For stable-diffusion-cpp-python:
- GGML_VK_VISIBLE_DEVICES=
- GGML_VULKAN_DEVICE=

For llama-cpp-python (additional):
- VK_ICD_FILENAMES=/dev/null
- VK_DRIVER_FILES=/dev/null
- VK_LOADER_DRIVERS_DISABLE=*
- VK_LOADER_LAYERS_DISABLE=~all~

All variables are restored on cleanup for subsequent Vulkan models.