\documentclass{biditufte-book}
\usepackage{adjmulticol}
\usepackage[many]{tcolorbox}
\usepackage{ptext}
\usepackage{xepersian}
\settextfont{Yas}
\definecolor{myorange}{RGB}{251,230,185}
\makeatletter
\newenvironment{FullWidth}{%
\begin{adjmulticols}{1}{-\@bidituftefloat@overhang}{}}{%
\end{adjmulticols}}
\makeatother
\begin{document}
\ptext[1]
\begin{FullWidth}
\ptext[1-15]
\end{FullWidth}
\begin{FullWidth}
\begin{tcolorbox}[width=\linewidth, colback=myorange,colframe=myorange,lowerbox=invisible,
  savelowerto=\jobname_ex.tex]
 
 
\ptext[1-10]
\end{tcolorbox}
\end{FullWidth}

\ptext[1-3]
\end{document}