Repository default branch is immutable after the first push

[HolgerHatGarKeineNode]

A repository's default branch (HEAD) is fixed by whatever the first push creates, and there is no supported way to change it afterwards.

Repro

git push buzz HEAD:main        # local branch is actually `master`
git push buzz master relaunch-b
git push buzz --delete main
# remote: error: refusing to delete the current branch: refs/heads/main

The repo is now stuck advertising HEAD -> refs/heads/main, a branch that does not exist locally.

Why no client can fix it

• init_bare_repo hardcodes symbolic-ref HEAD refs/heads/main (hydrate.rs:183), so the first push always starts from main.
• Every subsequent hydration rewrites HEAD from the manifest (hydrate.rs:369), so a server-side git symbolic-ref does not survive — and run_git deliberately isolates $HOME, so receive.denyDeleteCurrent cannot be configured either.
• The desktop client reads the default branch from the kind:30618 HEAD ref and has no write path for it (hooks.ts:205-212).
• buzz repos create cannot rewrite it, and there is no repos rm (No way to delete a repo announcement (kind:30617): CLI has no repos rm, and Desktop 'Delete project' is owner-gated to keys the app holds #2326) to start over.

Workaround

Delete the manifest pointer in object storage, then push the intended default branch first:

mc rm loc/<bucket>/repos/<community>/<owner>/<repo>/pointer
git push buzz master        # HEAD now resolves to refs/heads/master
git push buzz relaunch-b

Re-publishing the kind:30617 announcement re-seeds the pointer, so this does not require deleting the repo. Note that a repo whose pointer is missing returns 404 repository not found even for git-receive-pack, because info_refs_subprocess uses hydrate_for_read for both services (transport.rs:726).

Expected

Either a way to set the default branch (CLI flag, kind:30617 tag, or desktop setting), or resolve_published_head honouring a delete of the current HEAD branch when other branches remain.

Buzz 0.4.26, self-hosted relay ghcr.io/block/buzz:main.