Function rollback 

pub fn rollback(
    run: &mut Run<'_>,
    discard_unreadable: bool,
) -> Result<Option<Vec<Refusal>>, MigrateError>

What: The rollback. Ok(None) means it ran; Ok(Some(refusals)) means nothing was changed. Why: Three states can be undone: before the exchange (delete the new subvolume and the lock), after it (carry back, swap again, delete the new subvolume), and in between (finish the bookkeeping, then the second case).

In TS you’d write (pseudocode):

const refused = await rollback(run);