solved long ago. https://github.com/jirutka/doas-sudo-shim/

so do I uninstall sudo from my distro? What do I do on upgrade? This shim is available from alpine package manager, can I get it anywhere else?

It's single, self-contained shell script. If it's not packaged for one's distro, amd they don't know how to replace a command and keep it updated, then this shim is not for them, and that is ok.

For the technically inclined who like challenges, creating a distro package of this shim is the "hello world" equivalent for packaging.