/**
 * FileSystemCheckpointStore — persistent checkpoint storage on disk.
 *
 * Stores checkpoint data as JSON arrays in `.rolebox/state/checkpoints/{task_id}.json`,
 * one array per task (supporting multiple checkpoints per task).
 *
 * Uses the same atomic write pattern (.tmp + renameSync) as TaskStateStore
 * and MetricsPersister to prevent file corruption from partial writes.
 */
import type { CheckpointData, CheckpointStore } from "../types.checkpoint.ts";
/** Maximum checkpoints retained per task. Older entries are evicted (FIFO). */
export declare const MAX_CHECKPOINTS_PER_TASK = 100;
export declare class FileSystemCheckpointStore implements CheckpointStore {
    private directory;
    /**
     * @param directory  Base workspace directory (usually process.cwd()).
     *                   Checkpoints are stored under `.rolebox/state/checkpoints/`.
     */
    constructor(directory: string);
    /**
     * Append a checkpoint to the task's checkpoint array and persist to disk
     * atomically (tmp file + rename).
     */
    saveCheckpoint(taskId: string, data: CheckpointData): Promise<void>;
    /**
     * Read all checkpoints for a task and return the most recent (by created_at),
     * or null if none exist.
     */
    getLatestCheckpoint(taskId: string): Promise<CheckpointData | null>;
    /**
     * Read all checkpoints for a task, sorted by created_at (newest first).
     */
    listCheckpoints(taskId: string): Promise<CheckpointData[]>;
    /**
     * Delete the checkpoint file for a task.
     * No-op if the file does not exist.
     */
    deleteCheckpoint(taskId: string): Promise<void>;
    /**
     * Scan all checkpoint files, remove entries whose (created_at + ttl_ms)
     * is in the past relative to `now`, rewrite files that have remaining
     * entries, and delete files that become empty.
     *
     * @param ttlMs  Time-to-live in milliseconds. Entries older than
     *               (now - ttlMs) are removed. When ttlMs <= 0, all are expired.
     */
    cleanupExpired(ttlMs: number): Promise<void>;
    /**
     * Build a human-readable retry context string from the latest checkpoint.
     * Returns null when no checkpoint exists.
     */
    buildRetryContext(taskId: string): Promise<string | null>;
    /**
     * Check if at least one checkpoint exists for the given task.
     * Returns false when no checkpoint file exists, the file is corrupt, or the array is empty.
     * Lighter than getLatestCheckpoint when only existence matters.
     */
    hasCheckpoint(taskId: string): Promise<boolean>;
    /** Get the absolute path to the checkpoints directory. */
    private getCheckpointsDir;
    /** Get the absolute path to a task's checkpoint file. */
    private getCheckpointPath;
    /**
     * Read all checkpoint entries for a task from disk.
     * Returns an empty array if the file does not exist or is corrupt.
     */
    private _readAll;
}
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