nx_h264_intra4_gate.nx

nx_h264_intra4_gate.nx -- validate Intra_4x4 (9 modes). Sovereign oracles (no 3rd party): (a) FLAT: all neighbours == C => every mode outputs C everywhere (catches out-of-bounds neighbour reads + tap coefficients that don't sum to 1). (b) mode 0 Vertical: pred[y][x]==top[x] ; mode 1 Horizontal: pred[y][x]==left[y]. (c) DDL(3): top ramp top[k]=o+s*k => non-corner pred==o+s*(x+y+1) (linear 3-tap recovery). (d) DDR(4): neighbours from g(x-y)=o+s*(x-y) => pred==o+s*(x-y) for all 16 (proven exact). Modes 5,6,7,8 (VR/HD/VL/HU) get the FLAT check here; their per-value proof is the real-frame reconstruction vs ffmpeg (capstone oracle). HONEST: stated, not hidden. Exit 0/1. license_tier: ORIGINAL