Function merge_curve_continuation_edges 

pub fn merge_curve_continuation_edges(
    solid: &BrepSolid,
    tolerance: f64,
) -> Result<BrepSolid, String>

Collapse tangent continuation edges seen by the same two incident faces — or by the same face TWICE, which is what a split seam looks like.

Both 3D curves and both face p-curves are concatenated exactly. Periodic branch changes are rejected if they alter either face’s parameter area.