    \documentclass{article}

    \usepackage{agda}

    \begin{document}

    \noindent Before.
    \begin{AgdaMultiCode}
    \begin{code}[hide]
      postulate
    \end{code}
    \begin{code}
        A    : Set
    \end{code}
    \begin{code}
        BBB  : Set
    \end{code}
    \end{AgdaMultiCode}
    After.

    \noindent Before.
    \begin{AgdaAlign}
    \begin{code}
      postulate
        C : Set
    \end{code}
    \begin{code}[hide]
        D : Set
    \end{code}
    \begin{code}
        E : Set
    \end{code}
    \end{AgdaAlign}
    After.

    \noindent Before.
    \begin{AgdaAlign}
    \begin{code}
      postulate
        F : Set
    \end{code}
    In between.
    \begin{AgdaSuppressSpace}
    \begin{code}
      postulate
        G : Set
    \end{code}
    \begin{code}[hide]
      postulate
    \end{code}
    \begin{code}
        H : Set
    \end{code}
    \end{AgdaSuppressSpace}
    \end{AgdaAlign}
    After.

    \noindent Before.
    \begin{AgdaMultiCode}
    \begin{code}
      postulate
        !_!    : Set → Set
    \end{code}
    \begin{code}[hide]
      postulate
    \end{code}
    \begin{code}
        <!_!>  : Set → Set
    \end{code}
    \end{AgdaMultiCode}
    After.

    \end{document}