biblatex, backend=bibtex TeX-output-dir not nil, cannot compile bibtex

[Uwe Brauer]

* biblatex, backend=bibtex TeX-output-dir not nil, cannot compile bibtex
Hi all (especially  Al whom I put in the CC just in case)

I am on Ubuntu 24.04, emacs 29.4 pulled and compiled the latest auctex from the 
git repository 
with commit b474c139fa080f06.

If TeX-output-dir is set to nil then the following two MWE (which I have also 
for convenience attached)

--8<---------------cut here---------------start------------->8---
\documentclass[12pt,reqno]{amsart}
\usepackage[colorlinks,citecolor=blue]{hyperref}
%\usepackage[backend=biber,style=alphabetic,citestyle=alphabetic,backref]{biblatex}
 
\usepackage[backend=bibtex,style=alphabetic,citestyle=alphabetic,backref]{biblatex}
\addbibresource{test.bib}
\begin{document}
\cite{nordstrom13:_zur_theor_gravit_stand_relat% Nordström 1913, Annalen der 
Physik 43, 533
}
\printbibliography
\end{document}
--8<---------------cut here---------------end--------------->8---


--8<---------------cut here---------------start------------->8---
@Article{nordstrom13:_zur_theor_gravit_stand_relat,
  title        = {Zur {T}heory der {G}ravitation vom {S}tandpunkt des
                  {R}elativitätsprinzip},
  author       = {Nordström, G.},
  journal      = {Annalen der Physik},
  year         = 1913,
  pages        = {533-554},
  volume       = 43
}
--8<---------------cut here---------------end--------------->8---

work in the sense, that 

    1) if 
\usepackage[backend=biber,style=alphabetic,citestyle=alphabetic,backref]{biblatex}
       is used, then
       a) running latex (pdflatex)
       b) running biber
       c) running latex (pdflatex)
          works
    2) if 
\usepackage[backend=bibtex,style=alphabetic,citestyle=alphabetic,backref]{biblatex}
       is used, then
       a) running latex (pdflatex)
       b) running bibtex
       c) running latex (pdflatex)
          works

However if TeX-output-dir is set to "build"

Then the backend=biber works, but backend=bibtex gives the following error when 
running  bibtex

I couldn't open database file test-bib-blx.bib
--8<---------------cut here---------------start------------->8---

---line 6 of file build/test-bib.aux
 : \bibdata{test-bib-blx
 :                      ,test}
I'm skipping whatever remains of this command
I found no database files---while reading file build/test-bib.aux
Warning--I didn't find a database entry for "biblatex-control"
Warning--I didn't find a database entry for 
"nordstrom13:_zur_theor_gravit_stand_relat"
Biblatex version: 3.19
(There were 2 error messages)

--8<---------------cut here---------------end--------------->8---


Any idea how to solve this?

Regards

Uwe Brauer 


@Article{nordstrom13:_zur_theor_gravit_stand_relat,
  title        = {Zur {T}heory der {G}ravitation vom {S}tandpunkt des
                  {R}elativitätsprinzip},
  author       = {Nordström, G.},
  journal      = {Annalen der Physik},
  year         = 1913,
  pages        = {533-554},
  volume       = 43
}

\documentclass[12pt,reqno]{amsart}
\usepackage[colorlinks,citecolor=blue]{hyperref}
%\usepackage[backend=biber,style=alphabetic,citestyle=alphabetic,backref]{biblatex} 
\usepackage[backend=bibtex,style=alphabetic,citestyle=alphabetic,backref]{biblatex}
\addbibresource{test.bib}
\begin{document}


\cite{nordstrom13:_zur_theor_gravit_stand_relat% Nordström 1913, Annalen der Physik 43, 533
}

\printbibliography
\end{document}

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