> A user’s very first sync is likely to be the largest one, to seed all the data into the could.

You are almost guaranteed that the first sync results in zero conflicts. It's just a mass-upload. Even if you bring other clients in, there is still a very low chance and "last-one-wins" is a pretty decent policy for who gets the original filename and then other gets a " (copy)" suffix or something. Doesn't really matter as long as it's documented and intuitive.

FWIW having built a sync service I can tell you that this is an issue in practice, and you have to test for these differences in any event.

My point is that for a weekend PoC that you want to use for yourself… it’s rather a non-issue. Further, you need to create a lot of primitives before you can even tackle the problem correctly, so initially, it is an unsolvable problem until you have those primitives.