/**
 *
 * Writes a JSON snapshot of the current session's state to
 * `_runtime/<sessionId>/checkpoints/<iso-timestamp>.json`. Idempotent —
 * any number of checkpoints may exist; the service prunes the oldest
 * beyond `MAX_CHECKPOINTS` so the directory does not grow without bound.
 *
 * Designed for skill-level invocation (NG1). The LLM is the only one
 * that knows when context pressure is high; the CLI is the muscle.
 */
export type CheckpointReason = 'context-fill' | 'periodic' | 'artifact-written' | 'user-pause' | 'user-close';
export declare const CHECKPOINT_REASONS: readonly CheckpointReason[];
export interface CheckpointSnapshot {
    sessionId: string;
    lastActivity: string;
    currentPlan: string;
    openQuestions: string[];
    recentDecisions: string[];
    recentArtifactPaths: string[];
    gitStatus: string;
    skillsActive: string[];
    todoState: string[];
    reason: CheckpointReason;
    createdAt: string;
}
export interface CheckpointOptions {
    sessionId: string;
    reason: CheckpointReason;
    /** Injectable clock for deterministic tests. Returns ISO timestamp. */
    now?: () => Date;
    currentPlan?: string;
    openQuestions?: string[];
    recentDecisions?: string[];
    recentArtifactPaths?: string[];
    gitStatus?: string;
    skillsActive?: string[];
    todoState?: string[];
}
export declare function isValidCheckpointReason(value: string): value is CheckpointReason;
export interface CheckpointWriteResult {
    path: string;
    sessionId: string;
    reason: CheckpointReason;
    createdAt: string;
    pruned: string[];
    totalRetained: number;
}
export declare function writeCheckpoint(projectRoot: string, options: CheckpointOptions): CheckpointWriteResult;
export declare function readCheckpoint(path: string): CheckpointSnapshot;
export declare function listCheckpointPaths(projectRoot: string, sessionId: string): string[];
export declare function latestCheckpointPath(projectRoot: string, sessionId: string): string | null;
export declare const CHECKPOINT_CONSTANTS: {
    readonly CHECKPOINTS_DIR: "checkpoints";
    readonly CHECKPOINT_FILENAME_EXT: ".json";
    readonly MAX_CHECKPOINTS: 10;
};