Function lift_seeded 

pub(crate) fn lift_seeded<R: Scalar + Seedable>(
    stored: &[f64],
    seed: Option<usize>,
) -> Cow<'_, [R]>

Lift stored into mode R, setting a unit tangent at seed if one is given and leaving every other parameter at a zero tangent.

The unseeded case is exactly [Scalar::lift], so the passive path still borrows: a seeded lift is a forward-mode concept and the passive scalar never reaches the owning branch.