Function step_credit 

fn step_credit<R: Scalar>(
    grid: &TimeGrid,
    face_at: impl Fn(NaiveDate) -> f64,
    view: &PricingView<'_, R>,
    product: &'static str,
) -> Result<StepCredit<R>, PricingError>

The view’s credit on grid’s steps, recovering on face_at — the same refusals as risky_on_view for a missing curve or recovery.