Equivalent of \linegoal inside a tcolorbox raster?

Question

Is there an equivalent of \linegoal that would work with tcolorbox raster (I can use some luatex trickery if needed)?

In the following MnWE, \the\linegoal does not give correct results.

\RequirePackage{luatex85} % To fix linegoal (https://tex.stackexchange.com/a/525363/8425)
\documentclass[convert={size=640}]{standalone}
\usepackage[most]{tcolorbox}
\usepackage{linegoal}

\begin{document}
% Example adapted from tcolorbox documentation
\begin{tcbitemize}[raster equal height=rows,raster columns=3,
title=\thetcbrasternum,colframe=red!50!black,colback=red!10!white]
\tcbitem[colframe=blue!50!black,colback=blue!10!white,raster multicolumn=1]
\the\linegoal
\tcbitem \the\linegoal
\tcbitem \the\linegoal
\tcbitem[colframe=blue!50!black,colback=blue!10!white,raster multicolumn=2]
\the\linegoal
\tcbitem \the\linegoal
\tcbitem[colframe=blue!50!black,colback=blue!10!white,raster multicolumn=3]
\the\linegoal
\tcbitem \the\linegoal
\tcbitem[colframe=blue!50!black,colback=blue!10!white,raster multicolumn=2]
\the\linegoal
\end{tcbitemize}
\end{document}

Answer 1

linegoal assumes every line (including the possibly first line indentation per paragraph) starts from the left-most margin of text body of a page. Simple outer-most lines meet this condition, but not the lines in quote and tcolorbox environments, which are usually shifted to right.

I just added an answer to question How can I use \linegoal properly inside minipages?. OP's current question is just a special case of that one.

Applying new commands \markLineStart{<name>} and \getLineGoal{<name>} provided in the mentioned answer to OP's tcbitemize example:

\documentclass{article}
\usepackage{lipsum}
\usepackage[raster]{tcolorbox}
\usepackage{zref-abspos}

\makeatletter
\IfFormatAtLeastTF{2021-06-01}{% to use hook "para/begin"
  \newcounter{xlinegoal}
  \newcommand{\markLineStart}[1]{%
    \AddToHookNext{para/begin}{\zsaveposx{xlinegoal@#1}}%
    \ignorespaces
  }
  \newcommand{\getLineGoal}[2][\xlinegoal]{%
    \stepcounter{xlinegoal}%
    \zsaveposx{xlinegoal@#2@\the\c@xlinegoal}%
    \edef#1{\noexpand\dimexpr\the\dimexpr\linewidth+\zposx{xlinegoal@#2}sp-\zposx{xlinegoal@#2@\the\c@xlinegoal}sp\relax}%
    \ignorespaces
  }
}{\PackageError{xlinegoal}{LaTeX2e 2021-06-01 or newer is needed}{}}
\makeatother

% test helpers
\def\testXLineGoal{%
  X\hfill X
  
  \getLineGoal{tcb@\thetcolorboxnumber}
  \leavevmode\rlap{\the\xlinegoal}\rule{\xlinegoal}{.4pt}%
}

\begin{document}

% Example adapted from tcolorbox documentation
\begin{tcbitemize}[
  raster equal height=rows,
  raster columns=3,
  title=\thetcbrasternum,
  colframe=red!50!black,
  colback=red!10!white,
  before upper={\markLineStart{tcb@\thetcolorboxnumber}}
]
  \tcbitem[colframe=blue!50!black,colback=blue!10!white,raster multicolumn=1]
    \testXLineGoal
  \tcbitem \testXLineGoal
  \tcbitem \testXLineGoal
  \tcbitem[colframe=blue!50!black,colback=blue!10!white,raster multicolumn=2]
    \testXLineGoal
  \tcbitem \testXLineGoal
  \tcbitem[colframe=blue!50!black,colback=blue!10!white,raster multicolumn=3]
    \testXLineGoal
  \tcbitem \testXLineGoal
  \tcbitem[colframe=blue!50!black,colback=blue!10!white,raster multicolumn=2]
    \testXLineGoal
\end{tcbitemize}
\end{document}