nx_av1_txfm_gate.nx

nx_av1_txfm_gate.nx -- proves the AV1/AV2 transform primitives. T1 pins the DIFFERENCE between Round2 and Round2Signed on negatives. They agree on non-negative input and diverge below zero: Round2(-3,1) is -1, Round2Signed(-3,1) is -2. Substituting one for the other yields a transform that is correct on a test pattern of positives and half-wrong on real signal. The gate asserts the divergence explicitly rather than testing each in isolation, because testing them separately is exactly what lets the substitution survive. T4 pins the cosine table's QUADRANT SIGNS. Only angles 0..64 are stored; the rest are reflections. A wrong sign in one quadrant inverts half the basis functions and decodes to a recognisable-but-wrong image -- it does not look like noise, so it ships easily. The test walks all four quadrants and asserts the Pythagorean identity holds at 12-bit precision throughout. T5 round-trips the Walsh-Hadamard pair over pseudo-random vectors -- the lossless path must be EXACTLY invertible, not approximately. license_tier: ORIGINAL