TeX's hpack routine packages an hlist into a box. While doing that it looks at a global pointer
adjust_tail and if that is not "null" it migrates some nodes to a separate list starting at
adjust_head. This way material from
\vadjust migrates out from the line into the enclosing vertical list during the paragraph building. Otherwise they stay inside the box.
From the luatex manual I was unable to see how this effect could be achieved using
node.hpack. Luatex knows
tex.lists.pre_adjust_head(whatever that is?) but I couldn't quite see if they correspond to TeX's
adjust_tailor how to indicate that
node.hpackshould do the migrating.
If it can at all (the manual has some notes on
node.hpack having weird side-effects on
\insert and such in some cases).
Reason I'm interested in that is to write my own paragraph builder or adapting Taco's code (that doesn't seem to work in that respect (see question Replacement(s) for TeX's paragraph builder using LuaTeX) and has a few other bugs so that it currently doesn't quite work.
Of course, if worst comes to worst, I guess I could migrate those nodes out manually prior to calling
node.hpack but if possible I would use the internal and have it done for me as that is most certainly faster.