Breaking tcolorboxes with parcolumns

Question

I tried to extend this class with breakable tcolorboxes.
For some reason this does not work at all.
Here is my .cls file where I marked my change:
ProvidesClass{cornell}
LoadClass[a4paper]{article}
usepackage{tcolorbox}
tcbuselibrary{breakable,skins,xparse}
usepackage{parcolumns} % Used to create two columns
usepackage{bookmark} % Add bookmarks to the resulting PDF
usepackage[margin=2cm]{geometry} % Change geometry of pages
usepackage{hyperref} % Default hyperref setup
hypersetup{
    colorlinks   = true, % Colour links instead of ugly boxes
    urlcolor     = blue, % Colour for external hyperlinks
    linkcolor    = blue, % Colour of internal links
    citecolor    = red   % Colour of citations
}

date{}

renewcommand{maketitle}{%
    vspace{-3em}
    pdfbookmark[0]{@title}{title}
    begin{tcolorbox}[width=textwidth,lowerbox=invisible]
        Hugesffamily @title
    end{tcolorbox}
    vspace{2em}
}

DeclareDocumentCommandpreread{ m m }
{
    pdfbookmark[1]{Introduction}{intro}
    begin{tcolorbox}[width=textwidth]
        #1
        tcblower
        #2
    end{tcolorbox}
}

DeclareDocumentCommandnote{ o m }
{
    IfNoValueT{#1} {
        vspace{-1.5em}
    }{}
    begin{parcolumns}[colwidths={1=.33textwidth},nofirstindent]{2}
        colchunk{
            IfNoValueF{#1} {
                pdfbookmark[1]{#1}{note}
                begin{tcolorbox}[lowerbox=invisible,box align=top]
                    #1
                end{tcolorbox}
            }{}
        }
        colchunk{
            begin{tcolorbox}[enhanced,lowerbox=invisible,box align=top,breakable] % <<< HERE I ADDED BREAKABLE
                #2
            end{tcolorbox}
        }
    end{parcolumns}
}
DeclareDocumentCommandsummary{ m }
{
    vfill
    pdfbookmark[1]{Summary}{summary}
    begin{tcolorbox}[
        enhanced,
        floatplacement=!b,
        float,
        colframe=black,
        colupper=black,
        opacitybacktitle=1,
        opacitytext=1,
        segmentation style={black!55,solid,opacity=0,line width=3pt},
        title=Summary,
        fonttitle=largebfseriessffamily]
        #1
    end{tcolorbox}
}

And here is a sample file:
documentclass{cornell}

usepackage{lipsum}

title{A topic we're taking notes on}

begin{document}
maketitle

preread
    {Questions}
    {
        begin{enumerate}
            item{What's the first question this section will answer?}
            item{What's the second question?}
        end{enumerate}
    }

note[Some key term]
{
    begin{itemize}
        item{A cool thing}
        item{Another cool thing}
        item{Not all things are cool}
    end{itemize}
}

note[Another term]
{
    lipsum[4]
}
note{lipsum[5]}
note{lipsum[6-7]}

summary{A fabulous summary.}

note{lipsum[6]}
note{lipsum[9-12]}
note{lipsum[10-20]}

end{document}

When compiling this the results are really awkward.
Here should be a break across the two pages:

Here are actually breaks within a single page:

Does anyone know how to solve this issue?

Ignasi · Accepted Answer

I suggest to replace parcolumns package by paracol into cornell.cls.
May be you need some more adjustments, but following code worked for me:
ProvidesClass{cornell}
LoadClass[a4paper]{article}
usepackage{tcolorbox}
tcbuselibrary{breakable,skins,xparse}
usepackage{paracol} % Used to create two columns
usepackage{bookmark} % Add bookmarks to the resulting PDF
usepackage[margin=2cm]{geometry} % Change geometry of pages
usepackage{hyperref} % Default hyperref setup
hypersetup{
    colorlinks   = true, % Colour links instead of ugly boxes
    urlcolor     = blue, % Colour for external hyperlinks
    linkcolor    = blue, % Colour of internal links
    citecolor    = red   % Colour of citations
}

date{}

renewcommand{maketitle}{%
    vspace{-3em}
    pdfbookmark[0]{@title}{title}
    begin{tcolorbox}[width=textwidth,lowerbox=invisible]
        Hugesffamily @title
    end{tcolorbox}
    vspace{2em}
}

DeclareDocumentCommandpreread{ m m }
{
    pdfbookmark[1]{Introduction}{intro}
    begin{tcolorbox}[width=textwidth]
        #1
        tcblower
        #2
    end{tcolorbox}
}

DeclareDocumentCommandnote{ o m }
{
% The original `cornell.cls` has these lines uncommented. They cut the
% space between fragments (`notes`).
%    IfNoValueT{#1} {
%        vspace{-1.5em}
%    }{}
    columnratio{.33}
    begin{paracol}{2}
        begin{leftcolumn}
            IfNoValueF{#1} {
                pdfbookmark[1]{#1}{note}
                begin{tcolorbox}[lowerbox=invisible,box align=top]
                    #1
                end{tcolorbox}
            }{}
        end{leftcolumn}
        begin{rightcolumn}
            begin{tcolorbox}[enhanced,lowerbox=invisible,box align=top,breakable] % <<< HERE I ADDED BREAKABLE
                #2
            end{tcolorbox}
        end{rightcolumn}
    end{paracol}
}
DeclareDocumentCommandsummary{ m }
{
    vfill
    pdfbookmark[1]{Summary}{summary}
    begin{tcolorbox}[
        enhanced,
        floatplacement=!b,
        float,
        colframe=black,
        colupper=black,
        opacitybacktitle=1,
        opacitytext=1,
        segmentation style={black!55,solid,opacity=0,line width=3pt},
        title=Summary,
        fonttitle=largebfseriessffamily]
        #1
    end{tcolorbox}
}

With previous class, the result looks like:

Second solution
In case that all left column boxes are like labels ore just a few words, it's also possible to forget the paracol package and use only a breakable and narrow tcolorbox with another box attached to the left.
The note command could be:
DeclareDocumentCommandnote{ o m }
{
%    IfNoValueT{#1} {
%        vspace{-1.5em}
%    }{}
    begin{tcolorbox}[enhanced, breakable,
        enlarge left by=.34textwidth, width=.66textwidth,
        overlay={
            IfNoValueF{#1} {
                pdfbookmark[1]{#1}{note}
                node[anchor=north west, outer sep=0pt, inner sep=0pt] at ([xshift=-.34textwidth]frame.north west) {begin{tcolorbox}[width=.325textwidth]#1end{tcolorbox}};
            }{}
        }
        ]
    #2
    end{tcolorbox}
}

Some adjustments have to be done to box sizes and interbox space but the result is quite similar:

Breaking tcolorboxes with parcolumns

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