vulkan present on Xwayland with proprietary nvidia modeset=0

[serenissi]

I observe that on intel + nvidia system booted with nvidia_drm.modeset=0 
(intel is primary), vulkan apps such as vkcube running on nvidia gpu 
present over Xwayland on xcb wsi. In this setup however swapchain fails 
on wayland wsi. This is also indicated by 
`vkGetPhysicalDeviceSurfaceSupportKHR` and vulkaninfo:

present support:
                        VK_KHR_xcb_surface     = true
                        VK_KHR_xlib_surface    = true
                        VK_KHR_wayland_surface = false

In the case of Xwayland, bufinfo shows dmabufs created by 'drm' and 
attached to the intel gpu so I think intel is importing the bo.

So I'm curious why without nvidia_drm.modeset enabled vulkan apps can 
presnt over Xwayland but fails to do so directly over the same wayland 
compositor Xwayland is running on.

Is it something intentional by the nvidia proprietary vulkan driver or 
there exists some technical reason behind it?

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