> I’m sure there’s a technical Unicode word for this process of matching codepoints for e.g. search and uniqueness of rendering

That’d be Unicode Normalization. I don’t have an opinion on the best source for more details, so here’s a link from unicode.org https://www.unicode.org/reports/tr15/

I don’t know enough to know whether or not there are still Arabic-specific issues, either in the spec or the implementations.

The example in the article of copy/paste/search is interesting. I think it’s equally likely to be a RtL issue as a normalization bug, but I haven’t done anything significant with either topic.