How we build the thing that publishes your changelog, your blog and your release notes.
If your sitemap address returns the post-not-found page, no route exists for it and the sibling dynamic segment is matching the whole thing as a slug. The repair is a real route at that exact path, because a static segment outranks a dynamic one.
The submit call is a PUT that returns an empty body. Whether Google fetched the file, whether it parsed and how many URLs it holds all come back from a different call, on Google's schedule rather than yours.
Market4 turns one release note into a changelog page, a blog post, a mail-out and a week of social posts — and then tells you which of them brought anyone back.