If we go that route, can we have rich syntax highlighting, "go to definition"/"show usage sites", debuggers etc for the markdown docs as well? :)
But I don't really like the "LLMs as compiler" metaphor. If you followed that logic to the end, you'd have to "rebuild" your entire project from the spec every time the spec changes. Not just would the token cost be insane, but you'd also get a completely different implementation each time, maybe with different UI and design decisions where the spec left things open.
The alternative is to see the code as the source of truth and LLMs as (extremely sophisticated) editing or refactoring tools. Then by all means, still check in your prompts, but now they are documentation on how a feature was implemented, not the source of truth themselves.