I’ll try to explain my thoughts after discovering the issue that mentioned that testing systems enable the buster-backports. I thought:
Having that backports line pointing to buster in testing currently makes the backports to stable buster work, without disturbing testing, thanks to older or equal versions and same priorities (the fixed bug above).
After the release buster-backports may still be technically there, but I think it won’t work for the new-stable (bullseye) to have a backports line that points to old-stable buster-backports (thus breaking with release).
And I thought, whatever mechanism fixes this should also be able to adjust freedombox testing systems to follow stable instead of staying on the testing branch, or the current release (bullseye) forever.
Now to your answer.
First, thanks for pointing out that the backports repository also gets frozen, it’s a good point that I didn’t account for in the approach for package triggered updates. So package driven updates might only be possible with https://fasttrack.debian.net/
But from your links, I see there already is a mechanism and it works differently.
I gather that the system’s sources list is expected to be configured to point to “stable” or “testing”. The system checks the codenames of the available stable and optionally testing repositories, and updates to any new codename if one becomes available. Correct?
- I’m wondering if the current implementation allows to upgrade an installed system for a second time. (Because after the sources list has been changed from the generic “stable” or “testing” used in the images, to codename based entries, there is no “stable” or “testing” in the list that can be found and replaced for the next release upgrade.)
- I think fixing 1. should also make it trivial to support building the testing images with fixed codenames in the sources list. So that testing installs can default to become “stable”, simply by using the codename in the images while they are still part of the testing branch, and then only completing the sources list (backports?) when released as stable. (Afterwards such systems may optionally still get updated to the next testing again, if the system runs with test_upgrade=True.) All the while the fix for 1. also allows these former testing systems (with a codename in sources list) to get later upgraded to the following stable releases.