Requirements handed down - never seen it in 25 years. The requirements are always fluid, by definition. At best, you get a wish list which needs to be ammended with reality. If you have completely static requirements, you don't need an engineer! You just do it. Engineering IS refining the requirements according to empirical data.

Once you have requirements that are correct (for all well-defined definitions of "correct"), the code implementation is so trival that an LLM can do it :-)