Function scheduled_delivery_visible 

pub fn scheduled_delivery_visible(
    scheduled: bool,
    uncertainty_ms: i64,
    activation_ms: i64,
    now_ms: i64,
) -> bool

Decide whether a record batch may be exposed at the supplied clock reading.

A negative uncertainty is invalid and fails closed for scheduled delivery. A deadline that cannot be represented also fails closed instead of becoming visible early through saturating arithmetic.