It appears you have a reply widget loading at the same time as VE (in source mode, aka 2017 wikitext editor). Loading VE and the reply tool on the same page is not going to play nicely as there are still globals that are shared between the article VE surface, and the reply widget VE surface.

It would be nice to clean this up, but using VE and the reply tool in the same page session is hopefully quite rare.

The QuotaExceededError could be because localStorage is full, or because you are in a private tab?

Thanks for recording the video, that's always very helpful. I uploaded a copy of it here for posterity.

I'm surprised that it's possible to launch both the reply tool and the full-page editor at the same time, that seems bad. I found task T328041, which reports another problem with it. VisualEditor and DiscussionTools should probably share some global "lock" to prevent that from happening.

If there was an option to quit in the visual/wikitext editor, this would probably have been a lot less confusing (T85470: Users are requesting a "Cancel and exit without saving" option).

I'm surprised that it's possible to launch both the reply tool and the full-page editor at the same time, that seems bad.

I think localStorage autosave in DiscussionTools makes this a little bit more likely to occur.

Having DT treat "wgAction == edit" as a barrier to initializing a widget is probably reasonable, so long as all our in-session editor-load / page-content-refresh actions are suitably updating it. Would potentially need to work around section=new links for the new topic tool though.