/**
 * Atomic filesystem helpers — the single source of truth for durable
 * config/session writes across `@a5c-ai/agent-mux`.
 *
 * Guarantees:
 *  - Writes are atomic: a concurrent reader observes either the old or the
 *    new bytes, never a torn intermediate.
 *  - Writes are durable: data + directory entry are fsynced before rename.
 *  - Concurrent writers serialise through an advisory lockfile (`<path>.lock`)
 *    which records the holder's PID and a monotonic timestamp. Stale locks
 *    (holder dead or older than `staleMs`) are forcibly reclaimed.
 *
 * These primitives have no runtime dependencies beyond Node built-ins and
 * work identically on Windows, macOS, and Linux.
 *
 * @see docs/08-config-and-auth.md
 */
export interface AtomicWriteOptions {
    /** Acquire an advisory lock before writing. @default true */
    readonly lock?: boolean;
    /** Max time to wait for a lock, in ms. @default 5000 */
    readonly lockTimeoutMs?: number;
    /** Lock is considered stale after this many ms without refresh. @default 30000 */
    readonly staleMs?: number;
    /** fsync the file after write. @default true */
    readonly fsync?: boolean;
    /** File mode for writeFile. */
    readonly mode?: number;
}
/** Write `data` to `filePath` atomically (tmp + fsync + rename). */
export declare function writeFileAtomic(filePath: string, data: string | Uint8Array, opts?: AtomicWriteOptions): Promise<void>;
/** Write `data` as pretty-printed JSON atomically. */
export declare function writeJsonAtomic(filePath: string, data: unknown, opts?: AtomicWriteOptions): Promise<void>;