fix: Honor updateRef when creating signed commits

[VedantMadane]

Summary

Honor updateRef when creating signed commits

Changes

• After commit_signed, update the named ref (create or set_target)
• Matches unsigned commit() behavior so signed commits are not unreachable

Fixes #218

[vercel]

@VedantMadane is attempting to deploy a commit to the Toss Team on Vercel.

A member of the Team first needs to authorize it.

[marshallku]

Thanks for taking this on, and sorry for the slow response.

Unfortunately this doesn;t fix #218 as written. Repository::find_reference is git_reference_lookup, which does not resolve symbolic references. HEAD is symbolic in a normal repository, so set_targe hits libgit2's ensure_is_an_updatable_direct_reference() and fails with cannot set OID on symbolic reference. I reproduced it against the pinned git2 =0.20.4:

So updateRef: 'HEAD' — the exact case in #218 — goes from a silent no-op to a thrown error, and the existing create signed commit test (tests/commit.spec.ts:67) plus the documented example in docs/usage/commit.md:54 would both break. CI hasn't run on this branch yet, so it hasn't surfaced.

The primitive libgit2 uses here is git_reference_lookup_resolved (git2: find_reference(name)?.resolve()), and its unsigned path also validates the first parent against the current tip before writing the object. #225 implements that with tests, so I'm closing this in favour of it.

Thank you for the effort regardless — please do keep an eye on the issue list.