> The remaining pending decisions are "feis[s], geis[s]ib,
> tres[s]". These all qualify for Thurneysen's class of 's'
> "between stressed short vowel and another vowel, and also in
> final position after a stressed short vowel", the environments
> where 'ss' was commonly written. So I'll write 'ss' in all
> three cases, right?
Yes, that's fine.
> As for "chois, fris", should we rethink the final single 's'?
Well, we could try to harmonise them with other words with short stressed vowels, i.e. "choiss, friss..."