Always 501 today (open question G-4). The body is validated first, on purpose: a client
learns the feature is missing rather than that its payload was wrong.
Always, today. No annex defines evaluators, datasets, scoring or how a result relates to a run, so there is nothing to run — see open question G-4 in docs/OPEN-QUESTIONS.md. The tables and the two read endpoints exist; the write path is deliberately absent rather than improvised. Branch on the error code not_implemented; do not retry.
The body shows the fields the schema always carries. Which combination is legal is a service rule the schema cannot express, so read the description above before copying this.