (factories vs buildings vs upgrades etc)?
Control what engi stations automatically assist?
The default behavior is determined by the Engine. You can try and manipulate it through Lua however. For example when
OnStartRepair of the Unit class is usually called when a unit starts repairing (assisting) a factory, you can then add Lua code there to adjust the behavior.
A work of art is never finished, merely abandoned