Function montgomery_reduction_divisibility 

pub fn montgomery_reduction_divisibility() -> bool

Certify the Montgomery DIVISIBILITY: x + (x·qinv')·q = x·169·R, i.e. the reduction’s numerator (with the un-reduced lo = x·qinv') is an EXACT multiple of R — so redc’s / R is an exact shift, never a rounding division. This is what makes qinv' = 3327 the RIGHT constant (qinv'·q ≡ −1 mod R): the kernel ring canonicalizer reduces both sides to x·11075584, certifying it for ALL x, not a sampled width.