Certified critical-line bound 0.673581220187184030948043414065

Builds on Samuel Lavery’s attempt-021 (nine-point checker and counting chain, generic in n) and R. Arun Chandru’s master-of-puppets5 (Gram-defect chain), whose code is kept unchanged outside the regenerated certificate segments; the modification notice is in the file. Weights re-optimised under the checker’s symmetry constraints; 10,937 checked leaves; cN = 859538456469471854.