🔀 RAG Fusion：多路检索融合技术

用户查询: "OpenClaw的MCP协议怎么配置？"
         ↓
    ┌────┴────┐
    ↓         ↓         ↓
向量检索   关键词检索   语义检索
[doc1,3,5] [doc2,3,5] [doc1,3,4]
    ↓         ↓         ↓
    └────┬────┘
         ↓
   RRF 融合排序
         ↓
   [doc3, doc5, doc1, doc4, doc2]
         ↓
   取Top-K作为上下文

// RAG Fusion实现
async function ragFusion(query, retrievers, topK = 5) {
    // 并行执行多种检索
    const results = await Promise.all(
        retrievers.map(r => r.search(query, { topK: topK * 2 }))
    );
    
    // Reciprocal Rank Fusion
    const scoreMap = new Map();
    const k = 60; // RRF常数
    
    results.forEach(retrieverResults => {
        retrieverResults.forEach((doc, rank) => {
            const score = 1 / (k + rank + 1);
            scoreMap.set(doc.id, (scoreMap.get(doc.id) || 0) + score);
        });
    });
    
    // 按融合分数排序
    return Array.from(scoreMap.entries())
        .sort((a, b) => b[1] - a[1])
        .slice(0, topK)
        .map(([id, score]) => ({ id, score }));
}