docs: run.sh --amd (venus on the AMD iGPU); gaming mode can't render in the VM, all tried

.claude/skills/cachyos-vm-testing/SKILL.md

@@ -187,6 +187,20 @@ gamescope, so set it back to plasma before the next reboot (below).
 
 ## Gamescope does not render in this VM
 
+
+Everything was tried (2026-09-25); don't spend time on it again:
+- virgl (default): no Vulkan, black.
+- `--vulkan --amd` (venus on the host 780M, RADV): gamescope and Steam run,
+  but virtio-gpu rejects every framebuffer gamescope makes ("Cannot import FB
+  to DRM ... not supported for scan-out", AR24 and XR24, also with
+  `--force-composition --disable-layers`): black. KWin crashes on venus
+  ("Illegal command buffer"), so Plasma freezes too.
+- nested gamescope with lavapipe (`vulkan-swrast`): refuses to start, lavapipe
+  lacks VK_KHR_present_id/present_wait.
+- Other hypervisors (VirtualBox, VMware) have no Vulkan at all.
+Check gaming mode (Steam's settings, HDMI-CEC section, refresh rates) on the
+real Steam Machine. The VM covers everything else.
+
 (Also after any re-apply that includes the conversion.)
 
 No suitable Vulkan (venus is unstable with the host NVIDIA driver). After

run.sh

@@ -1,9 +1,10 @@
 #!/bin/bash
 # CachyOS test VM for steamify.sh.
-#   [REPO=/path/to/cachyos-gamescope-boot] ./run.sh [install] [--nvidia] [--vulkan] [--fremont]
+#   [REPO=/path/to/cachyos-gamescope-boot] ./run.sh [install] [--nvidia] [--vulkan] [--amd] [--fremont]
 #     install    boot the installer ISO
 #     --nvidia   render the guest's virtio-gpu (virgl) on the host NVIDIA dGPU
 #     --vulkan   expose Vulkan to the guest (venus; needed by gamescope, can be unstable)
+#     --amd      with --vulkan: venus on the host AMD iGPU (RADV) instead of NVIDIA
 #     --fremont  report the Valve Steam Machine's DMI data (for testing the wizard)
 # REPO defaults to $HOME/projects/cachyos-gamescope-boot.
 # BIOS_VERSION=F7F0107 makes the guest report that BIOS version (DMI), e.g.
@@ -26,6 +27,7 @@ for arg in "$@"; do
         --nvidia) export __NV_PRIME_RENDER_OFFLOAD=1 __GLX_VENDOR_LIBRARY_NAME=nvidia \
                          __EGL_VENDOR_LIBRARY_FILENAMES=/usr/share/glvnd/egl_vendor.d/10_nvidia.json ;;
         --vulkan) gpu+=,hostmem=4G,blob=true,venus=true ;;
+        --amd) export VK_DRIVER_FILES=/usr/share/vulkan/icd.d/radeon_icd.json ;;
         --fremont) smbios+=(-smbios type=1,manufacturer=Valve,product=Fremont -smbios type=2,manufacturer=Valve,product=Fremont) ;;
         *) echo "unknown argument: $arg" >&2; exit 1 ;;
     esac