multicol breaks float code

[u-fischer]

The multicol package redefines inside the multicols environment \end@dblfloat and this breaks the handling of double column floats. They produce warnings and circular parent-kid references and the floats are lost.

This here seems to fix it. The kernel should provide tagging sockets, so that multicol can add them:

\DocumentMetadata{%
	%pdfstandard=A-4f,
	pdfversion=2.0,
	lang=en,
	testphase={phase-III},
    uncompress
}
\documentclass{article}
\usepackage{multicol}
\makeatletter
\def\set@floatcmds{%
 \let\@dblfloat\@dbflt
 \def\end@dblfloat{\@endfloatbox
   \@nameuse{__tag_float_end:}%missing
   \@largefloatcheck
   \outer@nobreak
   \ifnum\@floatpenalty<\z@
     \@cons\@deferlist\@currbox
   \fi
   \ifnum\@floatpenalty=-\@Mii
     \@Esphack
     \@nameuse{__tag_float_start_par:}%missing
   \fi}}
\begin{document}
\begin{multicols}{2}
hallo

\begin{table*}
a large table
\end{table*}
Welt
\end{multicols}
\end{document}