command definition outside \begingroup \endgroup pair not working [closed]

Question

This MWE is from a real case where an error occurs (with a hint about WSF from suffix package, but below the error is different) with \globaldefs=1\relax in a \begingroup \endgroup pair, in order to make \newcommand macros visible outside the pair.

This is main mwe.tex.

\documentclass[a4paper,10pt]{report}

\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{suffix,xargs}

\makeatletter

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Code borrowed from `multitoc.dtx' CTAN /macros/latex/contrib/ms %%
%%% Copyright [1998..1999]  Martin Schr\"oder. All rights reserved. %%
% \write with appropriate handling of |\protect| and |\thepage|; args:
% an output stream, some text to write, and some initialization code.
\newcommandx*\protected@write@immediate[3][3]{%
  \begingroup
    \let\thepage\relax
    #3%
    \let\protect\string
    \edef\reserved@a{\immediate\write#1{#2}}%
    \reserved@a
  \endgroup
  \if@nobreak\ifvmode\nobreak\fi\fi%
}
%%%                                                                 %%  
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\newcommandx\MWE[7][3=mwe,4=-1,5=to,6=newcommand,7=12]{%
    \MWE*[#1][#2]%
    \catcode`\\=#7\catcode`\{=#7\catcode`\}=#7\catcode`\$=#7%
    \catcode`\#=#7\catcode`\^=#7\catcode`\_=#7\catcode`\%=#7%
    \let\@tempa\endlinechar%
    \endlinechar=#4%
    \immediate\read\my@file#5\my@lin@%
    \endlinechar=\@tempa%
    \catcode`\%=14\catcode`\_=8\catcode`\^=7\catcode`\#=6%
    \catcode`\$=3\catcode`\}=2\catcode`\{=1\catcode`\\=0%
    \protected@xdef\my@line{\my@lin@}%
    \protected@write@immediate\my@fil@{%%%%%%%%%%%%%%%%%%%%%
\@backslashchar#6\@backslashchar#3\@charlb\my@line\@charrb}%
    \MWE*%
    \input{#2}%
    \MWE*[#1]%
}

\WithSuffix\newcommandx\MWE*[3][1,2,3=.tex]{%
    \ifx\\#2#3\\%
        \immediate\closeout\my@fil@%
        \immediate\closein\my@file%%
    \else\ifx\\#2\\%
        \immediate\openin\my@file=#1#3%%
    \else%
        \newread\my@file%%
        \immediate\openin\my@file=#1#3%%
        \newwrite\my@fil@%
        \immediate\openout\my@fil@=#2#3%
    \fi\fi%
}

\makeatother

\begin{document}

    \begingroup\inputencoding{ascii}
        \globaldefs=1\relax
        \MWE{tst}{tmp}
    \endgroup

    \begingroup\inputencoding{ascii}
        \mwe
    \endgroup

\end{document}

The tst.tex contains just the "Hello world." line.

In the second \begingroup the control sequence \mwe is undefined. Were i to replace \MWE with this

\newcommandx\MWE[7][3=mwe,4=-1,5=to,6=newcommand,7=12]{%
    \newread\my@file%%
    \immediate\openin\my@file=#1.tex%%
    \newwrite\my@fil@%
    \immediate\openout\my@fil@=#2.tex%
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \MWE*[#1][#2]%

    \catcode`\\=#7\catcode`\{=#7\catcode`\}=#7\catcode`\$=#7%
    \catcode`\#=#7\catcode`\^=#7\catcode`\_=#7\catcode`\%=#7%
    \let\@tempa\endlinechar%
    \endlinechar=#4%
    \immediate\read\my@file#5\my@lin@%
    \endlinechar=\@tempa%
    \catcode`\%=14\catcode`\_=8\catcode`\^=7\catcode`\#=6%
    \catcode`\$=3\catcode`\}=2\catcode`\{=1\catcode`\\=0%

    \protected@xdef\my@line{\my@lin@}%
    \protected@write@immediate\my@fil@{%%%%%%%%%%%%%%%%%%%%%
\@backslashchar#6\@backslashchar#3\@charlb\my@line\@charrb}%
    %%%%%%%%%%%%%%%%%%%%%%%%%%%% \MWE*%
    \immediate\closeout\my@fil@%
    \immediate\closein\my@file%%
    \input{#2}%
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \MWE*[#1]%
    \immediate\openin\my@file=#1.tex%
}

the MWE recognizes ok the \mwe command between the two \begingroup \endgroup pairs.

What i want is the same as in the following simplified MWE, but in a different setting; that is, to have a command \mwe available between \begingroup \endgroup pairs.

\documentclass[a4paper,10pt]{report}

\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}

\begin{document}

    \begingroup\inputencoding{ascii}
        \globaldefs=1\relax
        \newcommand\mwe{Hello world.}
    \endgroup

    \begingroup\inputencoding{ascii}
        \mwe
    \endgroup

\end{document}

Comment out \globaldefs=1\relax and \mwe is undefined in the second pair...

Appreciate your help, Thank s

Using \long\def is not working either.

\newcommandx\MWE[8][3=mwe,4=-1,5=to,6=long,7=12,8=gdef]{%
    \MWEZ[#1][#2]%
    \catcode`\\=#7\catcode`\{=#7\catcode`\}=#7\catcode`\$=#7%
    \catcode`\#=#7\catcode`\^=#7\catcode`\_=#7\catcode`\%=#7%
    \let\@tempa\endlinechar%
    \endlinechar=#4%
    \immediate\read\my@file#5\my@lin@%
    \endlinechar=\@tempa%
    \catcode`\%=14\catcode`\_=8\catcode`\^=7\catcode`\#=6%
    \catcode`\$=3\catcode`\}=2\catcode`\{=1\catcode`\\=0%
    \protected@xdef\my@line{\my@lin@}%
    \protected@write@immediate\my@fil@{%%%%%%%%%%%%%%%%%%%%%
\@backslashchar#6\@backslashchar#8\@backslashchar#3\@charlb\my@line\@charrb}%
    \MWEZ%
    \input{#2}%
    \MWEZ[#1]%
}

\newcommandx\MWEZ[3][1,2,3=.tex]{%
    \ifx\\#2#3\\%
        \immediate\closeout\my@fil@%
        \immediate\closein\my@file%%
    \else\ifx\\#2\\%
        \immediate\openin\my@file=#1#3%%
    \else%
        \newread\my@file%%
        \immediate\openin\my@file=#1#3%%
        \newwrite\my@fil@%
        \immediate\openout\my@fil@=#2#3%
    \fi\fi%
}