Slightly modfied:
\setuppapersize[S6][S6]
\setupbodyfont[14.4pt]
\setuplayout
[width=360pt,
headerheight=7pt,
footerheight=7pt,
margin=0pt,
backspace=25pt,
topheight=7pt,
bottomheight=7pt,
rightedgedistance=20pt,
rightedge=180pt]
\setuplist[chapter,section][aligntitle=yes,criterium=all]
\setuplist[chapter][align=middle]
\setuphead[chapter][number=yes]
\setuphead[section][number=no]
\setupbackgrounds[text][rightedge][frame=on]
\setupinteraction[
state=start,
menu=on,
page=yes]
\setupnarrower[left=1pt,right=1pt]
\defineinteractionmenu[myMenu][right]
\startinteractionmenu[myMenu]
\placecontent[
criterium=all,
alternative=b,
style={\switchtobodyfont[small]\setupinterlinespace[line=2.4ex]},
interaction=all,
before={\blank[small]\startnarrower},
after={\stopnarrower\blank[medium]},
]
\stopinteractionmenu
\setupinteractionmenu[myMenu][state=start]
\setupinteractionmenu[right][distance=overlay]
\starttext
\chapter{This Long Chapter Title}
\section{This Long Section Title A}
\input knuth
\section{This Long Section Title B}
\input zapf
\stoptext