How to span brackets on some rows in longtable?

Question

The goal is to place a brackets into the table (longtable) to embrace some rows of this table:

The solution which involves rdelim and \multirows command (described here: usage of \rdelim) gives not uniform bracket widths as well as not uniform bracket line widths while distinct brackets have various span: \rdelim example

So the natural solution of the problem is usage of putting "remembered pictures" into the table and spanning brackets that are "decorations": decorations in \longtable

But the problem is that the nodes can travel to the next page:

What to do, to prevent nodes against escaping to the next page?

The solution given for mathematical formulas (forcing nodes to not travel to the next page) does not work here.

MWE:

\documentclass[12pt,a5paper,twoside]{article}
\usepackage[polish]{babel}
\usepackage{booktabs}
\usepackage{longtable}
\usepackage{tikz}
\usepackage[a5paper]{geometry}
\usetikzlibrary{decorations.pathreplacing}

\begin{document}
\begin{longtable}{p{3cm}p{3cm}}
    \toprule
    first column & second column\tikz [remember picture] \node (rightmark) {};\\
    \midrule
    \endhead
    A & A \\
    A & A \\
    A & A \\
    A & A \\
    A & A \\
    A & A \\
    A & A \\
    A & A \\
    A & A \\
    B & B \tikz [remember picture] \node (n1) {};\\*
    B & B \\*
    B & B \\*
    B & B \\*
    B & B \\*
    B & B \\*
    B & B \\*
    B & B \\*
    B & B \\*
    B & B \\*
    B & B \\*
    B & B \tikz [remember picture] \node (n2) {};\\
    C & C \\
    C & C \\
    C & C \\
    C & C \\
    C & C \\
    C & C \\
    C & C \\
    C & C \\
    C & C \\
    C & C \\
    C & C \\
    C & C \\
    \bottomrule
\end{longtable}
% curly brace
\tikz [overlay,remember picture]
      \draw [decoration={brace,amplitude=2mm},decorate,thick]
      (n1.north -| rightmark) -- (n2.south -| rightmark)
      node [midway,right=4mm,align=left] {The bracket\\spanned on\\some rows};
\end{document}

Answer 1

The solution given in the question you linked (How can I keep my TikZ overlay picture on the same page?) does work here, in the following sense:

\begin{longtable}{p{3cm}p{3cm}}
    \toprule
    first column & second column\tikz [remember picture] \node (rightmark) {};\\
    \midrule
    \endhead
    A & A \\
    A & A \\
    A & A \\
    A & A \\
    A & A \\
    A & A \\
    A & A \\
    A & A \\
    A & A \\
    B & B \tikz [remember picture] \node (n1) {};\\*
    B & B \\*
    B & B \\*
    B & B \\*
    B & B \\*
    B & B \\*
    B & B \\*
    B & B \\*
    B & B \\*
    B & B \\*
    B & B \\*
    B & B \tikz [remember picture] \node (n2) {};%
    \tikz [overlay,remember picture]
      \draw [decoration={brace,amplitude=2mm},decorate,thick]
      (n1.north -| rightmark) -- (n2.south -| rightmark)
      node [midway,right=4mm,align=left] {The bracket\\spanned on\\some rows};\\
    C & C \\
    C & C \\
    C & C \\
    C & C \\
    C & C \\
    C & C \\
    C & C \\
    C & C \\
    C & C \\
    C & C \\
    C & C \\
    C & C \\
    \bottomrule
\end{longtable}%

Note the % after the draw command; otherwise the first entry C will be shifted to the right. Clearly, this solution only works as long as both nodes are on the same page.

Otherwise, you would have to look at the answer of the question Tikz - How to overlay Decorations over longtable that you linked already.