nx_doccount_gate.nx

nx_doccount_gate.nx -- THE CORPUS-SIZE FAST PATH, PROVEN AGAINST THE WALK ON THE LIVE SHARD (search L5, 2026-09-14). WHY. idf needs N, the number of doc: keys across the live segments. ss_doc_count used to WALK every .keys entry of every segment on every query; the phase timers measured that at 324 ms of a 331 ms prep, on every query, warm or cold -- 98 percent of prep and the largest cold term left after L0 and L3. The cut: each row carries its own count from load time in its aux row (ss_doccount_build, one predicate ss_is_doc_key shared with the walk) and ss_doc_count sums them, falling back to the walk when any row lacks one. Ranking is byte-identical only if the sum IS the walk, so this gate opens the REAL shard and asserts that -- plus a poisoned-row neg-control that proves the fast path is what answers, and a cleared-row neg-control that proves the fallback still answers. license_tier: ORIGINAL No hw writes (Rule 26).