As it always is with these articles, that has nothing to do with non-determinism the author is talking about. Model's input is in natural language which isn't formally defined, unlike Ragel's input. This makes it open to interpretation by the model that isn't trained the same way as you, has very limited cognitive capabilities, and must generate something in very limited time by design, even if the result is incorrect. This also makes it not related to determinism in any way. You can make model outputs deterministic, but this won't solve your problem because it's not about determinism. Words have meaning.

Claude or any other model just translates your natural language instructions into formally defined tool calls. You cannot replace this layer with a formal tool like Ragel. You can write code for Ragel directly, in which case the responsibility for this is yours and not Claude's. (duh)

>What about Claude? Well, my instructions say in all caps: DO NOT PARSE ANYTHING MANUALLY, EVER. (...) It tries anyway

This needs a self-verification loop. It still won't guarantee that model's interpretation will match yours, but it will improve the accuracy. Almost every model will know that it went off the rails upon checking what it's trying to do. Harness has to provide the loopback for this, because the transformer architecture doesn't.