Puppet 7 changes certname to hostname, was fqdn

Puppet Version: 7.0.0, Facter 4.0.46
OS Name/Version: Debian 10

Puppet 6 used fqdn for certname. Puppet 7 uses hostname. This change isn't mentioned in the release notes:

• https://puppet.com/docs/puppet/7.0/release_notes_puppet.html
• https://puppet.com/docs/puppet/7.0/release_notes_facter.html

Documentation still says certname defaults to the fully qualified domain name: https://puppet.com/docs/puppet/7.0/config_important_settings.html

Desired Behavior:
Keep using fqdn for certname.

Actual Behavior:
Suddenly agents want to use their short hostname for the certname, which causes them to request new certificates.

This is despite facter still having the correct values:

kenyon@hydrogen ~ % facter hostname

hydrogen

kenyon@hydrogen ~ % facter fqdn

hydrogen.kenyonralph.com