hspow: Scheme ordering. Duplicate unknown schemes

An hsdesc inner doc can contain something like this:

pow-params wombat ...
pow-params v1 ...
pow-params wombat ...

The spec says this may appear "at most once per scheme". Is the client supposed to check this for unknown schemes? If so it would need to build a data structure of strings, solely to perform that check.

Does it matter that the ordering isn't specified?

If we said the ordering was ASCII lexical on the scheme name, duplicates could be detected without a proper data structure.

IHNI what C Tor does.

Apropos of my review of arti!2026 (closed). Whatever answer we come up with should be implemented in C Tor and in Arti.