Exactly.
>For these problems, undo and presence indicators go a long way to avoid these problems through human/social mechanisms.
x1,000 to this. This guy builds. That's exactly my takeaway as well from years working on this; provide a solid (by that I mean clearly defined) deterministic algo, and solve the rest w/ UX.
That said this sort of reconciliation can be extremely painful if people are working separately offline for any length of time as arbitrarily resolving many conflicts doesn’t necessarily result in coherent results. But as I understand it that’s also an issue for other ways of solving the issue as well.
Another missing piece is signalling failure. For example two people trying to fill the last slot of a limited resource. Having to infer from the state that comes back whether your operation succeeded or not is not a fun way to write multiplayer code.
For the former you want (as mentioned) good presence info and undo. For the latter you (sometimes) want explicitly flagged conflicts and manual resolution, like we have in git etc.
With the Replicache/Reflect model, you could actually handle both approaches. Might not be easy but the model can support it.