`Gpu::new` refuses software adapters (llvmpipe / lavapipe, WARP): the CPU
pipeline is faster. CI runners have nothing else, so the CPU <-> GPU
equivalence tests have always skipped there.
`LIGHTCRAFT_GPU_ALLOW_SOFTWARE=1` admits them. The app never sets it and
the default is unchanged. On lavapipe all 134 compared renders stay within
max 1 LSB, mean <= 0.0003 LSB, the same as Metal on an M4 Pro.
The two big-source window tests used a 24 MP (288 MB) source. That is over
lavapipe's 128 MiB storage binding (the WebGPU default), so geometry ran on
the CPU and nothing was uploaded: one test failed and the other passed
without checking anything. They now use 3200 x 3200 (117 MiB): above
RETAIN_SOURCE_BYTES, so the source is still shared, and uploaded on every
adapter.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
