[Dev-luatex] unexpected delimiter construction with classic tfm cmex font

There are some images of the output and discussion of the \showlists trace in the stackexchange post at https://tex.stackexchange.com/a/734734/1090 but this plain luatex file \tracingonline1 \showboxdepth10 \immediate\write500{\meaning\Arrowvert} $\Arrowvert + \Big\Arrowvert\showlists $ \expandafter\show\the\textfont3 \bye produces the expected || character with pdftex but a { character with luatex even though both claim to be using the same extension font (cmex10) David