If you are entertaining ideas for the destroyed under construction problem.. I would probably just make under construction turrets not valid targets (or low-priority targets). Instead, I would pose that construction be automatically paused if not supported by an engineer while the planet is under attack (say, n amount of uncloaked units on the planet, or 1 or more largeships present. Actually just some sort of.. firepower? present,maybe an early wave's worth).
Dunno how magical Aiwar nanites are, but from an actual construction perspective it kinda makes sense. Id probably say that sort of construction logic could apply to literally anything, but hey, we probably dont need to solve problems that dont exist.