import type { Pool } from 'pg';
export interface PoolMonitorOptions {
    pool: Pool;
    /** Emit a heartbeat this often. */
    intervalMs: number;
    /** Pool size, for saturation reporting. */
    max: number;
}
/**
 * Periodic health heartbeat for the Postgres pool.
 *
 * The failure this exists for is silent by construction: an exhausted pool
 * produces no error, no CPU, and no log line — requests simply queue in
 * `pool.connect()` forever. `waiting > 0` alongside `idle === 0` is that state,
 * visible in a single line, and the heartbeat continuing to print at all is
 * proof the event loop is still turning.
 */
export declare function startPoolMonitor({ pool, intervalMs, max }: PoolMonitorOptions): {
    stop: () => void;
};