komoot: get the places right, then put them in order

Implement a reorder-and-undo module for a route editor. After several changes to waypoint order, users should be able to undo those changes in reverse order.

1. Initial data: Initialize the module with ["S","W","V","E"], representing Station, Water stop, Viewpoint and Exit. The module owns its state and must not modify the supplied array. Every subsequent order is guaranteed to be a complete permutation of these four distinct IDs. This exercise allows the start and finish to be reordered too; input validation is out of scope.
2. Operations: Provide reorder(nextIds), undo() and snapshot(). Each returns a copy of the current order. reorder saves the previous order before adopting a new one; if the order is unchanged, it adds no undo record. undo restores and removes the most recent undo record; with no records, it leaves the order unchanged. Modifying any returned array must not change internal state.
3. Acceptance: Starting from the initial order, call reorder([S,V,W,E]), repeat the same call, then call reorder([S,W,E,V]). The results are [S,V,W,E], [S,V,W,E] and [S,W,E,V]. Three successive undo calls must return [S,V,W,E], [S,W,V,E] and [S,W,V,E]. Change the first item of one snapshot to X; another snapshot must still return [S,W,V,E].
4. Deliverable: Implement the module in a language you know, run the sequence above, and explain who owns the current order and history. Work only with local IDs: no map drawing, route calculation, redo or persistence across reloads.