export type LockResult<T> = {
    result: T;
    next?: string;
};
/** Throws if this lock was compromised (stolen/expired) since acquisition. Callers that write
 *  from INSIDE the critical section must call it immediately before that write, because the
 *  post-`fn` check cannot un-write a file the callback already replaced. */
export type LockHeldGuard = () => void;
export interface LockedFileBackend {
    withLockAsync<T>(fn: (current: string | undefined, assertLockHeld: LockHeldGuard) => Promise<LockResult<T>>): Promise<T>;
    /** The current whole-file contents, or undefined when the file does not exist yet.
     *  Lock-free: every writer replaces the file by atomic rename. */
    readUnlocked(): string | undefined;
}
/** A 0600 JSON file guarded by a cross-process `proper-lockfile` lock on its own path. */
export declare class LockedJsonFile implements LockedFileBackend {
    private readonly path;
    constructor(path: string);
    readUnlocked(): string | undefined;
    private ensureFile;
    /** Acquire the lock without blocking the event loop, keeping every read-modify-write
     *  callback on the same asynchronous path. */
    withLockAsync<T>(fn: (current: string | undefined, assertLockHeld: LockHeldGuard) => Promise<LockResult<T>>): Promise<T>;
}