fix: make Guacamole fixture dual-stack and keep VM display awake

scripts/windows/test-host

@@ -316,6 +316,18 @@ wait_guest_additions() {
     fail "Guest Additions did not publish version and Windows OS-release properties"
 }
 
+configure_display_keepalive() {
+    # VirtualBox VRDE reports a zero-bpp framebuffer when Windows powers off
+    # the virtual monitor.  That leaves an authenticated Guacamole tunnel in
+    # its "Waiting for response" state even though RDP negotiation succeeded.
+    # Keep the disposable diagnostic fixture awake; this is deliberately
+    # applied after every snapshot restore because power-plan state belongs to
+    # the guest snapshot, not to the controller.
+    provisioner_run --exe 'C:\Windows\System32\cmd.exe' --wait-stdout --wait-stderr --unquoted-args -- \
+        /d /s /c '(powercfg /change monitor-timeout-ac 0 && powercfg /change monitor-timeout-dc 0 && powercfg /change standby-timeout-ac 0 && powercfg /change standby-timeout-dc 0 && powercfg /change hibernate-timeout-ac 0 && powercfg /change hibernate-timeout-dc 0 && echo RVBOX_GUEST_OK)' >/dev/null || \
+        fail "fixture provisioner could not disable disposable display/sleep timers"
+}
+
 wait_service() {
     wanted=$1
     attempt=0
@@ -366,6 +378,8 @@ case "$action" in
         step prepare-vm-started
         wait_guest_additions
         step prepare-guest-additions-ready
+        configure_display_keepalive
+        step prepare-display-keepalive
         assert_clean_guest
         step prepare-clean-baseline-verified
         ;;