How to prevent parts of source from being automatically indented?

Question

EDIT Rephrased question to be more abstract and less specific to only fragile-frames.

Context:

While recompiling a presentation, the process halted with err-msg

file ended while scanning use of next.

During debugging the whole thing I found indented fragile-frames, although they weren't supposed to be.

I assume, TeXstudio might have indented the code as part of the code folding routine.

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Problem: How do I prevent parts of source code from being automatically indented? How can arara or latexindent be utilized for this purpose?

A minimalistic WE using fragile-frame to exemplify the problem:

\documentclass{beamer}

\usepackage{listings}

\begin{document}

%not to be indented by texstudio!
\begin{frame}[fragile]{a title}
some explanation to the snippet
\begin{lstlisting}[caption=func foo not bar,label=fct:foo]
foo(a,b,c)
    c = a + b
    return c
\end{lstlisting}
\end{frame}

%allowed to be indented.
   \begin{frame}{smart title}
   some input
   \end{frame}

\end{document}