/**
 * L3 — Reciprocal Rank Fusion. Merges N ranked `RetrieveHit` lists into
 * one, scoring each id by Σ 1/(k + rank) across the lists it appears in. Pure,
 * deterministic, no I/O — which is why it serves BOTH hybrid lexical⊕semantic
 * fusion AND klum-db's cross-vault federation (the lists are per-vault). The
 * fused `score` is the RRF score, NOT BM25 or cosine.
 */
import type { RetrieveHit } from './retrieve-types.js';
export interface FuseOptions {
    /** Only 'rrf' in v1 (default). */
    readonly strategy?: 'rrf';
    /** RRF constant; larger flattens the rank weighting. Default 60. */
    readonly k?: number;
    /** Truncate the fused output to this many hits. */
    readonly limit?: number;
}
/**
 * Callers must supply hits with `rank >= 1` (the retrieve contract guarantees
 * it; a federation caller passing `rank: 0` with `k: 0` would divide by zero).
 * Doc-only note — no runtime guard; rank ≥ 1 is the retrieve contract.
 */
export declare function fuseRetrieval<T>(lists: ReadonlyArray<ReadonlyArray<RetrieveHit<T>>>, opts?: FuseOptions): RetrieveHit<T>[];