If the correctness of my program depends on the ordering of data (for operations that would otherwise be commutative), that seems like that should be something explicit rather than implicit.

I'm not sure if I agree that "hidden setting actually keeps your data correct" is something that should be the default.

Is "non-deterministic" the right description for this? I read it as describing an implementation where ordering is not preserved, but deterministically. Is that a misreading?

This is a tricky field, the problem is not actually the non-determinism of the processing algorithms, but implicit ordering of the data.[1] The implicit ordering of the data is a footgun that -- as seen in the paper -- has already claimed victims. Using algorithms that don't need to upkeep the ordinality requirement in every operation will definitely move the library to a better direction and make future data modeling better and more explicit.

[1] Aha, now I see why language models use this so frequently and why it might be overrepresented in the data. This is a perfect way to move the blame from the person you're responding to, if they're mistaken. They probably have a super, super overtuned "politeness" gym using sentiment analysis that tries to reword answers to not blame the misunderstandings of the person. Then this blame shifting unfortunately gets re-used as this super, super common phrase.

It's standard sql behavior, users always specify the ordering they want as part of the query.

Perhaps to get better results on benchmarks.