Thanks for taking the time to document some of that!
I found that there is a lot of code that could be reused in other applications. For example your Q2MagmaMock or Q2Log could benefit other applications.
More details about the motivations behind the classes in the following categories could help reading the code, I think. The very high level intent is understandable but drilling in the details is hard. Q2-HV Q2-Magma-addons Q2-Scheduler Q2-Seaside-addons Q2-Sessions Q2-Transactions Q2-Utilities Q2-Translation
Another area of confusion for me, not directly related to Gjallar, is the versioning mechanism in Squeak. I had started creating some code in 3.9 (learning from the Pier/Seaside/Magma application example). But I found hard to understand what will and will not work under 3.9 and/or the latest Seaside/Magma versions. I guess that this comment belongs to another discussion list ;-)
Happy badminton! Thierry