/**
 * Query Expansion — LLM-based synonym / paraphrase generation for BM25.
 *
 * Natural language questions ("how does the billing flow work?") share little
 * vocabulary with card text. HyDE handles the SEMANTIC leg by generating a
 * hypothetical document and embedding it; this module handles the KEYWORD leg
 * by generating 2-3 alternative keyword-focused queries that BM25 can match.
 *
 * Results are cached in a 100-entry in-process LRU to avoid re-calling the
 * LLM for repeated identical queries (common in interactive MCP sessions).
 *
 * Falls back to an empty array (= no expansion, original query only) if:
 *   - The query is short or identifier-style (BM25 already handles those well)
 *   - The LLM is unavailable or not configured
 *   - The LLM call times out after 3 seconds
 */
/**
 * Expands a natural-language query into 0-3 alternative keyword-focused queries.
 *
 * The returned queries are intended for additional BM25 passes alongside the
 * original query. Results for all queries are merged, keeping the best rank
 * per card across all keyword searches.
 *
 * @returns Array of alternative queries (may be empty if expansion was skipped).
 */
export declare function expandQuery(query: string): Promise<string[]>;
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