At the moment, saving proceeds as follows: 1. collect data; 2. build big object; 3. serialize object; 4. send to worker for writing. I would like to replace step 2 by something a little more abstract that will later let us rework the back-end without having to rewrite everything.

Comment on attachment 8361116 [details] Rough sketch of a possible API Yes, that seems like an interesting thing to have and it would probably make the code a little more explicit about what just happened and why we're updating state. It seems like a big project though so I wouldn't really want to tackle that until we're sure we're doing something that would profit from differential updates.

Turning this into a meta-bug, as we'll be doing this piece-wise.

Note that the ongoing work is about providing access to the state (i.e. replacing `getBrowserState` & co.), not changing state in a way that will be mirrored automatically by the DOM (i.e. we are not replacing `setBrowserState` & co.).