/api/html/render-frame cannot produce a transparent frame

A page rendered with a transparent background comes back with an opaque white background instead of alpha.

Steps to reproduce
1. POST to /api/html/render-frame with html whose body has background: transparent
2. Inspect the returned PNG

Expected
A PNG with an alpha channel, transparent where the page is transparent.

Actual
A solid white background.

Context
This forces any decorative asset (logos, marks, overlays) to be composited as a full-frame video on its own fixed ground rather than as a transparent overlay, which means the ground colour has to be baked in and cannot change per use. Alpha output would remove that constraint entirely.

Environment
App version: 8.8.0
Platform: Windows 11 Pro 10.0.26200