/** Compute up to 3 evenly-spaced contour values up to threshold (deduped, min 1). */
export function isochroneContours(threshold: number): number[] {
  const raw = [
    Math.max(1, Math.round(threshold / 3)),
    Math.max(2, Math.round((threshold * 2) / 3)),
    threshold,
  ];
  return [...new Set(raw)];
}