nx_shard_query.nx

nx_shard_query.nx -- LIB: sharded SCATTER-GATHER query = the distributed READ PATH that makes the index scale horizontally to petabytes. The index is partitioned into shards (by host/hash -- nx_shard); a query fans out to ALL shards, each returns its LOCAL top-k, and the coordinator MERGES the per-shard top-k into the GLOBAL top-k. EXACT by invariant: a doc in the global top-k must be in its own shard's top-k (a shard can't hide a global winner in its local top-k), so merging (nshards*k) candidates and taking top-k is identical to a single whole-corpus index. Built + gated NOW on a fixture; the network fan-out + parallel shard servers run on the NAS/cluster later. No float. license_tier: ORIGINAL