nx_livemap_fast_gate.nx

nx_livemap_fast_gate.nx -- prove the LINEAR live-doc map is byte-identical to the quadratic one. ss_open2 already built the authoritative maps at h[1 + 8*ns + s] using the existing O(keys x segments) shadow scan. This gate rebuilds the same maps using the newest-first hash table from nx_livemap_fast and compares EVERY BYTE. Any difference is a correctness failure, not a perf note: these maps decide which documents are visible, so a faster map that is subtly different does not make search quick, it makes search WRONG. Run against the REAL shard, not a fixture. A synthetic 2-segment store would not exercise the shadow logic that only appears with many overlapping segments, and this session already learned that a gate is only as honest as its ugliest input. license_tier: ORIGINAL No hw writes (Rule 26).