Using a locked-down WordPress as the form backend for my static sites (opens in new tab)

Static sites are great: fast, cheap to host, almost nothing to attack. Then you add a contact form and hit the same wall everyone hits — a static site can't process a submission. You need a backend. The usual answers are a third-party service (Formspree, Netlify Forms, Basin) or a small server you now have to babysit. Both add a dependency you don't control, a recurring bill, and — the part that bugs me most — your submission data lives on someone else's infrastructure. There's a third option...