"Efficient" in the economical sense, that is. Unless, the civilization covers a very wide area (basically everywhere in there, for light years around the impend

"Efficient" in the economical sense, that is. Unless, the civilization covers a very wide area (basically everywhere in there, for light years around the impending supernova) and the protection amounted for each and every civilization zone would surpass the containment circle/cylinder/sphere around the star. In such case the sensible solution becomes to just recognize the area that can not be saved (no mater what) due to its proximity to the star and the limits of walling withstanding capacity, evacuate that, and set the containment all around the future explosion as close as possible instead.