/** Pure display-formatting helpers, reachable by `bun test` without a DOM (design.md D23). */
/** Formats an elapsed duration as a compact age string: "8s", "2m", "1h", "3d". */
export declare function formatAge(elapsedMs: number): string;
/** Whether a polled observation is older than its own refresh interval — presented as stale rather than current (design.md "Stale data is labelled"). */
export declare function isObservationStale(observedAt: number, refreshIntervalMs: number | undefined, now: number): boolean;
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