Renders a video composition baseline-vs-fast on a native amd64 Linux runner and
asserts the fast (drawElementImage) output matches via PSNR — validating the
BeginFrame paint path captures video, which couldn't be checked locally
(macOS has no BeginFrame; Docker-on-rosetta hung).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>