Function checked_attachment 

fn checked_attachment(
    qt: &CxxQtThread<Sioul>,
    shared: &Arc<Shared>,
    key: String,
    index: i32,
    afterwards: Afterwards,
    unchecked: bool,
)

Writes an attachment to the cache, has the antivirus check it, then opens or saves it; a threat, or no antivirus, and the copy is deleted. On a phone, which has no antivirus Sioul can call, nothing is scanned and nothing claims it: the attachment opens in the app you choose, or Android asks where to save it (attachments).