pub fn p2_cond_from(p1: f64, mean_na: f64) -> Option<f64>Expand description
2026-09-25: The second-draft conditional accept implied by a flush at two
drafts, where mean_na = p1 + p1*p2_cond: (mean_na - p1) / p1, clamped
to [0, 1]. Deeper drafts are not modelled. None when p1 <= 0.