sketch_hash_map.nx

sketch_hash_map.nx -- open-addressing hash map (i64 -> i64). Foundational data-structure primitive. Linear-probing open-addressing with power-of-2 capacity and 70%-load resize trigger (v1: no resize -- caller sizes correctly). Stores (key, value) pairs where key != 0 (zero reserved as empty sentinel). API: nx_hmap_put(m, key, value) upsert nx_hmap_get(m, key) return value or 0 if absent nx_hmap_has(m, key) 1 or 0 nx_hmap_remove(m, key) delete; returns 0/-1 nx_hmap_size(m) active entries nx_hmap_clear(m) empty without freeing Many sketches in this branch use ad-hoc linear-probe hash tables (HllMap, LossyCounting, etc.). Promoting this to a sovereign primitive lets future sketches compose against it instead of re-implementing. Production tier, exact semantics. No envelope returned. DELETION: tombstone-based. Removed slots stay marked with a special sentinel until the next put rebuilds the chain. This keeps lookups O(1) average without rehashing.