How to make the theorem environment flow around campa's code for TeXbook's bend symbol?

Question

This is a follow up question to this comment. How can I make campa's code for TeXbook's bend symbol work with the theorem environment?

Consider the following LaTeX code which I saved in a file called test.tex:

\documentclass{scrartcl}
\usepackage{tikz}
\newenvironment{mydanger}[1]{%
  \sbox0{%
     \begin{tikzpicture}[scale=.3]
        \draw[rounded corners=.1] (-.05,-1.5)--++(0,2.55)--++(.1,0)--++(0,-2.55);
        \draw[fill=white,rounded corners=1] (0,1)--(1,0)--(0,-1)--(-1,0)--cycle;
        \draw[very thick](-.3,-1.5)--(.3,-1.5);
        \node at (0,0) {\small#1};
     \end{tikzpicture}
  }%       this space ^^^ is here for a reason!
  \par\medskip  \noindent
  \hangindent\wd0
  \parindent\hangindent
  \hangafter=-2
  \setbox0=\hbox to0pt{\hss\lower3ex\box0}%
  \dp0=0pt
  \box0
  \small
  \ignorespaces
 }{\par\smallskip}
\newtheorem{theorem}{Theorem}
\usepackage{lipsum}
\begin{document}
\begin{mydanger}{A}
\lipsum[1]
\end{mydanger}
\vspace{1cm}
\begin{mydanger}{A}
\begin{theorem}
\lipsum[1]
\end{theorem}
\end{mydanger}
\end{document}

When I run this code with lualatex test, the following output is typeset:

I'd like the theorem paragraph to flow around the bend symbol like the regular paragraph above it.

---

Important requirement

The solution must be consistent with the possibility of adding margin notes via \marginpar inside the theorem. Therefore, for instance, a solution that encapsulates the theorem inside an invisible tcolorbox will not be an acceptable solution; see here.

Answer 1

This is a rather hacking solution. The implementation of theorem uses trivlist, which starts a new line. Basically what I did is to use \patchcmd to remove trivlist and redefine the \item command to make sure the output is consistent.

\documentclass{scrartcl}
\usepackage{tikz}
\usepackage{etoolbox}
\newenvironment{mydanger}[1]{%
  \sbox0{%
     \begin{tikzpicture}[scale=.3]
        \draw[rounded corners=.1] (-.05,-1.5)--++(0,2.55)--++(.1,0)--++(0,-2.55);
        \draw[fill=white,rounded corners=1] (0,1)--(1,0)--(0,-1)--(-1,0)--cycle;
        \drawvery thick--(.3,-1.5);
        \node at (0,0) {\small#1};
     \end{tikzpicture}
  }%       this space ^^^ is here for a reason!
  \par\medskip  \noindent
  \hangindent\wd0
  \parindent\hangindent
  \hangafter=-2
  \setbox0=\hbox to0pt{\hss\lower3ex\box0}%
  \dp0=0pt
  \box0
  \small
  \ignorespaces
 }{\par\smallskip}
\newtheorem{theorem}{Theorem}
\usepackage{lipsum}
\makeatletter
\patchcmd{@begintheorem}{\trivlist\item}{\bgroup\myitem}{}{\GenericError{}{unable to patch command}{}{}}
\patchcmd{@opargbegintheorem}{\trivlist\item}{\bgroup\myitem}{}{\GenericError{}{unable to patch command}{}{}}
\def@endtheorem{\egroup}
\def@opargendtheorem{\egroup}
\def\myitem[#1]{#1~}
\makeatother
\begin{document}
\begin{mydanger}{A}
\lipsum[1]
\end{mydanger}
\vspace{1cm}
\begin{mydanger}{A}
\begin{theorem}
\lipsum[1]
\end{theorem}
\end{mydanger}
\begin{mydanger}{B}
\begin{theorem}[Test Theorem]
\lipsum[1]
\end{theorem}
\end{mydanger}
\end{document}

\documentclass{scrartcl}
\usepackage{tikz}
\usepackage{etoolbox}
\usepackage{adjustbox}

\newenvironment{mydanger}[1]{%
  \sbox0{%
     \begin{tikzpicture}[scale=.3]
        \draw[rounded corners=.1] (-.05,-1.5)--++(0,2.55)--++(.1,0)--++(0,-2.55);
        \draw[fill=white,rounded corners=1] (0,1)--(1,0)--(0,-1)--(-1,0)--cycle;
        \draw[very thick](-.3,-1.5)--(.3,-1.5);
        \node at (0,0) {\small#1};
     \end{tikzpicture}
     \hspace*{3mm}
  }%       this space ^^^ is here for a reason!
  \par\medskip  \noindent
  \hangindent\wd0
  \parindent\hangindent
  \hangafter=-2
  \setbox0=\hbox to0pt{\hss\lower3ex\box0}%
  \dp0=0pt
  \box0
  \small
  \ignorespaces
 }{\par\smallskip}
\newtheorem{theorem}{Theorem}
\usepackage{lipsum}

\makeatletter
\patchcmd{\@begintheorem}{\trivlist\item}{\bgroup\myitem}{}{\GenericError{}{unable to patch command}{}{}}
\patchcmd{\@opargbegintheorem}{\trivlist\item}{\bgroup\myitem}{}{\GenericError{}{unable to patch command}{}{}}

% also remove the spacing before Theorem
\patchcmd{\@begintheorem}{\hskip\labelsep}{}{}{\GenericError{}{unable to patch command}{}{}}
\patchcmd{\@opargbegintheorem}{\hskip\labelsep}{}{}{\GenericError{}{unable to patch command}{}{}}

\def\@endtheorem{\egroup}
\def\@opargendtheorem{\egroup}
\def\myitem[#1]{\noindent {#1}~}
\makeatother



\begin{document}

\makeatletter
\meaning\@begintheorem
\makeatother

\begin{mydanger}{A}
\lipsum[1]
\end{mydanger}

\vspace{1cm}

\begin{mydanger}{A}
\begin{theorem}
\lipsum[1]
\end{theorem}
\end{mydanger}

\begin{mydanger}{B}
\begin{theorem}[Test Theorem]
\lipsum[1]
\end{theorem}
\end{mydanger}

\end{document}