nx_imgsearch_engine.nx

nx_imgsearch_engine.nx -- THE MULTI-TIER REVERSE-IMAGE QUERY ENGINE. Replaces the shipped single-tier client (nx_image_search) on two counts, both of them load-bearing: 1. IT SCALES. The shipped client ranks by scanning every fingerprint and then SELECTION-SORTING the whole corpus -- O(N^2). At 1,000 images that is a million comparisons; at the 10^6 an indie image index reaches it is 10^12 and the query never returns. Here every tier extracts its top-K through a BOUNDED MAX-HEAP of size K: O(N log K) time and O(K) space, with N touched exactly once. Going from 10^3 to 10^6 images multiplies the work by 10^3, not 10^6. 2. IT FUSES. One descriptor cannot cover the modification space (nx_imgbench proves it class by class), so the engine runs every registered tier and combines their ranked lists with RECIPROCAL RANK FUSION -- score = sum over tiers of weight / (K_RRF + rank). RRF is the fusion the S-Class IR literature settles on precisely because it needs no score calibration between rankers: a Hamming distance over 64 bits and an L1 distance over 80 dimensions are never comparable as magnitudes, but their RANKS always are. Same integer discipline as the text engine -- no floats anywhere. The engine holds only base-class tier pointers. Adding local-feature or semantic matching is a new nx_imgtier subtype plus one add_tier call; this file does not change. That is the design contract. genealogy_id: cormack_2009_reciprocal_rank_fusion + williams_1975_bounded_heap_selection license_tier: ORIGINAL