If there's no way to regenerate book.html it should be removed and redirect to https://docs.freebsd.org/en/books/porters-handbook/
jrm@ also managed to find two more outdated versions https://download.freebsd.org/ftp/doc/en_US.ISO8859-1/books/porters-handbook/book.pdf https://download.freebsd.org/ftp/doc/en/books/porters-handbook/book.pdf There's a newer copy of it here in pdf format (jrm@ provided a link) https://people.freebsd.org/~ceri/porters-hb.pdf
We should clean that. There is a single/full version of the porters-handbook in this link: https://docs.freebsd.org/en/books/porters-handbook/book/ It's still not listed anywhere.
https://docs.freebsd.org/en/books/porters-handbook/book.html is now redirecting users to the new documentation. PDF is still an issue.
Mmmm, ok, but, where is the single page book.html now?
(In reply to Mathieu Arnold from comment #4) https://docs.freebsd.org/en/books/porters-handbook/book/
This is now fixed