nx_dd_verify.nx

nx_dd_verify.nx -- the DD-PRIMITIVE CONTRACT VERIFIER (ONE-STEP-TEN-SECOND tool for the dd-composition bug class). The gamma dd probe hit a ~5e11-ulp STRUCTURAL bug from using _sh_mul2/_sh_2sum/_sh_expdd without verifying their hi/lo output contract. Instead of hand-debugging twice, this organ is the TEAM's one-command answer: it runs each dd primitive on KNOWN double-double values, PRINTS the actual contract (which slot is hi, which is lo, what 2^n means), and gates the round-trip. Run it before ANY dd composition -> the contract is known, the class is retired. KATs (error-free-transform identities, exact): _sh_2sum(a,b) : out[0]=round(a+b), out[1]=exact error; out[0]+out[1]==a+b _sh_mul2(a,b) : out[0]=round(a*b), out[1]=exact error; out[0]+out[1]==a*b _sh_expdd(v) : exp(v)==(out[0]+out[1])*2^out[2] (the scale contract) Durable: DDVERIFY rows (with the OBSERVED slots) + DDGATE -> knowledge/status/ dd_verify.log. Exit 0 = all contracts hold. license_tier: ORIGINAL