shipout2-008.lvt

\RequirePackage[enable-debug]{expl3}
\ExplSyntaxOn
\debug_on:n { check-declarations , deprecation }
\ExplSyntaxOff

\documentclass[oneside]{report}

\input{regression-test}

\newbox\chapteropeningbox

\newcommand\chapteropening[1]{%
    \setbox\chapteropeningbox\vbox{\hsize\textwidth #1}}

\AddToHook{shipout/before}{%
% before first page only generate a verso page if there is actual material
  \ifnum \ReadonlyShipoutCounter = 0
    \ifvoid\chapteropeningbox \else
      \RawShipout\vbox to\textheight{\vss \usebox\chapteropeningbox \vss}%
   \fi
 \else
 % later do it always
   \RawShipout\vbox to\textheight{\vss \usebox\chapteropeningbox \vss}%
 \fi
}


\DebugShipoutsOn

\begin{document}

\DebugHooksOn

\START

\chapter{A}
%\chapteropening{ \centering \Huge FOO1 }

1 some text \newpage
2 some text \newpage
3 some text \newpage

\chapter{B}
\chapteropening{ \centering \Huge FOO2 }

4 some text 

\chapter{C}

5 some text \newpage
6 some text 



\end{document}