Verified locally in debian:12 and fedora:43 containers before pushing:
- deb: dpkg-deb rejected the control file because `paste -sd', '` uses
the delimiter list cyclically (comma, space, comma, ...) — join with a
plain comma instead;
- rpm: rpm 4.20+ (Fedora 43) computes %{buildroot} itself and ignores a
caller-supplied buildroot define, so stage the payload and let the
spec's %install copy it via %{_oak_stage}; add a changelog entry (the
%source_date_epoch_from_changelog warning) and drop it from the
changelog-less build.