PluginSourceGit.sync() raises AttributeError in its branch-resolution fallback because it accesses repo.branches.local, but the GitRepository abstraction exposes no branches attribute.

The fallback path (HEAD unset and no main branch) uses repo.branches.local. GitRepository only offered an Any-typed get_branches() passthrough to the raw pygit2 Branches object, so:

• the wrong attribute crashed at runtime instead of resolving a branch;
• because the return type was Any, ty could not catch the mistake statically.

Possible solution

• Replace get_branches() -> Any with a typed, backend-agnostic branch API on GitRepository: local_branches() -> list[str] and create_tracking_branch(name, commit_id, upstream).
• Migrate both call sites (plugin3/plugin.py fallback, git/ops.py switch-branch) off the raw pygit2 object; ops.py no longer touches repo._repo.
• Add a regression test that drives sync() into the fallback state and fails on the pre-fix code.