1-of-N shares are not supported

I think this was implicitly acknowledged in #10, but one cannot create 1/2 or 1/3 etc because it ends with a zero share identify (or whatever the phrasing is).

Is this a known constraint, i.e. `1` of `N` shares are explicitly disallowed, and `1` of `1` was added as an exception? Or is this a bug?

Look at the code handling share creation, likely in a module like dkg.rs or share.rs. The issue mentions #10 for context. Check the validation logic for share identities, especially around zero values. Run existing tests related to share creation to see if 1-of-N cases are covered. The fix will involve adjusting the validation to allow 1-of-N shares while maintaining security properties.

索引モデルが issue の本文から書いたものです。