New workspace crate isolating the unsafe GPU<->encoder interop for
zero-copy hardware video encoding. Every link is validated by a test on
real Intel/Mesa/iHD hardware:
- nv12: GPU RGBA->NV12 compute (BT.709 full-range), byte-exact vs a CPU
reference.
- vaapi: VAAPI hwcontext + h264_vaapi encode (CPU-fed NV12 -> valid H.264),
and DRM-PRIME surface layout probing.
- vk_device: a custom wgpu Vulkan device that adds
VK_EXT_image_drm_format_modifier (+ external-memory fd/dma-buf) via the
wgpu-hal device-from-raw path, so a tiled VAAPI surface can be imported.
- dmabuf: import a VAAPI NV12 surface's tiled DMA-BUF as two aliasing wgpu
textures (Y=R8, UV=RG8) at the plane offsets.
- zerocopy test: render values via Vulkan straight into the VAAPI surface
and read them back 100% correct -- proving the GPU writes into the
encoder surface with no CPU copy.
Not yet wired into the editor; real-frame render + encode-from-surface +
fallback wiring follow. Linux-only (libva); other platforms fall back.
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