Cannot set sbox inside tikz

Question

(updated version after Qrrbrbirlbel's answer: I want to measure tikz nodes)

I'd like to compute the width of the content (tikz multiline node) that I will typeset in a tikz-cd node to adapt the shape of a parent node. However, sbox created inside tikz have zero width, and typesetting a tikzpicture inside it gives me an infinite recursion… any idea why and how to avoid that issue?

MWE:

\documentclass{article}
\usepackage{amsmath}
\usepackage{tikz}
\usepackage{tikz-cd}
\begin{document}
\newsavebox{\tmpbox}
\NewExpandableDocumentCommand{\myNode}{m}{
  \node[inner sep=5pt,fill=green,draw,align=center]{#1};
}
\def\myContentOfInterest{\begin{tikzcd}\myNode{42\and multiple lines};\end{tikzcd}}
\def\myContentOfInterestTikzVersion{\begin{tikzpicture}\myNode{42\and multiple lines};\end{tikzpicture}}
Goal: measure the content of \myContentOfInterest
\sbox\tmpbox{\myContentOfInterest}%
\def\myvalue{\the\dimexpr\the\ht\tmpbox\relax}
Outside tikz: \myvalue
Inside tikz:
\tikzset{
  my style/.style={
    /utils/exec={%
      %%%%% works but too simple:
      % \pgfmathheight{"this works but too simple case"}%
      % \edef\myvalue{\pgfmathresult pt}%
      %%%%% fails (infinite computation):
      % \pgfmathheight{"\noexpand\myContentOfInterestTikzVersion"}%%
      % \edef\myvalue{\pgfmathresult pt}%
      %%%%% fails: issue with infinite recursion \pgf@selectfontorig ->\pgf@selectfontorig 
      % \sbox\tmpbox{\myContentOfInterestTikzVersion}%
      \def\myvalue{\text{What should I do to measure the final node itself?}}
    },
  }
}
\begin{tikzcd}[font={\fontsize{10}{12}\selectfont}]
  \node[my style]{\myvalue};
\end{tikzcd}
\end{document}

Answer 1

My original answer was really dirty, thanks to Qrrbrbirlbel for its great suggestion. The solution was:

      \begin{lrbox}{\tmpbox}% <- this create a box (like savebox but environment)
        \begin{pgfinterruptpicture}% <- this resets the font
          \begin{pgfpicture}%
            \node{foo};%
          \end{pgfpicture}%
        \end{pgfinterruptpicture}%
        %\let\selectfont\pgf@selectfontorig%
      \end{lrbox}%

Example:

\documentclass{article}
\usepackage{amsmath}
\usepackage{tikz}
\usepackage{tikz-cd}
\begin{document}
\newsavebox{\tmpbox}
\NewExpandableDocumentCommand{\myNode}{m}{
  \node[inner sep=5pt,fill=green,draw,align=center]{#1};
}
\def\myContentOfInterestBasic{\myNode{42\and multiple lines};}
\def\myContentOfInterest{\begin{tikzcd}\myContentOfInterestBasic\end{tikzcd}}
Goal: measure the content of \myContentOfInterest
\sbox\tmpbox{\myContentOfInterest}%
\def\myvalue{\the\dimexpr\the\ht\tmpbox\relax}
Outside tikz: \myvalue
\rule{\myvalue}{\myvalue}
\makeatletter
Inside tikz:
\tikzset{
  my style/.style={
    /utils/exec={%
      \begin{lrbox}{\tmpbox}
        \begin{pgfinterruptpicture}%
          \begin{pgfpicture}
            \myContentOfInterestBasic%
          \end{pgfpicture}
        \end{pgfinterruptpicture}%
        %\let\selectfont\pgf@selectfontorig%
      \end{lrbox}%
    },
  },
}
\makeatother
% Works:
\begin{tikzcd}
  \node[my style]{\myvalue};
\end{tikzcd}
% Works:
\begin{tikzcd}[font={\fontsize{18}{12}\selectfont}]
  \node{Test};
\end{tikzcd}
%% Works now
\begin{tikzcd}[font={\fontsize{18}{12}\selectfont}]
  \node[my style]{\myvalue};
\end{tikzcd}
\rule{\myvalue}{\myvalue}
\end{document}