Please upgrade to 2.3 here.
The 2.2 and earlier branches are no longer being updated.
How does one change the embed-friendly theme so it works with Debug like all the other themes?
it's the only theme shipped with Vanilla which doesn't show debug info. Even the mobile will show debug info.
I may not provide the completed solution you might desire, but I do try to provide honest suggestions to help you solve your issue.