Function resolve_ref_format_with 

pub fn resolve_ref_format_with(
    context: &GitContext,
    cwd: &Path,
    snapshot: Option<&ConfigSnapshot>,
) -> Result<RefFormat, GitFailure>

What: Reads the ref storage backend, from the configuration snapshot when it proves files. Why: rev-parse --show-ref-format prints reftable only for a repository whose configuration names extensions.refStorage, so a snapshot read without global options that has no such key proves files without starting Git; any other snapshot, and a missing one, asks Git.

In TS you’d write (pseudocode):

snapshot?.provesFilesRefStorage() ? 'files' : await resolveRefFormat({ gitPath, cwd });