nx_av1_adst_gate.nx

nx_av1_adst_gate.nx -- proves the inverse ADST and its distinctness from DCT. T1 is exact and needs no reference vectors: a basis-0 impulse of 4096 must return the four SINPI constants themselves, in order -- [1321, 2482, 3344, 3803]. Any wrong constant, any mis-wired term, any wrong rounding shift moves at least one of them. T2 is the property that says WHY the ADST exists: its basis-0 output is a RISING RAMP, where the DCT's is FLAT. The gate runs the same impulse through both transforms and asserts the DCT gives four equal values while the ADST gives four strictly increasing ones. Substituting one for the other decodes without error and produces wrong gradients at block edges -- banding, not corruption -- so proving they DISAGREE is the point. T4 pins the per-axis transform-type selector. AV1 picks independently for rows and columns; swapping the axes yields a transposed-looking error that survives on square symmetric content and breaks everything else. license_tier: ORIGINAL