Function corroboration_boost 

pub fn corroboration_boost(
    score: f32,
    distinct_sessions: usize,
    weight: f32,
) -> f32

Corroboration ranking boost — monotone, bounded, saturating.

factor = 1 + weight * n/(n+2) over the distinct-session count n: uncorroborated passes through (factor 1.0 at any weight), the first corroboration moves most (+w/3), later ones diminish toward the 1+w ceiling. Weight 0.0 (the default) disables weighting entirely.