The Linux runner has no GPU, so the GPU tests ran on Mesa llvmpipe over
GL, which can't render Rgba32Float: 57 GPU checks (50 GPU parity, 3
canvas, 2 adjustment preview parity, 2 effect-map recovery) returned
early and passed without comparing anything. A new step after Test
installs mesa-vulkan-drivers and runs the nextest `gpu` group on
lavapipe (Vulkan), reusing Test's build, and fails unless the parity
tests report the Vulkan backend and no test printed a skip.
No code change: photocraft's tests take whatever adapter wgpu returns,
software adapters included. Follows the CI half of lightcraft#1148.
Co-authored-by: FredApps <FredApps@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
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