Emulating the `\shortintertext` command in text mode

I am trying to reduce the spacing between an align and gather environment using the \shortintextext command.I am aware of one solution that nests the align block inside the gather environment to achieve this.However, I am also interested in using \displaybreak (or allowdisplaybreaks) in the align environment, which becomes impossible if align is nested in gather, as it is then wrapped in an unbreakable box.

I am therefore wondering how one could define a text mode version of \shortintertext?

Below is an example that illustrates the issue by causing a large blank space to appear on the first page due to the unbreakable align:

\documentclass{article}\usepackage[a6paper]{geometry}\usepackage{mathtools}\usepackage{blindtext}\allowdisplaybreaks\begin{document}\blindtext\begin{gather}    \begin{align}        a &= b, \\        a &= b, \\        a &= b, \\        a &= b, \\        a &= b, \\        a &= b, \\        a &= b, \\        a &= b,    \end{align}    \shortintertext{where}    a = b.\end{gather}\end{document}