 Causal projection along a spacelike circular fiber

For $g=q+C(d\psi +A{)}^2$ with $C>0$, projection of every causal curve is causal for $q$, since $q(\dot{\gamma },\dot{\gamma })\le g(\dot{\gamma },\dot{\gamma })\le 0$. Conversely, the lift defined by $d\psi =-A$ along any given base curve has the same norm as that curve. Thus the orbit-space metric $q$ describes the projected causal structure exactly. A Penrose diagram suppressing that circle is a quotient diagram, not the metric of a constant-$\psi$ slice.