Biblatex footnote citation: reference same citation previous footnote number

Question

I've been getting into LaTeX for a thesis and I'm overall pretty satisfied with my setup. There's however an issue I can't wrap my head around, and can't find a solution for. Using Biber and biblatex, with verbose-trad1 as an option, I'd like that whenever opcit is called, instead of the output being

{Author} op. cit.

it be

{Author} op. cit. #REF

where #REF refers to the footnote number where the citation first appeared.

Here's a M(n)WE:

%!TEX program = xelatex
% Add packages
\documentclass[12pt]{article}
\usepackage[english,main=french]{babel}
\usepackage{fontspec}
\usepackage[autostyle=true]{csquotes}
\usepackage[citestyle=ext-verbose-trad1, articlein=false, bibstyle=ext-authortitle]{biblatex}
\addbibresource{ref.bib}
\usepackage{hyperref}

% Citation settings
\DefineBibliographyStrings{french}{opcit = {\textit{supra}, note \ref{}},} %<= I guess it'd go there?

% Test proper
\begin{document}
    Some text string\autocite{A}, some other\autocite{B}, some more\autocite{A}.
\end{document}

Where I'd like the footnote output to be:

1. Author A, full reference
2. Author B, full reference
3. Author A, supra, note 1.

This answer would work but it'd be incredibly tedious and could only be done at the end, once citations are set in stone, which defeats the purpose of a language like LaTeX. In any case, I'm in over my head.

Answer 1

If you just a want a verbose style with references to the first footnote and 'ibidem' you can use (ext-)verbose-inote.

\documentclass[12pt]{article}
\usepackage[english,main=french]{babel}
\usepackage[autostyle=true]{csquotes}
\usepackage{fontspec}
\usepackage[style=ext-verbose-inote, articlein=false]{biblatex}
\usepackage{hyperref}

\DefineBibliographyStrings{french}{
  seenote = {supra, note},
}

\addbibresource{biblatex-examples.bib}


\begin{document}
  Some text string\autocite{sigfridsson},
  some other\autocite{worman},
  some more\autocite{sigfridsson}.
\end{document}

---

If you want to retain all the other scholarly abbreviations of verbose-trad1, some more work is needed. In this example I only replace op cit. not loc. cit. or any other abbreviation.

\documentclass[12pt]{article}
\usepackage[english,main=french]{babel}
\usepackage[autostyle=true]{csquotes}
\usepackage{fontspec}
\usepackage[style=ext-verbose-trad1, articlein=false]{biblatex}
\usepackage{hyperref}

\DefineBibliographyStrings{french}{
  seenote = {supra, note},
}

\newtoggle{cbx:pageref}

\DeclareBibliographyOption[boolean]{pageref}[true]{%
  \settoggle{cbx:pageref}{#1}%
  \iftoggle{cbx:pageref}
    {\ExecuteBibliographyOptions{pagetracker}}
    {}}

\DeclareFieldFormat{bibhyperlink}{%
  \bibhyperlink{%
    \thefield{entrykey}:\csuse{cbx@\iffootnote{f}{t}@\thefield{entrykey}}}{#1}}
\DeclareFieldFormat{bibhypertarget}{%
  \bibhypertarget{\thefield{entrykey}:\the\value{instcount}}{#1}}

\providecommand*{\mkibid}[1]{#1}

\renewbibmacro*{cite:save}{%
  \csxdef{cbx@lastcite@\thefield{entrykey}}{\the\value{instcount}}%
  \iffootnote
    {\csxdef{cbx@f@\thefield{entrykey}}{\the\value{instcount}}%
     \label{cbx@\the\value{instcount}}}
    {}%
  \global\boolfalse{cbx:noidem}}

\newbibmacro{seenote}{%
  \printtext{%
    \bibstring{seenote}\addnbspace
    \ref{cbx@\csuse{cbx@f@\thefield{entrykey}}}%
    \iftoggle{cbx:pageref}
      {\ifsamepage{\the\value{instcount}}
                  {\csuse{cbx@f@\thefield{entrykey}}}
         {}
         {\addcomma\space\bibstring{page}\addnbspace
          \pageref{cbx@\csuse{cbx@f@\thefield{entrykey}}}}}
      {}}}

\renewbibmacro*{cite:opcit}{%
  \iffootnote
    {\usebibmacro{seenote}}
    {\printtext[bibhyperlink]{\bibstring[\mkibid]{opcit}}}}

\addbibresource{biblatex-examples.bib}


\begin{document}
  Some text string\autocite{sigfridsson},
  some other\autocite{worman},
  some more\autocite{sigfridsson}.
\end{document}