The typed descriptor heaps write a null descriptor for a null guest
image, and the device therefore required VK_EXT_robustness2's
nullDescriptor. MoltenVK has the extension but not the feature, so on
macOS no Vulkan device opened and every GPU test was skipped. The
feature is now enabled when the device has it. Without it, the device
creates a placeholder image per typed image heap: 1x1, cleared to zero,
of the heap's dimension, sample count, numeric class and access, and a
null guest image binds the placeholder of its heap. A heap whose
placeholder the device cannot create throws when a null image reaches
it. TechnicalDebt.md lists where a placeholder differs from a null
descriptor.
agc_placeholder_images checks every image resource the recompiler maps
to a heap against that heap's placeholder, so the two cannot drift
apart, and agc_shader_device_profile now expects a device without
nullDescriptor to be accepted.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Arvind Frøiland