I spent quite a while trying to fix a non-issue: I couldn't find .well-known/site.standard.publication in my browser.

However, the reason it wasn't "existing" is that it's being served as a generic download rather than a text file. When my browser tried to open it, the request was "aborted" because the browser didn't know how to render the .publication extension and simply tried to download it.

fix:

public/_headers#

/.well-known/site.standard.publication Content-Type: text/plain

And yes https://site-validator.fly.dev/ can deal with this, but it is a low cost enhancement?