I'd be really interested to hear more about your approach. Maybe you’d write it up?

I did consider simply storing and replaying actions, but realised I'd still want a way to merge them: consider a series of actions like: "add item", "update item", "add item", ...<lots more changes>..., "delete items 1 through 20". If there’s no merge, a lot of redundant actions will end up building up in the offline case.

There are a lot of ways to approach this (I’m reading Brent Simmon’s adventures (http://inessential.com/2014/05/24/vesper_sync_diary_follow-u...) with interest at the moment).