/**
 * Collapse a list of UTC intervals into the minimum set of non-overlapping intervals.
 *
 * - List-form generalization of `intervalUnionUtc`, which is pairwise only.
 * - Intervals are merged when they overlap or share an instant exactly (adjacent intervals
 *   ARE merged).
 * - Order of the input list does not matter; the result is sorted by start.
 * - Returns `[]` for an empty list.
 * - Returns `[]` when `intervals` is not an array, when any element is not a
 *   `{ start, end }` record of valid ISO UTC datetime strings, or when any element has
 *   `start > end` or a leap-second string.
 *
 * @param intervals array of `{ start, end }` records
 * @returns the minimum set of non-overlapping `{ start, end }` records, sorted by start, or `[]` on invalid input
 *
 * @example mergeIntervalsUtc([{ start: "2024-01-01T00:00:00Z", end: "2024-01-10T00:00:00Z" }, { start: "2024-01-05T00:00:00Z", end: "2024-01-15T00:00:00Z" }]) // [{ start: "2024-01-01T00:00:00Z", end: "2024-01-15T00:00:00Z" }]
 * @example mergeIntervalsUtc([]) // []
 */
export declare function mergeIntervalsUtc(intervals: Array<{
    start: string;
    end: string;
}>): Array<{
    start: string;
    end: string;
}>;