As part of a BCG X data-quality validation routine, you need to identify whether two sorted measurement values combine to a required target. Given a nondecreasing list of integers and a target integer, return the indices of two distinct elements whose values add up to the target.
Use the fact that the list is sorted to improve on a brute-force pair search. Indices are zero-based. Return the pair as [left_index, right_index] with the smaller index first. If no valid pair exists, return []. Each input contains at most one valid pair.
Implement find_pair_indices(nums, target), where nums is a sorted list of integers and target is an integer. The function returns a list containing two integers, or an empty list when no pair exists. The same element cannot be used twice.
def find_pair_indices(nums, target):