A telemetry gateway accepts tokens made of exactly n digits. A monitoring run must contain every possible token as a contiguous window at least once. Return any shortest digit stream that achieves this. Digits may be 0 through k - 1.

The stream may begin and end with any digits. If multiple shortest streams exist, return any one. The checker validates length and coverage, not a particular traversal.

The useful model is a directed graph: each (n - 1)-digit string is a vertex, and appending one digit is a directed edge. A route that uses every edge once gives the required stream. Construct such a route without storing all expanded windows.