Package: ftp.debian.org libayatana-ido3-0.4-dev is no longer built by ayatana-ido, when I look at the cruft report to see why it isn't being cleaned up I see
* source package ayatana-ido version 0.4.4-1 no longer builds binary package(s): libayatana-ido3-0.4-dev on amd64,arm64,armel,armhf,hurd-i386,i386,kfreebsd-amd64,kfreebsd-i386,mips,mips64el,mipsel,ppc64el,s390x - suggested command: dak rm -m "[auto-cruft] NBS (no longer built by ayatana-ido)" -s unstable -a amd64,arm64,armel,armhf,hurd-i386,i386,kfreebsd-amd64,kfreebsd-i386,mips,mips64el,mipsel,ppc64el,s390x -p -R -b libayatana-ido3-0.4-dev - broken Build-Depends: cairo-dock-plug-ins: libayatana-ido3-0.4-dev mate-indicator-applet: libayatana-ido3-0.4-dev
When I look those two packages up on packages.debian.org I see that libayatana-ido3-0.4-dev is now a virtual package provided by libayatana-ido3-dev, so removing it will not actually break the build-dependencies. Can you remove libayatana-ido3-0.4-dev from unstable so that ayatana-ido can migrate to testing?