async fn resolve_default_branch(cwd: &Path, budget: Duration) -> Option<String>Expand description
Resolve the ref a feature branch’s “ahead” diff compares against.
Prefers the remote-tracking origin/<default> (via origin/HEAD,
else origin/main / origin/master) so a locally-stale main
can’t fold already-merged commits into the diff; falls back to a
purely-local main / master for a repo with no origin remote.
The returned value IS the compare-ref - the origin/ prefix carries
the remote-vs-local decision, so callers wanting the plain branch
name strip it. None when nothing resolves.