    \documentclass{article}

    \usepackage{agda}

    \begin{document}

    \begin{AgdaAlign}
    \begin{code}
    module Issue2733-2 where
    \end{code}

    Indentation should be inserted before \AgdaKeyword{postulate}, but not
    before the last occurrence of \AgdaPrimitiveType{Set}, which should be
    aligned with the penultimate occurrence of \AgdaPrimitiveType{Set}:
    \begin{code}
      postulate
        A  : Set
        B  : Set →
             Set
    \end{code}
    \end{AgdaAlign}

    \end{document}