Reading HEAD is worth keeping for the repos it can answer for, because
the menu opens on a keystroke and asking git costs a process per entry.
So go to git only for the placeholder, and for anything else the read
can't make sense of. That last part also gets the menu an answer for
layouts we don't know about yet, where it used to give up and say
"Branch unknown".
Git needs two commands to cover every repo. `git symbolic-ref` names the
branch even when it has no commit yet; `git rev-parse` resolves a
detached HEAD, and fails on a branch without a commit.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>