I feel like a lot of issues you mention will eventually point to an ambiguous spec. I’ve had great success with interview style spec generation where I ask agent to grill me on any and all parts of the spec/plan that’s ambiguous and then note my responses. It takes like 10 mins but the end product is always exactly what I expect and most of the things you mention get resolved in this interview phase.
replyAll informal specs are of course to some extent ambiguous. (I should mention that I have a background in formal methods and have also worked with formal specification tools.) And what you suggest is a process that I have used also, and it will cover some obvious gaps, but not all, at least for non-toy projects.
replyIf you want to go all the way, a fully formalized specification is not less work than writing the software, though the potential promise of LLMs for formal methods is interesting.
But for any informal specs, no matter how detailed, while LLMs can be very capable when it comes to avoiding surface errors when translating them into code (e.g. they're more likely than human programmers to write code that compiles on first try), they still don't have a mental model, and most of the problems I've seen are IMO results of that and they increase with the scale of the project.