In-place upgrade to 4.2 from 4.1 ruins sound on supported templates by spurios switch to pipewire

[verygreen]

I updated Qubes Qubes 4.1.2 to Qubes 4.2 and afterwards all sound output in "supported" template qubes disappeared (meaning fedora 37/38 - the only ones I was actually using). Fedora36 template I had lying around was not affected.

Problem is seen as lack of "Port" subsection under Output devices in audio mixer/pavucontrol "Output devices" tab under "Qubes VCHAN Sink" where as with the pulseaudio present you'll have a

It looks like part of the upgrade process performs dnf swap pulseaudio-qubes pipewire-qubes which erases pulseaudio devices in supported templates (i.e. not Fedora36). as described in #7832
But it appears that dom0 pipewire is not prepared/installed.

As a test I cloned my fedora37 template, executed dnf swap --allowerasing pipewire-qubes pulseaudio-qubes and that restored sound output in ant vms based on this template (After restart of the template).

But now here's a weird kink, once I did that and did a sound output form pulseaudio-enabled qube, all of a sudden all other qubes that still had pipewire in them (based on unfixed tempates) started to output sound without any problems. So this seems to imply some bit of init only happens the first time actual pulseaudio client is run?

For comparison I have a clear install of Qubes 4.2 (I think it was rc2, then updted normally to RC4) and that sitll has pulseaudio in all its templates and sound has zero problems.

This is likely also similar to #8560, but I cannot be 100% sure so I am filing this ticket with additional findings I have