nx_bm25_gate.nx

nx_bm25_gate.nx -- INDEPENDENT GATE: integer BM25 + Reciprocal Rank Fusion, on real clause text. The teeth: u2605IDF EARNS ITS KEEP: a term appearing in EVERY document scores ZERO, so filler cannot win. A term in ONE document of four scores high -- which is how a rare defined term beats common vocabulary. u2605SATURATION: doubling term frequency does NOT double the score (k1), so keyword stuffing fails. u2605LENGTH NORMALISATION: the same term count in a longer document scores LOWER (b). u2605u2605RRF FUSES RANKS, NOT SCORES: a document ranked 1st by ONE leg beats a document ranked mid-pack by BOTH -- and an UNRANKED leg contributes nothing rather than a fabricated worst place. u2605NO FLOAT: exact at powers of two, deterministic everywhere. license_tier: ORIGINAL No hw writes (Rule 26). expect_exit: 0