Advertise zwlr_output_manager_v1 with the single head, published on
setup and re-published from the commit path whenever the size lands
(resizes apply lazily, so the commit -- not the request -- is where
the new size becomes observable).
Client sizes apply standalone through the normal resize path (tabs
reflow, swapchain follows); nested refuses anything but the live
size since the host owns the geometry. Disabling, scale and
transform changes are refused; superseded configs are destroyed
after feedback.
Standalone output_resize now owns the canvas size so client resizes
reach the lazy modeset. wltest gains --output-mgmt; smoke tests
cover the global, head listing, and an 800x600 apply with tab
reflow.