Flaky issue when using gr.themes.builder()

[abidlabs]

I'm unable to run the theme builder locally. I get this error in the console:

Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'forEach')
at handle_update (Blocks.svelte:316:8)
at Blocks.svelte:451:7

This error happens consistently for me, but not for @freddyaboulton so it could be related to some race condition.

Repro

1. Run gr.themes.builder()
2. Try to change the base theme -- the UI freezes up

[hannahblair]

I can run the theme builder and change the base theme without it freezing up, but I do see the error you're seeing in the console

edit - theme changing actually works fine when running via the backend server but freezes up in the frontend server