Function open_selected 

pub fn open_selected(
    root: &Path,
    account: &str,
    hash: GitHashKind,
    arms: StoreConfig,
) -> Result<SelectedStore>

Open a store with all three arms chosen at run time.

The one place crate::arms::IndexArm — a value — is turned into S — a type. See SelectedStore for what the resulting handle costs.