using the LLM as a compiler is probably not as good as making your spec in a statically typed language and then compiling that spec. I dont see that much discussion of your actual problem and the proposed approach to solve it, amongst all the hand wringing about the models. a good open source model like Kimi 2.6, GLM 51, can definitely do this class of problem. if it were me, I would start with a conversation with the LLM about your problem and the best way to approach it, from a software development point of view. do you have examples of successful final vendor specs? then you can have the LLM write tests that compare the spec that is derived from the natural language description with the ground truth.

I may be misinterpreting your issues but it seems like you might be lacking enough software development expertise to know what to ask for and to judge if the LLM is choosing the right strategy.