nx_image_index_gate.nx

nx_image_index_gate.nx -- referee for the REAL-CORPUS ingestor (nx_image_index). Unlike the search gate (synthetic raw-gray buffers), this builds REAL encoded PNG files at runtime (valid signature + IHDR + zlib stored-block IDAT + IEND, with chunk CRC-32s and the zlib Adler-32 computed by the shipped substrate primitives -- same technique as nx_png_real_smoke), writes them to /tmp, forks+execs the REAL /tmp/nx_image_index.sov.elf over them, and verifies the produced fingerprint index. Because each PNG is filled RGB=(v,v,v), Rec.709 luma == v, so the FULL decode path (inflate -> unfilter -> RGB -> gray -> dHash) must reproduce the KNOWN dHashes proven in the search gate -- a true end-to-end KAT, checkable by pure string match: row1 grad-up -> dHash 0000000000000000 (decode->gray->dHash correct, end to end) row2 +bright -> dHash 0000000000000000 (brightness invariance survives a real PNG round-trip) row3 grad-down -> dHash ffffffffffffffff (second KAT, opposite extreme) row4 mid -> present and DISTINCT from grad-up row5 corrupt -> SKIPPED (graceful degradation, Cardinal 14 -- one bad file can't abort a crawl) row6 summary -> ingestor exit 0, indexed=4 skipped=1 GREEN iff 6/6. Durable verdict appends to knowledge/status/image_index_gate.log. license_tier: ORIGINAL