/**
 * BRAIN Vector Similarity Search
 *
 * Provides vector-based KNN search against brain_embeddings vec0 table.
 * Falls back gracefully when no embedding provider is registered or
 * sqlite-vec is unavailable.
 *
 * @task T5388
 * @epic T5149
 */
export interface SimilarityResult {
    id: string;
    distance: number;
    type: string;
    title: string;
    text: string;
}
/** Vector search outcome: the hits, or why the vector layer could not answer. */
export interface SimilaritySearch {
    /** Hits ranked by distance (ascending); empty when unavailable. */
    results: SimilarityResult[];
    /** Set when the vector layer is unavailable, naming the missing piece (T13948). */
    unavailable?: string;
}
/**
 * Search for entries similar to a query string using vector similarity.
 *
 * Returns an empty array when the vector layer is unavailable; use
 * {@link searchSimilarWithStatus} to learn why.
 *
 * @param query - Text to find similar entries for
 * @param projectRoot - Project root directory
 * @param limit - Maximum results to return (default 10)
 * @returns Array of similar entries ranked by distance (ascending)
 */
export declare function searchSimilar(query: string, projectRoot: string, limit?: number): Promise<SimilarityResult[]>;
/**
 * Vector similarity search that reports an unavailable vector layer instead
 * of returning a silent empty list (T13948).
 *
 * 1. Embeds the query text via the registered embedding provider.
 * 2. Runs KNN query against brain_embeddings vec0 table.
 * 3. Joins with observation/decision/pattern/learning tables for full entries.
 *
 * @param query - Text to find similar entries for
 * @param projectRoot - Project root directory
 * @param limit - Maximum results to return (default 10)
 * @returns The hits, plus `unavailable` when no provider, vector, extension or
 *   embedding for the active model exists, or the KNN query failed.
 * @example
 * ```ts
 * const { results, unavailable } = await searchSimilarWithStatus('worktree', root, 10);
 * ```
 */
export declare function searchSimilarWithStatus(query: string, projectRoot: string, limit?: number): Promise<SimilaritySearch>;
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