satproto's implementation involves complex cryptographic signing and that makes it very not static. One needs to run a program of some sort to use satproto. The only static part is that the json that's operated upon.

This is not true of indieweb's web mention: https://indieweb.org/Webmention

It just uses HTTP POST (like pingback/trackback/etc, except it has a second step verifying the page sending the webmention actually has a link to a URL on the website). You can them them with a browser or cURL or some complex backend script. Receiving them is as easy as logging POSTs to a specific URL endpoint or even using someone else's community backend your site interfaces with via javascript (ie, https://webmention.io/ - not static since it uses JS). Or anything in between.

Totally decentralized and very simple. I implemented a simple nginx POST logging format in the config to receive on my static site. And HTML forms on my static site can send. http://superkuh.com/blog/2019-12-11-3.html