Suppose this file:

--------------

\immediate\openout0=test.ref

\setbox13=\hbox{aha}
\showbox13

\end

--------------

If I run "luatex file", it ends without errors and the \showbox result
is written in the test.ref file.

But if the \openout line is commented or it is opened another output
stream than zero, then the behavior is correct: it ends with:

----------------

! OK (see the transcript file).
l.5 \showbox13

?

----------------

luatex --credits:

This is LuaTeX, Version 1.15.0 (TeX Live 2022)

...

Development id: 7503

The luatex from TL2021 (id 7430) does have this problem, i.e the
\showbox result is in transcript file always.

Regards

Petr Olsak