Function hold_may_release 

pub fn hold_may_release(
    view: &FootprintView,
    unit: &UnitId,
    invocation: Option<&str>,
    now: u64,
) -> bool

The hold’s condition on a failure, as lane-nix’s script implements it (crate docs, “The hold’s order”): it may release only when the unit’s footprint describes the invocation that failed (invocation, systemd’s InvocationID), that invocation has ended (its cgroup is gone and the ring drained after, so nothing it did is still to come), and the footprint reads protecting no at now, with nothing unattributed. Anything else holds. The reference the property tests check.