Change biblatex postnote behavior

Question

I want change the biblatex postnote behavior for the numeric style. Combining the numeric style with a lot of numbers in a postnote makes it really confusing to read IMO. The postnote for the \autocite command should appear behind the square brackets inside round brackets like this:

I'm not sure what the correct approach is regarding breakable spaces and so on. I've tried to solution of this question but it did not work for \autocite.

MWE:

\documentclass{scrartcl}
\usepackage{filecontents}
\begin{filecontents}{test.bib}
    @book{mdr,
      title = {Verordnung (EU) 2017/745 \"uber Medizinprodukte},
      author = {{N. N.}},
      date = {2017},
      location = {{Europ\"aisches Parlament, Br\"ussel}}
    }
\end{filecontents}

\usepackage[backend=biber, style=ext-numeric, citestyle=numeric-comp, autocite=inline,]{biblatex}
\addbibresource{test.bib}

\begin{document}

\autocite[Kapitel II, Art. 5, Abs. 3]{mdr}

Desired output: [1](Kapitel II, Art. 5, Abs. 3)

\end{document}

Answer 1

You can redefine both \cite and \parencite from their original

\DeclareCiteCommand{\parencite}[\mkbibbrackets]
  {\usebibmacro{cite:init}%
   \usebibmacro{prenote}}
  {\usebibmacro{citeindex}%
   \usebibmacro{cite:comp}}
  {}
  {\usebibmacro{cite:dump}%
   \usebibmacro{postnote}}

to

\DeclareCiteCommand{\parencite}
  {\bibopenbracket
   \usebibmacro{cite:init}%
   \usebibmacro{prenote}}
  {\usebibmacro{citeindex}%
   \usebibmacro{cite:comp}}
  {}
  {\usebibmacro{cite:dump}%
   \bibclosebracket
   \usebibmacro{postnote}}

which means that the brackets close before the postnote. Then it's just a matter of changing postnotedelim and the postnote format.

Note that these definitions are style-specific and the code here is designed to work with (cite)sytle=numeric-comp. For other styles the code would be slightly tweaked.

\documentclass{scrartcl}
\usepackage[backend=biber,
  bibstyle=ext-numeric, citestyle=numeric-comp,
  autocite=inline,]{biblatex}

\DeclareCiteCommand{\cite}
  {\bibopenbracket
   \usebibmacro{cite:init}%
   \usebibmacro{prenote}}
  {\usebibmacro{citeindex}%
   \usebibmacro{cite:comp}}
  {}
  {\usebibmacro{cite:dump}%
   \bibclosebracket
   \usebibmacro{postnote}}

\DeclareCiteCommand{\parencite}
  {\bibopenbracket
   \usebibmacro{cite:init}%
   \usebibmacro{prenote}}
  {\usebibmacro{citeindex}%
   \usebibmacro{cite:comp}}
  {}
  {\usebibmacro{cite:dump}%
   \bibclosebracket
   \usebibmacro{postnote}}

\DeclareDelimFormat{postnotedelim}{}
\DeclareFieldFormat{postnote}{\mkbibparens{\mkpageprefix[pagination][\mknormrange]{#1}}}

\begin{filecontents}{\jobname.bib}
@book{mdr,
  title        = {Verordnung (EU) 2017/745 über Medizinprodukte},
  author       = {{N. N.}},
  date         = {2017},
  organization = {Europäisches Parlament},
  location     = {Brüssel},
}
\end{filecontents}
\addbibresource{\jobname.bib}

\begin{document}

\autocite[Kapitel~II, Art.~5, Abs.~3]{mdr}

Desired output: [1](Kapitel II, Art. 5, Abs. 3)

\end{document}