Function put_back 

pub fn put_back(
    memory: &Path,
    vault: Option<(&Path, &[u8; 32])>,
    stores: &[Store],
    part: &str,
    file: &str,
    stamp: &str,
    now_ms: i64,
) -> Result<(), String>

A version put back (history). A file whole goes back as it was, the file as it is now kept first. A file of entries (settings, lists, the doses’ record, sessions) is put back entry by entry: each entry the version held goes back to what it was, those taken out since come back, and those added since stay. Putting back never takes out, on any device, what was added after that version. The next exchange sends what changed as changes made here, dated now. stores holds every part, those switched off too (a part off here is put back here only); vault the sharing folder and its key, for a version kept by reference. Waits for an exchange running.