- the tangent scatter runs per CSR entry over a transposed contribution
map, in the serial scatter's order (same bits), on rayon;
- large fronts' trailing gemms run per column block on rayon;
- forward solve multifrontal, backward top-down, subtrees on rayon;
- total_lagrangian::internal_force: the force of internal_force_and_tangent
alone (bit-identical, tested), used by modified-Newton iterations that
reuse the factor; the tangent is evaluated only when a refresh is due.
Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
