/**
 * Acquire an advisory lock on the accounts directory. Blocks (busy-wait
 * with sleep) until the lock is free or `timeoutMs` elapses.
 *
 * Returns a release function. Always call it in a finally block.
 */
export declare function acquireLock(accountsDirPath: string, timeoutMs?: number): () => void;
/**
 * Run `fn` while holding the accounts lock. Releases on both success and error.
 */
export declare function withLock<T>(accountsDirPath: string, fn: () => T): T;