Masks are applied before effects, but the noise was composited with the
Opacity alpha alone, so a masked solid filled the whole layer. The result
is now multiplied by the original alpha on the CPU and on both GPU paths
(kernels.wgsl for the default settings, fx_noise.wgsl for the rest).
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>