Internal adversarial pass, not an independent review. Adds the cube-sum
(higher-order differential) command to bound the algebraic degree of the
applications: a low degree would admit a cheap polynomial batching of the 8
applications, so degree saturation at small d is the no-shortcut bound. Plan
section 8 records main's three-lane re-scope: this lane is the algebraic
structure of M_r.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>