/**
 * Split a UTC interval into sub-intervals of `amount × unit`.
 *
 * - Returns an array of `{ start, end }` records that tile the interval.
 * - The final sub-interval is trimmed so its `end` never exceeds the original `end`.
 * - Returns `[{ start, end }]` when `start === end` (zero-length interval).
 * - Returns `[]` on invalid input (unparseable start/end, unsupported unit, non-positive amount,
 *   leap-second strings).
 *
 * @param start ISO UTC datetime string for the interval start
 * @param end ISO UTC datetime string for the interval end
 * @param unit duration unit string — any `DateTimeDurationUnit`
 * @param amount positive number of units per step
 * @returns array of `{ start, end }` records, or [] on invalid input
 *
 * @example splitIntervalByUnitUtc("2024-01-01T00:00:00Z", "2024-01-02T00:00:00Z", "hour", 6) // [{ start: "2024-01-01T00:00:00Z", end: "2024-01-01T06:00:00Z" }, { start: "2024-01-01T06:00:00Z", end: "2024-01-01T12:00:00Z" }, { start: "2024-01-01T12:00:00Z", end: "2024-01-01T18:00:00Z" }, { start: "2024-01-01T18:00:00Z", end: "2024-01-02T00:00:00Z" }]
 * @example splitIntervalByUnitUtc("2024-01-01T00:00:00Z", "2024-01-01T01:30:00Z", "hour", 1) // [{ start: "2024-01-01T00:00:00Z", end: "2024-01-01T01:00:00Z" }, { start: "2024-01-01T01:00:00Z", end: "2024-01-01T01:30:00Z" }]
 * @example splitIntervalByUnitUtc("2024-01-01T00:00:00Z", "2024-01-01T00:00:00Z", "hour", 1) // [{ start: "2024-01-01T00:00:00Z", end: "2024-01-01T00:00:00Z" }]
 * @example splitIntervalByUnitUtc("2024-01-01T00:00:00Z", "2024-01-02T00:00:00Z", "hour", 0) // []
 * @example splitIntervalByUnitUtc("invalid", "2024-01-02T00:00:00Z", "hour", 1) // []
 */
export declare function splitIntervalByUnitUtc(start: string, end: string, unit: string, amount: number): Array<{
    start: string;
    end: string;
}>;