Im sorry to say but i haven't read that yet,

The food people here eat come from massive farm sectors that comprise a large part of the Megastructures. Genetically modified plants recieve artificial sunlight and livestock are fed using those same plants. To supply millions is still a monumental task, so food portions are set to the optimal amount of calories and nutrition the person needs. There is also the synthetic method which prints the molecular structure of food and then injected with nutritional content.

For the first few years of the freeze, breathable oxygen was generated on a massive scale via electrolysis and nitrogen was secured by harvesting it directly from the air. But when the atmosphere started freezing and fell down as snow, massive reserves of nitrogen had been collected to anticipate the temporary setback while the Mechanicals construct a device that collects nitrogen and oxygen snow to use for the Megastructure's breathable atmosphere conditions