[hybrid] Suspected corruption with gradients

[nicoburns]

This issue affects the rendering of servo.org with Blitz's vello_hybrid branch.

To reproduce:

• Clone and checkout https://github.com/nicoburns/blitz/tree/vello_hybrid
• Run cargo run -rp readme servo.org

Expected (rendered with vello_cpu)	Actual (rendered with vello_hybrid)

Additionally the rendering seems to change on re-renders (it's a static gradient, so it shouldn't):

Screen.Recording.2025-10-12.at.01.24.09.mp4