nx_zstd_fse_gate.nx

nx_zstd_fse_gate.nx -- proves the FSE (tANS) decoding-table build. An FSE table is not verifiable by eyeballing one cell -- it is verifiable by its INVARIANTS, and those invariants are exactly what a bad spread breaks: * every cell receives a symbol (a stride that is not coprime with the table size silently overwrites cells and leaves holes) * each symbol occupies exactly its normalized count of cells * nb_bits and new_state stay inside the table T4/T5 are the ones that catch the classic defect: with table_log 3 the stride is 8 and 8 & 7 == 0, so the walk never advances and one symbol eats the whole table. We refuse that log outright, and T9 proves it. NON-VACUITY: T8..T12 are negative controls -- counts that do not fill the table, a log below the minimum, a log above the maximum, and out-of-range state lookups must each be REFUSED. license_tier: ORIGINAL