Problem adding systemd-resolved to FAI generated image

[Rachel Roch]

What's the secret to adding systemd-resolved to a FAI image ?

I'm using fai-diskimage to build a Debian 12 (bookworm) image, its all working perfectly well, including systemd-networkd in conjunction with cloud-init to configure the interface when the image is booted.

However, having tested my image, I've discovered i need to add systemd-resolved so that the cloud-init DNS works correctly.

Now, you would think that is easy :
1. Add systemd-resolved to package_config
2. Add "$ROOTCMD systemctl enable systemd-resolved" to scripts

However, the instant I make those two changes, my build breaks.

I get all sorts of weird errors during the FAI build that I never got previously and are clearly linked to DNS resolution (and therefore systemd-resolved installation). For example :

===Err:5 https://deb.debian.org/debian-security bookworm-security InRelease                                                                       
Temporary failure resolving 'deb.debian.org'      
===

Reverting to my previous config space (i.e. removing from package_config and removing the scripts addition) the build process works perfectly again.  So without a doubt, it is systemd-resolved that is breaking the FAI build.
So what's the secret ?  How do I get systemd-resolved onto my image without breaking the image build process in the meantime ?