Some drivers (e.g. Intel Vulkan on Linux/Windows) can't render to Rgba32Float,
so creating the 'fs_content' pipeline panicked with 'Format Rgba32Float is not
renderable' as soon as a document/image was opened. The accumulation format is
now chosen per adapter: Compositor::preferred_acc_format() keeps Rgba32Float
where it's a valid render target and falls back to Rgba16Float otherwise. The
compositor carries the format (pipelines, accumulation texture, byte size and
the readback half-decode all follow it); the app picks it from the eframe
adapter. Capable GPUs are unchanged (parity still exact, 18/18). A new test
forces the Rgba16Float path on any GPU and confirms it renders within display
tolerance (blend + adjustment). wasm green.
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
