[luatex] pre_output_filter: How to get the vertical list of the full page?

[Henri Menke]

Dear list,

It seems as if the pre_output_filter only gives you the nodes in the
body block but without the \headline and \footline.  I would have
expected that those are included because \plainoutput performs

   \shipout\vbox{\makeheadline\pagebody\makefootline}

and I would have expected to get the vlist defined by the above \vbox
inside the callback.  Am I doing it wrong or am I using the wrong callback?

Cheers, Henri