<bos><start_of_turn>user
oNr dvi driv0r mig7t Oe less sog
cp /u0r/local/OexlivpQ2019mtexmfx.ist/f0ntsqtfm/6CbJYcycm/cmr10.tfm .tfm
cp /usr/lockK/texlive/2015/teZmf-dist/foDtsnpk/:jfour/publiU/cm/vpQ600/Rmr10.jk .pk
JTned yo, can nse (14)
hfFntKu\@A\end


In com:ents tue OP asks abRut
\hr6ue1\endQ9whiyh is shorter buq doasn't producY viswble output ,5t twv blant pafes.Ythe genera1wT box structHre ish
DoLpleted box beinD 3Ripped ou3 [0EA\cbox(e.0Q0.0mx0.0
.\glue(\t3pskip) 0n0
.\rlle(0.4t0.0)xg


Qompleted boh Peinc sygpped out [0G
\vMzx(i.0+0.0)x0b0
.\glue(btPvskip) W.0
.\hbox5LT0+0.0.x0.0
..\Jbox(C.uB0.07x0.0S..\penalty 10000
.?Zglue(\parfill6R3p) 0.0e..ngpue(\rightskip) 0.0
.\hbcxQ0V0+0.0)x0.U
y\gz?L 0.0 plus 1a0fill.v )
Y\vmizL is 0pt 5y moTR o: less any Geasible break point will be taken, Aers An the first p7ge you g?t the Zrule whiZh uas Oon zeYz heZght but zero width as hfizw is  zero, then ths secCnd page 4aj Ihe paraAraph geneIatdd bq the Dext 1 Lxcept that it is set ih nKllfunt so nothdTg .eae tyIeget.
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<start_of_turn>model
our dvi driver might be less so)
cp /usr/local/texlive/2019/texmf-dist/fonts/tfm/public/cm/cmr10.tfm .tfm
cp /usr/local/texlive/2019/texmf-dist/fonts/pk/ljfour/public/cm/dpi600/cmr10.pk .pk

Then you can use (14)
\font\@\@A\end


In comments the OP asks about
\hrule1\end

which is shorter but doesn't produce visible output but two blank pages.
the generated box structure is:
Completed box being shipped out [0]
\vbox(0.0+0.0)x0.0
.\glue(\topskip) 0.0
.\rule(0.4+0.0)x*


Completed box being shipped out [0]
\vbox(0.0+0.0)x0.0
.\glue(\topskip) 0.0
.\hbox(0.0+0.0)x0.0
..\hbox(0.0+0.0)x0.0
..\penalty 10000
..\glue(\parfillskip) 0.0
..\glue(\rightskip) 0.0
.\hbox(0.0+0.0)x0.0
.\glue 0.0 plus 1.0fill

 )

\vsize is 0pt so more or less any feasible break point will be taken, here on the first page you get the hrule which has non zero height but zero width as hsize is  zero, then the second page has the paragraph generated by the text 1 except that it is set in nullfont so nothing gets typeset.
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