## Problem Given intervals sorted by start value, merge every pair of overlapping intervals and return the resulting non-overlapping intervals in ascending start order. Intervals that touch at one endpoint are considered overlapping. ### Function Contract Implement `merge_intervals(intervals) -> list[list[int]]`. The input must not be mutated. ### Constraints - `1 <= len(intervals) <= 200000`. - Each interval is `[start, end]` with `start <= end`. - Input intervals are already sorted by nondecreasing start. - Endpoints lie in `[-10^9, 10^9]`. ### Examples - `[[1,3],[2,6],[8,10],[15,18]]` returns `[[1,6],[8,10],[15,18]]`. - `[[1,10],[2,3]]` returns `[[1,10]]`; the inner interval must not shrink the result. ```hint Compare with the last merged interval When the next start is within the last merged range, extend its end with the maximum of both ends. ``` ### Edge Cases - One interval is returned unchanged. - Fully contained intervals do not change the merged end. - A chain of pairwise overlaps becomes one interval.