\appendtoks
\ifcase\@@svn
% % 0 : unknown
\or
\setsystemmode\v!first % 1 : first run
\or
% % 2 : successive run
\or
\setsystemmode\v!first % 3 : first and only run
\or
\setsystemmode\v!last % 4 : (extra) last run
\fi
\to \everysetupsystem
I suppose that last=4 runs
But the max number of runs is 8 , if I've understood mtx-context.lua
So
\starttext
%%
%% content here
%%
\startmode[LAST]\myNullMacro\stopmode%
\stoptext
#> context mydocument.tex && context --mode=LAST mydocument.tex
ensure that the code inside \startmode[LAST]...\stopmode is really seen the "last " pass
--
luigi