I am not sure whether it is useful to re-use this bug for the new problem.
My interpretation here is that currently the installation on testing fails because it requires both postgresql-q3c *and* pgsphere extensions for postgresql, and in the moment only postgresql-q3c is updated to postgresql-18 in unstable, pgsphere still remains postgresql-17 (the updated version is still in NEW). This Franken-postgres will surely make an installation (or upgrade) break, and my prediction is that it will succeed magically once we have the updated pgsphere.
Cheers Ole
