/** Minimal structural types for node:sqlite (still marked experimental). */
export interface SqliteStatement {
    run(...params: unknown[]): {
        changes: number | bigint;
    };
    get(...params: unknown[]): Record<string, unknown> | undefined;
    all(...params: unknown[]): Record<string, unknown>[];
}
export interface SqliteDatabase {
    exec(sql: string): void;
    prepare(sql: string): SqliteStatement;
    close(): void;
}
export declare const SQLITE_SCHEMA_VERSION = 2;
/** Probe whether node:sqlite is available on this runtime. */
export declare function sqliteAvailable(): boolean;
/**
 * Open (creating if needed) the project database and apply the schema.
 * Throws when node:sqlite is unavailable — callers should probe first.
 */
export declare function openDatabase(twiningDir: string): SqliteDatabase;
/**
 * Run a read-modify-write cycle inside an IMMEDIATE transaction.
 * WAL serializes individual statements, not statement PAIRS: two processes
 * can both SELECT the same row and the second UPDATE silently clobbers the
 * first's merge — a lost-update race the multiwriter soak reproduces.
 * BEGIN IMMEDIATE takes the write lock up front (waiting on busy_timeout),
 * making the whole cycle atomic across processes.
 */
export declare function withWriteTxn<T>(db: SqliteDatabase, fn: () => T): T;
/**
 * Serialize a float vector to a BLOB (little-endian float64 — exact
 * round-trip parity with the JSON file backend; float32 would silently
 * perturb similarity scores across backends).
 */
export declare function vectorToBlob(vector: number[]): Uint8Array;
/** Deserialize a BLOB back into a float vector. */
export declare function blobToVector(blob: Uint8Array): number[];
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