Following the documentation[1] starting at ve.ui.Surface (from ve.instances[0]) one would go to #getContext and access .toolbar. But though that property is defined, it is set to null.
I'm not sure why, but apparently our MediaWiki's init is instantiating its own and is only accessible from ve.init.mw.ViewPageTarget#toolbar (ve.init.mw.targets[0].toolbar).
It probably shouldn't have to instantiate its own one, and certainly not make it inaccessible to the rest of VE.
[1] https://doc.wikimedia.org/VisualEditor/master/#!/api/ve.ui.Surface
Version: unspecified
Severity: enhancement