And I wonder how you do it. How are you able to suspend and resume work on a complex project like this? How are you able to stop thinking about it when scheduled time is up, and then pick it up the next day, without paying a huge time cost of loading yesterday's state back into your head?

Could you elaborate on this? I'm asking seriously - I myself wish I could do that. The way I work today, in irregular but long bursts of high focus, is somewhat effective, but doesn't lend itself to having a balance in life (work-life balance, but also "personal interests - life balance").