Function pin 

pub(crate) fn pin(
    qt: &CxxQtThread<Sioul>,
    shared: &Arc<Shared>,
    uid: &str,
    at: &str,
    minutes: u32,
) -> String

A task pinned to at (“2026-10-06T14:30”, your time zone) for minutes (0: as long as its block is, else what the plan lays for it): its block moved there, or made in the calendar for blocks; the task tied to it, and to it alone. Told in the status line, “Undo” offered: both put back. Returns what went wrong, else “”.