The Qemu Spice user manual makes reference to a "dynamic resolution" feature. If I'm understanding correctly, this alters the guest resolution to match the size of the VM's window, as is done automatically by VirtualBox's guest extensions.
I've skimmed every piece of Spice user documentation I can find. Nothing I've read actually addresses making this work in a Windows guest... although this one suggests that it works with an X11-based client.
What are the steps to enable dynamic resolution in a Windows 7 guest?