nx_av1_txfm2d_gate.nx

nx_av1_txfm2d_gate.nx -- proves the 16 2-D transform types are a BIJECTION onto the 4x4 grid of 1-D kinds, and that FLIPADST really flips. T1 IS THE HEADLINE. AOMedia's own AV2 overview says AV2 reuses "four primary 1-D transform types producing 16 2-D combinations" from AV1 unchanged. That sentence is a testable claim, so it is tested: build a 4x4 occupancy grid from (col_kind, row_kind) over all sixteen types and assert every cell is hit EXACTLY once. Any single mis-assignment double-books one cell and empties another, so the check catches a one-type error, not just gross breakage. T3 pins the AV1 naming convention -- first token is the COLUMN. Swapping it yields a transposed error that decodes cleanly on symmetric content and only shows on directional detail, which is the worst kind of bug to ship. T5/T6 are non-vacuity: an unknown type must return -1 rather than defaulting to DCT, and the 1-D dispatcher must REPORT that it did nothing rather than quietly leaving a plausible block behind. license_tier: ORIGINAL