🚀 go-pugleaf

Here is the present state of the work on the numlines.sty.
I am still a neophite at the workings of boxes but I am learning.
I used newcommand and renewcommand to satisfy the LaTeX purists.
I am trying to copy box255 into box1 with line numbers and putting the
result back into box255 and calling \@outputpage so that LaTeX can
put the inserts and everything else in the way it normally does.
Is this even close to the right approach?  Here is what I have so far:
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\font\sevenrm=cmr7

\newcommand\zeroToSp{\parskip=1sp plus1pt
  \renewcommand\vfil{\vskip1sp plus1fil}
  \renewcommand\vfill{\vskip1sp plus1fill}
  \abovedisplayshortskip=1sp plus3pt
  \postdisplaypenalty=1
  \interlinepenalty=1}

\zeroToSp

\newcount\lineCountInit  % used to establish lineCount of first line on page
\global\lineCountInit=0
\newcount\lineCountInterval  % used to determine how often lineCount is printed
\global\lineCountInterval=5
\newcount\lineCountStart  % don't print lineCount until lineCount reaches this
\global\lineCountStart=1
\newcount\lineCountFinish  % don't print lineCount after this
\global\lineCountFinish=400

\newcount\lineCount
\newcommand\resetlineCount{%
\global\lineCount=\lineCountInit}

\resetlineCount

\newcount\pen \newif\ifAnyleft
\newcommand\dupcount{% duplicate box255 with box1 while counting lines
  \loop \Anyleftfalse
    \ifdim\lastskip=0pt \ifdim\lastkern=0pt \ifnum\lastpenalty=0
      \global\setbox0=\lastbox \ifvoid0 % end of breakup loop
    \else \Anylefttrue                  % box present
      \appendline
      \global\advance\lineCount by 1
      \global\setbox1=\vbox{\box0 \unvbox1}\fi
    \else \Anylefttrue                  % penalty present
      \pen=\lastpenalty
      \global\setbox1=\vbox{\penalty\pen\unvbox1}\unpenalty\fi
    \else \Anylefttrue                  % kern present
      \dimen0=\lastkern
      \global\setbox1=\vbox{\kern\dimen0 \unvbox1}\unkern \fi
    \else \Anylefttrue                  % skip present
      \skip0=\lastskip
      \global\setbox1=\vbox{\vskip\skip0 \unvbox1}\unskip \fi
    \ifAnyleft \repeat}

\newcommand\appendline{% put rest of lineCount logic in later
  \setbox2=\hbox{\vrule height\ht0 depth\dp0 width0pt \sevenrm\the\lineCount}
  \global\advance\lineCount-1
  \ifodd\count0\global\setbox1=\vbox{\unvbox1 \box2} % oddeven logic
     \else\global\setbox1=\vbox{\box2 \unvbox1}\fi}

\newbox\brk
\output={%
         \setbox\brk=\vbox{\unvcopy255 \dupcount}
         \ifdim\ht\brk>0pt \message{Incomplete breakup} \fi
         \setbox255=\vbox to\vsize{\unvbox1}
         \@outputpage}
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-- 
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Oakland University             - until you know the truth.  Then there's
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