[emacsen]

I used to think this a lot, but then I find products that do exactly this and work reliably most of the time by simply asking you "Local Version" or "Server Version". This is what Steam does, what Nextcloud does, what PS5 does, and probably others. It's a naive approach but it seems to work well enough.

Beyond that, you get into complex territory but maybe we've all been overthinking the problem space.

[JamesSwift]

It only works for certain classes of products. A game has decidedly few copies (will just be your own saves across multiple devices), and is already serializing in a singular high-level format. When you have business software that is used my multiple people, and has multiple different 'kinds' of things that are being reconciled (at varying levels of granularity), it gets really messy and really hard to hit the sweet spot.