/**
 * Device source evaluator.
 *
 * A fleet device becomes the watched source. Reuses the real load/health probe
 * (lib/devices/health.ts) — the first scheduler consumer of it — so a monitor can
 * fire "when a box goes loaded / unreachable". The observation is
 * `<reachable>\t<headroom>` plus the full DeviceStats in meta, so an on-change
 * monitor fires on a headroom-bucket flip and a match monitor can match `loaded`.
 */
import type { MonitorSource } from '../config.js';
import type { Observation } from './types.js';
/** Probe the device and return reachability + headroom bucket as the observation. */
export declare function evaluate(source: MonitorSource): Promise<Observation | null>;
