Function fetch_wanted_into_copy 

fn fetch_wanted_into_copy(
    server: &Server,
    memory: &Path,
    folder: &Path,
    (own, account): (&str, &str),
    (key, frugal): (&[u8; 32], bool),
    now: i64,
    url: &dyn Fn(&str) -> String,
    pulled: &mut Pulled,
) -> Result<(), SyncError>

The sealed files this device waits for (wanted_in_copy), fetched by their names into its copy (sealed_step): the smallest first, 64 MiB at most a step (the first whatever its size), as long as the step’s time lasts; on a metered or slow connection (frugal), one of SMALL_WANTED or more at most every ten minutes. Each kept only once it opens whole to its content (blobs::check), put in its place under the step’s lock some at a time (place_fetched). One not there, cut, or that does not open, asked again after its backoff: within five minutes in its first hour (a sync app still sending it), then less and less often. who: this device’s id, and the account.