Sorry I didn't mean to. I was curious and asked some questions because both projects looks very very close to each other.
I just tested the offline support of CodeSandbox and I did manage to work with the editor (the same functionality you've mentioned in the blog post) when the network is offline. You can't test it here: https://codesandbox.io/s/new
Again, what you did is absolutely perfect and I don't want or mean to underestimate your work! :)