Install QEMU's virtio-vga display and check for it

The smoketest VMs start with -vga virtio, but Arch packages that display
apart from qemu-base, so the base image build failed with "Virtio VGA not
available". update.sh now installs qemu-hw-display-virtio-vga, and doctor
and smoketest run check QEMU has the display before anything downloads.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/common.sh

@@ -62,6 +62,12 @@ in_flatpak() {
   [ -f /.flatpak-info ] || [ -n "${FLATPAK_ID:-}" ]
 }
 
+# Whether QEMU has the display the smoketest's VMs start with (-vga virtio).
+# Arch packages it apart from qemu-base, as qemu-hw-display-virtio-vga.
+qemu_has_virtio_vga() {
+  [[ "$(qemu-system-x86_64 -device help 2> /dev/null)" == *'name "virtio-vga"'* ]]
+}
+
 # This project's folder
 sibling_dir() {
   cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd

lib/doctor.sh

@@ -50,6 +50,15 @@ cmd_doctor() {
     problem "not installed: ${missing[*]}" "fix: bash $(sibling_dir)/update.sh"
   fi
 
+  if command -v qemu-system-x86_64 &> /dev/null; then
+    if qemu_has_virtio_vga; then
+      ok "QEMU has the virtio-vga display the smoketest's VMs use"
+    else
+      problem "QEMU has no virtio-vga display, so the smoketest's VMs won't start" \
+        "fix: bash $(sibling_dir)/update.sh"
+    fi
+  fi
+
   if [ -r /dev/kvm ] && [ -w /dev/kvm ]; then
     ok "KVM is available for the smoketest's virtual machines"
   else

lib/smoketest.sh

@@ -56,6 +56,8 @@ require_vm_tools() {
     command -v "$tool" &> /dev/null \
       || die "$tool isn't installed. Install coredesktop-dev's packages: bash $(sibling_dir)/update.sh"
   done
+  qemu_has_virtio_vga \
+    || die "QEMU has no virtio-vga display. Install coredesktop-dev's packages: bash $(sibling_dir)/update.sh"
   [ -r "$KVM_DEVICE" ] && [ -w "$KVM_DEVICE" ] \
     || die "Can't use $KVM_DEVICE. Turn on virtualization (VT-x/AMD-V) in the firmware settings."
 }