Thanks to Tobias for his several bug reports. I committed fixes to the issues, building my own ensure-package (in a labels in cl-user, because we don't have a package in which to do a defun yet).
RPG:
Follow-up question: why do we need the ASDF-EXTENSIONS nickname? Can we sacrifice this instead of giving up DEFPACKAGE? Is it for backwards compatibility with some specific, small number of symbols that used to be in ASDF-EXTENSIONS?
It is for backwards compatibility indeed.
[ François-René ÐVB Rideau | Reflection&Cybernethics | http://fare.tunes.org ] It is useless to attempt to reason a man out of a thing he was never reasoned into. — Jonathan Swift