Did you get the TypeFox Theia Workshop project to work? The JSON-Form Widget is exactly what I’d need for my own project, but unfortunately the sources are outdated and no longer work with the latest version of Theia.
The schema registration and the indexedDB errors are most likely unrelated. If you want to fix the indexedDB error, try to avoid running the app in an incognito mode/tab, or make sure you’re Firefox (if you are using that) can remember history.
In the workshop example, when I open the custom editor and make a change so that the model state gets dirty, the respective JSON file gets opened in Monaco editor as well. Only the Monaco editor tab shows the little dot indicating a dirty state and allows saving of the changes.
I would like my users to work in the custom editor only, though, so I am wondering what I have to do so the custom editor can be self-contained. Presumably, I need to implement SaveableSource? What about Navigatable or StatefulWidget, as EditorWidget does? Or should I rather just extend EditorWidget instead of BaseWidget?