Function rerank

src/core/reranker.ts:188–219

(query: string, results: SearchResult[])

 * Returns the full result array with the top-K portion re-ordered.
 */
export async function rerank(query: string, results: SearchResult[]): Promise<SearchResult[]> {
  if (results.length <= 1) return results;
  if (!isAmbiguous(results)) return results;

  await ensureModelLoaded();
  rerankerHealth = 'active';

  const toRerank = results.slice(0, Math.min(RERANK_TOP_K, results.length));
  const rest = results.slice(toRerank.length);

  // Score each result against the query using the cross-encoder
  const scored: Array<{ result: SearchResult; crossScore: number }> = [];

  for (const result of toRerank) {
    const passage = buildPassage(result);
    const crossScore = await scorePair(query, passage);
    scored.push({ result, crossScore });
  }

  // Sort by cross-encoder score (descending)
  scored.sort((a, b) => b.crossScore - a.crossScore);

  // Rebuild the result array: reranked top-K + unchanged rest
  // Sigmoid normalizes raw logits to [0,1] so downstream quality gating works
  const sigmoid = (x: number) => 1 / (1 + Math.exp(-x));
  const reranked = scored.map(({ result, crossScore }) => ({
    ...result,
    score: sigmoid(crossScore)
  }));

  return [...reranked, ...rest];
}