With regard to: > in principle you could create a “mirror human” with everything flipped, which is good because it’s insane and they would be immune to infecti

With regard to: > in principle you could create a “mirror human” with everything flipped, which is good because it’s insane and they would be immune to infectious disease but also to food so to keep them alive you’d need an entire mirror life ecosystem, although where is my mirror life science fiction I highly recommend Neal Stephenson's _Anathem_.