You are given an undirected graph with `n` nodes, a list of weighted edges, a start node, an end node, and a safety threshold. Each edge has a safety cost. Return the minimum possible value of the maximum edge cost used on any valid path from start to end, where every edge on the path must have cost less than or equal to the threshold. If no valid path exists, return `-1`. Function signature: ```python def minimum_required_safety(n: int, edges: list[tuple[int, int, int]], start: int, end: int, threshold: int) -> int: pass ``` Constraints: - `0 <= start, end < n`. - Edge costs may repeat. - The graph may be disconnected. - A path may contain one or more edges; if `start == end`, return `0`. - Only edges with cost less than or equal to `threshold` may be used. Examples: ```text n = 4, edges = [(0, 1, 5), (1, 3, 4), (0, 2, 2), (2, 3, 8)], start = 0, end = 3, threshold = 6 Output: 5 Explanation: 0 -> 1 -> 3 is valid and its maximum edge cost is 5. ``` ```text n = 3, edges = [(0, 1, 7), (1, 2, 3)], start = 0, end = 2, threshold = 5 Output: -1 ```