Bug#1108193: apt: Ordering issue with libc6:i386 on amd64-m-a system breaks partial upgrade ("just apt and dpkg") from bookworm to trixie

On Sun, Jun 22, 2025 at 11:05:03PM +0200, Helmut Grohne wrote:
> mmdebstrap --variant=apt --architectures=amd64,i386 --include=systemd-timesyncd,libc6-dbg:i386 --chrooted-customize-hook='sed -i -e s/bookworm/trixie/ /etc/apt/sources.list && apt update && apt-get -y install apt' bookworm /dev/null

Further observations.
 * We may install libc6 instead of apt.
 * We may include systemd-container instead of systemd-timesyncd.
 * If we include systemd-resolved or systemd-boot instead of 
   systemd-timesyncd, the problem does not reproduce.
 * trixie's libc6 Breaks: system (<< trixie).
 * trixie's systemd Pre-Depends: libsystemd-shared (= ...)
 * trixie's libsystemd-shared Depends: libc6 (>= trixie)
 * All of systemd-container, systemd-resolved, systemd-boot and 
 * systemd-timesyncd Conflicts: systemd (<< trixie).
 * In the apt log you may see that apt unpacks libsystemd-shared and 
   only then considers deconfiguring systemd (which Depends: 
   libsystemd-shared (= ...)). Why is that legal?

Helmut