W3 of the oak task list. SurfaceBridge wraps an engine wgpu (Metal) texture
into an IOSurface-backed CVPixelBuffer for gpui's Surface element: a reused
pixel buffer created with kCVPixelBufferIOSurfacePropertiesKey +
MetalCompatibility, aliased to a Metal texture via gpui_media's
CVMetalTextureCache, with a GPU-to-GPU MTLBlitCommandEncoder copy (a
device.poll(Wait) before the blit keeps the v1 path correct and
synchronous). A CPU readback fallback (stage_readback/finish_readback)
works on any backend. The surface_bridge demo (demo feature) streams a
moving test pattern through the bridge into a window and prints FPS;
smoke-verified on macOS at 1280x720. Windows/Linux paths are left for a
follow-up (noted in docs/zh). 2 tests pass.
Mike-Solar
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