Costume stops updating stage after being cleared (not yet on prod)

[fsih]

This is on https://llk.github.io/scratch-gui/develop/ but not yet on prod.

From @carljbowman (abridged)
4 Go into the paint editor
6 Delete the cat and draw anything with the brush tool
The cat should delete and the new drawing should [appear on stage]
Instead, nothing appears

[fsih]

@BryceLTaylor @benjiwheeler this is probably a blocker!

[fsih]

We're patching at 2am! It's all very exciting

[adroitwhiz]

[fsih]

argh that gif is terrifying 😅