Leetcode 2737. Find the Closest Marked Node

Given an undirected tree (or graph) where nodes can be toggled "marked," support operations that mark/unmark nodes and queries that ask for the shortest distance from a given node to the nearest marked node. The challenge is to answer many dynamic distance queries efficiently (better than recomputing BFS from scratch), typically requiring multi-source shortest-path ideas or tree decomposition/centroid techniques.