The error is
09:25:57 I: Building the build environment 09:25:57 I: running debootstrap 09:25:57 /usr/sbin/debootstrap 09:25:57 E: /srv/pbuilder/aptcache/butster-amd64: No such directory 09:25:57 E: debootstrap failed 09:25:57 E: debootstrap.log not present 09:25:57 W: Aborting with an error 09:25:57 E: pbuilder create failed
I tested for a command injection but thankfully we run debian-parsechangelog before we inject what we extract from the distro-line to feed to pbuilder.
The error message, as you can see, is quite confusing. I think we should check whatever distro we find in dch against a list of known distributions and send a clear error otherwise.