nx_param_joint.nx

nx_param_joint.nx -- X-PRM-004 (PRMJOINT-pairs-swept): the JOINT pair-sweep rung for COUPLED knobs. The terrace lesson (params.tsv procgen_coupled_knobs): greedy single-variable tuning ZEROES peaks that are only reachable by moving two coupled knobs TOGETHER -- coordinate ascent stalls on the terrace because every single-knob step from the start goes DOWN into the coupling valley. This organ is the generic pair-sweep harness + the proof: POS (coupled): a terrace fitness whose peak (a>=H AND b>=H)=100 sits behind a valley (single moves =5 < start=10). JOINT grid-sweep finds 100; GREEDY coordinate-ascent stalls at 10. joint_wins = (coupled_joint > coupled_greedy). NEG (separable): f=a+b has NO coupling, so greedy is already optimal -- JOINT must NOT beat it (no_false_win = (sep_joint == sep_greedy)). Proves the harness only claims a win on REAL coupling, never a spurious one. Honest scope: the fitness here is a synthetic terrace MODEL of coupled knobs (capability proof); wiring the live grader WIN floor as the fitness is the follow-on (cf. nx_param_tune rung2 note). Sovereign (nx_cc->nxasm_x86, no gcc). license_tier: ORIGINAL