bug#36443: suspicion

[Robert Vollmert]

My suspicion right now is that there’s not any real mixup
happening, but that guix-daemon runs the build in a
different environment in the directory

/tmp/derivation-name.drv-0

which gets copied to

/tmp/derivation-name.drv-5

in the root filesystem by `guix build -K`, if directories
-0, -1, …, -4 already exist. In which case I’d suggest doing
something to the messages and/or documentation to make this
clearer.

E.g. instead of saying “keeping build directory <dir>” say
“keeping a copy of the build directory at <dir>”.