Safe footnotemarks and automatically call footnotetext with tcolorbox

The idea is to replace marginpar with marginnote (marginnote package), but only inside tcolorbox. The biggest problem with marginnote is that the notes tends to overlap.

TCBsidenote also uses the global footnote counter instead of mpfootnote.

documentclass[10pt,a4paper]{tufte-book}

usepackage{lipsum}
usepackage[theorems]{tcolorbox}

newtcbtheorem[number within=chapter]{TcbTheorem}{Theorem}{
    colback=blue!5, colframe=blue!5, coltitle=red,
}{thm}

lettuftenote=marginnote
letmarginnoterelax% make compatible
usepackage{marginnote}
letauxmarginpar=marginnote
letmarginnote=tuftenote% restore original

makeatletter
let@sidenotemark@footnotemark
let@sidenotetext@footnotetext
%
longdef@tufte@sidenote[#1][#2]#3{%
  ifthenelse{boolean{@tufte@loadnatbib}}{%
    letcite@tufte@infootnote@cite%   use the in-sidenote cite command
  }{}%
  gdef@tufte@citations{}%           clear out any old citations
  ifthenelse{NOTisempty{#2}}{%
    gsetlength{@tufte@sidenote@vertical@offset}{#2}%
  }{%
    gsetlength{@tufte@sidenote@vertical@offset}{0pt}%
  }%
  ifthenelse{isempty{#1}}{%
    % no specific footnote number provided
    stepcounter@mpfn%
    protected@xdef@thefnmark{thempfn}%
    @sidenotemark@sidenotetext[@tufte@sidenote@vertical@offset]{#3}%
  }{%
    % specific footnote number provided
    begingroup%
      csname c@@mpfnendcsname #1relax%
      unrestored@protected@xdef@thefnmark{thempfn}%
    endgroup%
    @sidenotemark@sidenotetext[@tufte@sidenote@vertical@offset]{#3}%
  }%
  @tufte@print@citations%            print any citations
  ifthenelse{boolean{@tufte@loadnatbib}}{%
    letcite@tufte@normal@cite%       go back to using normal in-text cite command
  }{}%
  unskipignorespaces%               remove extra white space
  kern-multiplefootnotemarker%      remove kern left behind by sidenote
  kernmultiplefootnotemarkerrelax% add new kern here to replace the one we yanked
}
newcommand{TCBsidenote}{def@mpfn{footnote}% setup
  letthempfn=thefootnote
  letmarginpar=auxmarginpar}
makeatother

begin{document}
    begin{TcbTheorem}{Name}{ref}
      TCBsidenote% local setup
        Testsidenote{First}

        Anothersidenote{Second}
    end{TcbTheorem}

end{document}

I got it working. The following does what I want:

RequirePackage{xparse}
RequirePackage{etoolbox}

def@me@blocknotemarks@keys@add#1#2{expandafterxdefcsname @me@blocknotemarks@keys@#1endcsname{#2}}
def@me@blocknotemarks@keys@get#1{csname @me@blocknotemarks@keys@#1endcsname}

newcounter{@me@blocknote@size}
newcounter{@me@blocknote@iter}
NewDocumentCommand{bsidenotemark}{}{%
    addtocounter{@me@blocknote@size}{1}footnotemark
    @me@blocknotemarks@keys@add{the@me@blocknote@size}{thefootnote}
} 

NewDocumentCommand{bsidenotetext}{O{0pt}m}{%
    addtocounter{@me@blocknote@iter}{1}
    protected@xdef@thefnmark{@me@blocknotemarks@keys@get{the@me@blocknote@iter}}%
    @footnotetext[#1]{#2}      
}

gdef@me@blocknote@lists@pending{relax} % create empty list
NewDocumentCommand{bsidenote}{O{0pt}m}{%
    bsidenotemark{}%
    % will be executed by bsidenoteprocess
    listgadd{@me@blocknote@lists@pending}{bsidenotetext[#1]{#2}} 
}

NewDocumentCommand{bsidenoteprocess}{}{%
    forlistloop{}{@me@blocknote@lists@pending}
    gdef@me@blocknote@lists@pending{relax} % claer list
}

NewDocumentCommand{bmarginnote}{O{0pt}m}{%
    listgadd{@me@blocknote@lists@pending}{marginnote[#1]{#2}} 
}

newtcbtheorem[number within=chapter]{TcbTheorem}{Theorem}{
    colback=blue!5, colframe=blue, coltitle=blue,
    after={bsidenoteprocess},
}{thm}


begin{document}
begin{TcbTheorem}{}{}
    begin{itemize} 
        item Absidenote{Aa}
        item Bbsidenote[3cm]{Bb}
        item bmarginnote[5cm]{foo}
    end{itemize}
end{TcbTheorem}
end{document}