So far we've gotten a lot of answers and the only questions I have is what was the purpose of the Nightwalker and did the Praeses arrive at the end of the great war and everyone was too busy killing each other to notice?
My theory about the Nightwalker is it might have been left behind as a guardian to prevent this kind of discontinuity infection, but after enough pairs of habitat dwellers were attacked and stripped of their nanotech the Nightwalkers burned out completely.
Well, base on Alice talking about the Praeses wanting to 'reclaim' earth, they were clearly already on earth well before the war ended and presumably before it even started. That'd also explain how Alice/Sedna know so much about the Praeses.
I have many more questions, including:
1) The Blink seems to have moved the Praeses from earth to orbit, and Alice thinks they want to come back to earth. What has prevented the Praeses from coming to earth all this time?
2) Was the Blink indeed caused by the AI, and was it meant to get rid of the Praeses from earth?
3) What was the function of the nightwalker? My theory is also that it was left behind as some sort of emergency system (i.e. get rid of nanotech from earth). But were they left by the AI in case the Praeses indeed wanted to come back to reclaim earth, or somebody else? My thoughts are that they were left by the AI to remove Praeses-based nanotech, since they got rid of Gavia's tech and left Ardent with his pico-tech alone.
4) Are the Praeses benevolent/harmless aliens, as they seem to claim, or are they evil, do they want to take over/control earth? Did they simply 'simulate' realities, or did they upload the consciousnesses of actual humans in their networks, removing them from earth?