I hid zero-width characters in a CS1 spec. The model did not blink.
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I made two sabotaged copies of a CS1 problem. Into the first I inserted zero-width characters, invisible in any editor. Into the second I went heavier and swapped letters for Unicode look-alikes as well. The hidden tests stayed byte-for-byte identical. If obfuscation works as an AI defense, the model's score should drop. It scored 0.85 on both copies. The attack did nothing. My fairness check flagged both copies anyway, and that second part is the one worth writing about. Auditing AI-Solvability ยท Part 4 of 5 1 2 3 4 5 Why sabotage my own problem # Instructors keep looking for ways to make assignments that AI tools fail. One family of ideas is to leave the problem alone and poison the text: invisible characters, homoglyphs, formatting tricks that a human reader never notices but that might derail a model reading the same bytes. Before trusting any resistance my tool (part 1) reported, I needed to know what this kind of tampering does to a score, because a problem that scores low for wording reasons is fake difficulty, not a real skill gap.