\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}
