[GPU Canvas] `endFrame() before returning` regression when drawing child artboards with `draw()` ...

Description

After the Rive update that deprecated `drawCanvas` in favor of putting canvas logic inside `draw(self, renderer)`, rendering a child artboard that contains custom Lua node script causes an error: `endFrame() before returning`，and the child artboard fails to render.

See attachment: When setting the visibility of the child artboard's ParticleScript to false, the parent artboard renders normally. However, enabling its visibility breaks the rendering

Question

Is this a bug/regression from the `drawCanvas` deprecation, or is nested script drawing intentionally disallowed now?

If this is intended behavior and not a bug: What is the recommended way to apply a full-artboard GPU shader (like Pixelate) to a child artboard that relies on dynamic Lua code for its visuals?

#### Environment

BETA 0.8.5674