Current texlive-full package fails

Using the pkg downloaded today from the pkg servers.

I took my issue to the tex-live list at tug, and got this information from
David Carlisle:

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Your log shows you are using a prerelease of the June 2025 latex. A current
texlive starts

LaTeX2e <2025-06-01> patch level 1

not

LaTeX2e <2025-06-01> pre-release-2 (develop 2025-6-24 branch)

Note this list reaches the maintainers of the upstream texlive, if your
linux distribution is distributing an older version, especially a
pre-release version then you need to take it up with them. Note the
pre-release version should only have been installed as pdflatex-dev  not
pdflatex.
=========================================================

Here's a repeatable example:

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\documentclass{amsbook}

\begin{document}
\chapter{chapter}
\section{Algebraic}

foo bar

\end{document}
========================================

This fails with:

===========================================================================
This is pdfTeX, Version 3.141592653-2.6-1.40.27 (Web2C 2025) (preloaded
format=pdflatex)
 restricted \write18 enabled.
entering extended mode
(./Test.tex
LaTeX2e <2025-06-01> pre-release-2 (develop 2025-7-8 branch)
L3 programming layer <2025-01-18>
(/usr/local/share/texmf-dist/tex/latex/amscls/amsbook.cls
Document Class: amsbook 2020/05/29 v2.20.6
(/usr/local/share/texmf-dist/tex/latex/amsmath/amsmath.sty
For additional information on amsmath, use the `?' option.
(/usr/local/share/texmf-dist/tex/latex/amsmath/amstext.sty
(/usr/local/share/texmf-dist/tex/latex/amsmath/amsgen.sty))
(/usr/local/share/texmf-dist/tex/latex/amsmath/amsbsy.sty)
(/usr/local/share/texmf-dist/tex/latex/amsmath/amsopn.sty))
(/usr/local/share/texmf-dist/tex/latex/amsfonts/umsa.fd)
(/usr/local/share/texmf-dist/tex/latex/amsfonts/amsfonts.sty))
(/usr/local/share/texmf-dist/tex/latex/l3backend/l3backend-pdftex.def)
(./Test.aux) (/usr/local/share/texmf-dist/tex/latex/amsfonts/umsa.fd)
(/usr/local/share/texmf-dist/tex/latex/amsfonts/umsb.fd)
Chapter 1
! Undefined control sequence.
\@secmark ...t \@nilgobble \@temptokena \@themark
                                                  {}\@nil \edef \@tempa
{\@n...
l.4 \chapter{chapter}

? x
No pages of output.
Transcript written on Test.log.

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