Add a --vnc option to run-windows11.py

Serves the guest screen over VNC instead of opening a display window.

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

run-windows11.py

@@ -84,11 +84,12 @@ download_only = False
 seed_only = False
 extra_args = []
 arch_option = None
+vnc_listen = None
 
 
 def usage(stream=sys.stdout):
     stream.write(f"""\
-Usage: {Path(sys.argv[0]).name} [--daemon] [--download-only] [--seed-only] [--install-from-iso | --install-from-img]
+Usage: {Path(sys.argv[0]).name} [--daemon] [--download-only] [--seed-only] [--vnc[=ADDR:N]] [--install-from-iso | --install-from-img]
        [--arch ARCH] [--state-dir DIR] [--rdp-port PORT] [--ssh-port PORT] [-- QEMU_ARGUMENT ...]
 
 If the system disk (DIR/disk.qcow2, see --state-dir) is missing, create it from
@@ -115,6 +116,9 @@ Options:
                       is the ISO path ending in .img instead of .iso.
                       It is attached as an NVMe disk, much faster than the
                       emulated USB CD-ROM, and is never modified
+  --vnc[=ADDR:N]      Serve the screen over VNC instead of opening a window, on
+                      ADDR (default: 127.0.0.1) at TCP port 5900+N (default N: 0).
+                      Overrides WIN11_VM_DISPLAY
   --arch ARCH         Guest architecture: arm64 or amd64 (default: the host's;
                       overrides VM_IMAGE_ARCH). A guest that differs from the
                       host runs under slow TCG emulation
@@ -155,6 +159,10 @@ while args:
         download_only = True
     elif arg == "--seed-only":
         seed_only = True
+    elif arg == "--vnc" or arg.startswith("--vnc="):
+        vnc_listen = arg.partition("=")[2] or "127.0.0.1:0"
+        if ":" not in vnc_listen:
+            vnc_listen += ":0"
     elif arg == "--install-from-iso":
         install_from_iso = True
     elif arg == "--install-from-img":
@@ -391,8 +399,13 @@ if installing:
 
 # cocoa shows the guest at its own resolution. Append ,zoom-to-fit=on (via
 # WIN11_VM_DISPLAY) to stretch a low-resolution screen to the window.
-display_backend = env("WIN11_VM_DISPLAY") or (
+display_backend = (f"vnc={vnc_listen}" if vnc_listen else env("WIN11_VM_DISPLAY") or (
-    "cocoa" if platform.system() == "Darwin" else "gtk")
+    "cocoa" if platform.system() == "Darwin" else "gtk"))
+if vnc_listen:
+    vnc_host, _, vnc_display = vnc_listen.rpartition(":")
+    if not vnc_display.isdigit():
+        die(f"--vnc display number must be an integer: {vnc_listen}", 2)
+    print(f"VNC: connect to {vnc_host or '127.0.0.1'}:{5900 + int(vnc_display)}")
 
 # Most of the VM definition lives in the QEMU config template; fill in the
 # file paths and hand the rendered file to QEMU with -readconfig.