/**
 * src/agent/heartbeat.ts
 *
 * Pillar A — Heartbeat + session resume.
 *
 * Exports `startHeartbeat(intervalMs)` which returns a session ID and a
 * JSONL writer that appends heartbeat records to
 * `.harness/traces/heartbeat.jsonl`. Each record carries:
 *   session_id, started_at, last_heartbeat_at, status
 *
 * Status transitions: running → idle → done | failed
 */
export type SessionStatus = "running" | "idle" | "failed" | "done";
export interface HeartbeatRecord {
    session_id: string;
    started_at: string;
    last_heartbeat_at: string;
    status: SessionStatus;
}
/** Returns the path to the heartbeat log, resolved from repo root. */
export declare function heartbeatPath(repoRoot: string): string;
/**
 * Start a heartbeat ticker.
 *
 * @param intervalMs  — milliseconds between heartbeat writes (default 30_000)
 * @param repoRoot    — repository root (default process.cwd())
 * @returns {{ sessionId: string, stop: () => void }}
 */
export declare function startHeartbeat(intervalMs?: number, repoRoot?: string): {
    sessionId: string;
    stop: () => void;
};
/**
 * Mark a session as failed in the heartbeat log.
 * Reads the original started_at from the JSONL file if available.
 */
export declare function failHeartbeat(sessionId: string, repoRoot?: string): void;
/**
 * Mark a session as done.
 * Reads the original started_at from the JSONL file if available.
 */
export declare function stopHeartbeat(sessionId: string, repoRoot?: string): void;
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