/**
 * Reciprocal Rank Fusion (Task 308).
 *
 * Replaces the weighted-sum fusion (`0.7 * vector + 0.3 * bm25_norm`) when
 * the `MAXY_GS_RRF` flag is on. RRF is robust to score-distribution drift
 * between the vector and BM25 indexes — it sums `1 / (k + rank_i)` for each
 * node across the ranked lists it appears in. Higher rank (lower index) →
 * larger contribution; the constant `k` (default 60, per the gbrain
 * default) smooths the long tail.
 *
 * The weighted-sum baseline stays as the fallback so flag flips are
 * reversible without code edits.
 */
export interface FusionCandidate {
    nodeId: string;
}
/**
 * Fuse multiple ranked lists by Reciprocal Rank Fusion.
 *
 * Each input list is treated as already sorted (best first). For each
 * candidate, score = sum over lists of `1 / (k + rank)`. Returns the union
 * sorted by descending RRF score.
 *
 * Ties on RRF score are broken by the candidate's earliest appearance
 * across the input lists (first-seen wins), which is deterministic given
 * a deterministic input order.
 */
export declare function fuseRrf<T extends FusionCandidate>(rankedLists: T[][], k?: number): Array<T & {
    rrfScore: number;
}>;
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