jsonschema.TypeChecker with additional types fails to work after several reference resolutions by the referencing.Registry about jsonschema

[Julian]

I suspect this is likely a duplicate of #994, albeit your example is a much more reasonable one (in terms of it being behavior that seems like it clearly should work). If it is a dupe, there's still no fix quite yet for the behavior, it may need to wait for a refresh of the dialect behavior overall, but there was a workaround or two mentioned there in the thread (which boil down to "if you want all Draft 7 to behave this way, then declare that your extended validator is the one that validates Draft 7 and fully override the built in one").

[Julian]

I've moved this example there -- though I think supporting this fully will likely not come until some larger work reworking how dialects are "registered" (or here re-registered) in jsonschema happens. You can watch that issue for updates, or feedback / suggestions are of course welcome.