In the course of our discussions and code review for T238544: MEP Client MediaWiki JS (MVP) and T235189: Develop small client-side error logger for MediaWiki , we've identified a number of questions about architecture and the availability of certain methods in the client environment. These need to be resolved, possibly with patches but maybe through decisions we can make simply by discussing the matter more closely.
This task collects that work, which we would loosely hope to be completed before the end of FY 2019-20, although there is no firm triage right now.