The only other way to do this is WebMention which is supported in yarnd – But @lyse@lyse.isobeef.org is spot on here too 👌

I agree. It’s more organic to make the connection by another channel. On using the web server logs, I think that isn’t easy to integrate, and it’s also prone to spam.
Webmentions sounds good to not reinvent the wheel.

Perhaps the Endpoint should be indicated inside the .txt instead of the HTML.

Anyway, I’ll take a look into adding Webmentions support in the PHP client soon.
https://indieweb.org/Webmention-faq