Software decode uploads swscale RGBA with no CSC/tonemap pass. On the new
desktop-compositor HDR10 surfaces (GNOME 48 / Plasma 6 + Mesa >= 25.1 offer
ST2084 even on SDR desktops) that sRGB-encoded content was composed as PQ —
the field-reported psychedelic picture (Fedora clients decode HEVC in
software because stock Mesa strips it; reproduced + fix live-validated on
GNOME Wayland: mode-0 soup -> HDR→SDR washed-out-but-correct).
The CPU lane keeps the SDR swapchain and its known untonemapped-PQ gap; a
real PQ→sRGB pass for CPU frames is the follow-up.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>