Function heavy_step 

fn heavy_step(
    here: &str,
    seal: &Seal,
    vault: &(PathBuf, [u8; 32]),
    region: Option<&Region>,
) -> bool

The part that may take a while, never inside an exchange: the history’s next batch and its media when due (import_now), and the day’s look for deletions. Under its own lock: one import at a time on the phone.