17:19:21 # Life updating old chroot in sbuild that predates usrmerge. I have been lazy and haven't been updating the chroot; but I no longer could, so had to resolve this issue about usrmerge. There was a file /etc/unsupported-skip-usrmerge-conversion that usrmerge package errored out on; it seemed like it means a mark of not doing usrmerge conversion, because sbuild is a system for autobuilding and staying in split /usr for the duration of the release might be better. I don't fully understand the rationale of the file and effects, but I just deleted it and jumped into merged usr.
# sudo sbuild-shell debcargo-unstable-amd64-sbuild # rm /etc/unsupported-skip-usrmerge-conversion # dpkg --configure usrmerge