nx_isa_cf_sov.nx

nx_isa_cf_sov.nx -- CONTROL-FLOW rung: derive programs that BRANCH, run them on god. The straight-line ladder (nx_isa_equiv_sov) exercised god's ALU only. This rung exercises its CONTROL FLOW -- the PC takes a data-dependent path through a real RV64 conditional branch. (1) the team COMPOSES a random non-trivial 2-way conditional target T: result = if cmp(a,b) then ARM_then(a,b) else ARM_else(a,b) cmp in {a<b, a>=b, a==b, a!=b} (the sim's BLT/BGE/BEQ/BNE); each ARM is a 2-op chain over {ADD,SUB,MUL} ONLY -- no SLT -- so the BRANCH is the sole source of conditionality (the program is NOT expressible straight-line over this op set), (2) the team DERIVES a program G of the same shape by GA on T's TRAIN examples (sees only points), (3) ENCODE both to real RV64 machine code (a forward BLT/BGE/BEQ/BNE + a forward JAL skipping the other arm), run BOTH on rv64im_min_sim (god) over 12 HELD-OUT inputs, verify sim(T)==sim(G). B-type / J-type encoders are derived to round-trip the decoder's imm_b / imm_j (rv64im_min_decoder.nx:145-175); branch semantics match the sim's step loop (BRANCH funct3, rv64im_min_sim.nx:913-918). Controls: FAITHFUL (hand-built max / conditional programs with known answers prove the branch encoding) + NEGATIVE (a perturbed G the differential must catch). Only FORWARD branches this rung; backward branches (loops) are the next. license_tier: ORIGINAL