One click to permanently delete selected files — no Trash, no recovery. The button Apple never dared to add.
Installation
Download the DMG from the link above, open it, and drag OneDown.app to your /Applications folder.
Open OneDown — macOS will block it because it's not notarized. Go to System Settings → Privacy & Security, scroll down, and click "Open Anyway". Notarization requires an Apple Developer account — which costs $99/year.
The Delete Forever button appears in your Finder toolbar automatically. You can close OneDown — the button stays.