On your terraforming mirror/ shade idea.
good idea, I really like it! However I'd not have it time intensive, but rather maintenance intensive.
Since they are not providing a permanent alteration to the environment, but directly increasing/decreasing the albedo *
(* actually altering received solar radiation, but albedo is the factor that comes closest from those listed in the environmental box of the sysgenscreen).
It is the quick fix approach to planetary engineering:
They would be fairly cheap to build (similar cost to infrastructure, but utilising another TN element), and you would still require quite a number for them to be effective, but their effect on planetary base temperature (or albedo, whichever works) would be instantaneous.
The drawback is that they would also require maintenance. Or alternatively take up pop like infra does.
The best option would be to have them decay (orbital).
(one unit could in/decrease basetemp by one degree one year one, but this decays by 0.1 each year. or 10%/year for the entire unit to fail).
They would be equally succeptable to collateral damage as infrastructures, but not directly targetable like shipyards.
my two creds.
