This feels related to T242545 and probably takes me enough time to welcome a dedicated task.
- https://www.mediawiki.org/wiki/Gadget_kitchen (Side note: Does everyone get the "kitchen" metaphor? I doubt.)
- https://www.mediawiki.org/wiki/Gadget_kitchen/Training (these are rough notes from 2012 with sentences like "Ask Roan outside this room about the future of gadgets, which will make certain things easier.")
- https://www.mediawiki.org/wiki/Gadget_Studio (a stub page from 2011)
Also note that https://commons.wikimedia.org/wiki/File:Userscript_and_Gadgets_workshop_toolkit.pdf is a good tutorial resource by @srishakatux but currently not linked anywhere.