Before I start writing sync code for Scorebook, I figured I should learn about how CloudKit works. Here are some resources that I'm using.
And also for sync systems, I'm thinking through the best way to handle keys and trigger events within the app. Brent Simmons wrote an (in)essential diary as he was adding sync to Vesper.
I'm going to look for some more resources as I go along, and anything that is of use I'll be sure to link to. I've been going through the process of how it should work over and over in my head. I'm looking forward to putting it out and seeing if my thinking is correct. Hopefully the result of this all will be the best possible product I can ship.