/**
 * File storage utilities — saving binary files to disk,
 * directory cleanup, and maintenance flag management.
 *
 * Extracted from config.ts during modular decomposition (phase 1).
 */
export declare const FILES_DIR: string;
/**
 * Save a buffer to disk under FILES_DIR with a unique timestamped name.
 * Returns the absolute file path. Caps directory at 500 files by deleting oldest.
 */
export declare function saveFileToDisk(buffer: Buffer, filename: string): string;
/**
 * Write the current epoch timestamp to a heartbeat file.
 * The update watcher checks this before force-killing the server —
 * if a tool call happened recently, the kill is deferred.
 */
export declare function writeActivityHeartbeat(): void;
/** Write epoch timestamp for a specific thread. Called on every MCP tool call.
 *  Uses atomic write (tmp + rename) to prevent keeper from reading a truncated
 *  file, with retry + direct-write fallback so a transient Windows lock can't
 *  silently drop the heartbeat (a dropped heartbeat risks a false "stuck"). */
export declare function writeThreadHeartbeat(threadId: number): void;
/** Synchronous heartbeat write — guarantees the file is flushed before returning.
 *  Used at spawn time and in the poll loop to prevent false zombie detection. */
export declare function writeThreadHeartbeatSync(threadId: number): void;
/** Read the last heartbeat epoch for a thread. Returns null if no heartbeat. */
export declare function readThreadHeartbeat(threadId: number): number | null;
/** Delete a thread's heartbeat file. Called when a tracked process exits so a
 *  stale (spawn-time or last-activity) heartbeat can't make a dead thread look
 *  alive — which would otherwise block the keeper's restart. A live worker that
 *  is still serving the thread simply rewrites the heartbeat within ~2s. */
export declare function clearThreadHeartbeat(threadId: number): void;
/**
 * Check if a maintenance/update is pending.
 * The update watcher writes this file before restarting the server.
 * Returns the flag file content (version info) or null if no maintenance pending.
 *
 * If the flag is older than 5 minutes it is assumed stale (the update watcher
 * failed to clean it up) and is automatically deleted.
 */
export declare function checkMaintenanceFlag(): string | null;
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