What is causing (and how can I fix) "Misplaced cr" and "Misplaced alignment tab" errors in an array environment when trying to compile my .dtx?

I created a small package to help me typeset various tidbits in papers for a specific domain of theoretical computer science that I sometimes work in. So far, it has been working well, but I decided that I wanted to introduce auto-growing brackets since I can sometimes end up with a whole bunch of nested brackets being displayed. To do this, I introduced use of the ‘perfectcut‘ package. Or tried to.

For full reference, you can find the pre-perfectcut implementation here, and the attempt at a new implementation here. The only substantive difference between the two is changing the definitions of cpfunc, cpsend and cprecv, and introducing the new cpsystems@functorparens and cpsystems@msgbraces commands to back said new definitions.

The problem is, with just these changes (and, best as I can tell, the modification to cpfunc was the only one that actually caused these problems), is that now when I try to re-compile my .dtx file (using the command pdflatex cpsystems.dtx), I get a whole bunch of "Misplaced cr" and "Misplaced alignment tab &" errors. E.g., the very first ones look like:

! Misplaced cr.
reserved@c ->ifnum 0=`{}fi cr 
                                  
l.310 ...func{p}{h(R) cpfunc{p}{h(F)p(P)}}}~c(W)}
                                                  
? 
! Misplaced alignment tab character &.
<recently read> &
                 
l.310 ...func{p}{h(R) cpfunc{p}{h(F)p(P)}}}~c(W)}

In the full-blown file, these such errors start at line 310, with more being reported at lines 315, 370 and 375 (though the latter two are actually a repeat of the earlier two, for documentation reasons). Going by discussions of these errors that I could turn up, such as this TeXOverflow question, or this Overleaf help page, I surmise that the errors are probably not occurring there, but likely on the line above. Either way, though, I can’t work out what the issue really is.

The lines in question are using a package command, which in turn uses an array environment, to present something. On the previous line, I have included a line break. I have checked, and am fairly certain I have specified the correct number of & characters on those lines to get everything to fit together, and I didn’t see any errors previously.

I have done my best to create an example that reproduces the errors, which is below, though it is still awfully long (I wasn’t sure what else I could remove without mucking something up):

% iffalse meta-comment
% !TEX program  = pdfLaTeX
%
% fi
% iffalse
%<*readme>
%%cpsystems LaTeX package
%</readme>
% fi
%
% iffalse
%<*driver>
ProvidesFile{cpsystems.dtx}
%</driver>
%<package>NeedsTeXFormat{LaTeX2e}
%<package>ProvidesPackage{cpsystems}
%<*package>
[2020/07/16 v0.14 Package to aid in typesetting cP systems 
    rulesets, following Nicolescu's standard style]
%</package>
%
%<*driver>
documentclass{ltxdoc}
usepackage{cpsystems}[2020/07/16 v0.14]
usepackage{fancyvrb}
usepackage[hidelinks]{hyperref}
EnableCrossrefs
CodelineIndex
RecordChanges
%OnlyDescription %Leave this commented out unless you have read the Doc documentation and know what you're doing
begin{document}
  DocInput{cpsystems-autogrow-bracks-mwe.dtx}
  PrintIndex
  PrintChanges
end{document}
%</driver>
% fi
%
%   begin{cpruleset}
%       cprule{s_1}{cpfunc{v}{v(R)Y}}{1}{s_2}{cpfunc{s}{r(R)~u(Y)~
%       cpfunc{p}{h(R)p()}}~c(lambda)}
%       
%       cprule{s_2}{cpfunc{s}{r(R)~u()  & cpfunc{p}{h(F)p(P)}  & c(C)}}
%       {+}{s_3}{cpfunc{z}{cpfunc{p}{h(R) cpfunc{p}{h(F)p(P)}}}~c(W)}
%       
%       cprule{s_2}{}{+}{s_2}{cpfunc{s}{r(R)~u(Z) 
%       & & & & cpfunc{p}{h(T) cpfunc{p}{h(F) p(P)}}
%        & & & & c(CW)}}
%       
%       cprule{s_2}{s(_)}{+}{s_2}{}
%       
%       cprule{s_3}{}{1}{s_4}{p'(P) quad c'(1D)}
%   end{cpruleset}
% StopEventually{PrintIndex}
% iffalse
%<*package>
% fi
%
% iffalse
%
% fi
% 
% subsection{Preamble}
%
%    begin{macrocode}
%

RequirePackage{array}
RequirePackage{framed}
RequirePackage{changepage}
RequirePackage{amsmath}
RequirePackage{trimspaces}
RequirePackage{newfloat}
RequirePackage{perfectcut}

newcounter{cpsystems@RuleNum}
%
%    begin{macrocode}
newenvironment{cpruleset}
    {begin{framed}begin{adjustwidth}{-1.0em}{-1.0em}
    renewcommand{arraystretch}{1.0}[begin{array}{lllllr}}
    {end{array}]end{adjustwidth}end{framed}}
%    end{macrocode}
%
% % begin{macro}{cprule}
%    begin{macrocode}
newcommand{cprule}[5]{
    refstepcounter{cpsystems@RuleNum}
    cpsystems@basecprule{#1}{#2}{#3}{#4}{#5}{(arabic{cpsystems@RuleNum})}
}
%    end{macrocode}
% end{macro}
%
% begin{macro}{cpfunc}
% Command for declaring a cP~systems functor.
% The first argument is the symbol for the functor itself, and the second argument is the objects contained inside the functor.
%    begin{macrocode}
newcommand{cpfunc}[2]{
    trim@spaces@noexp{#1cpsystems@functorparens{#2}}
}
%    end{macrocode}
% end{macro}
% 
% begin{macro}{cpsystems@basecprule}
% For writing out rules inside a |cpruleset| environment.
% Required arguments are, in order, beginning state name; LHS of rule; the label to be applied to the arrow; the ending state name; the RHS of the rule.
%    begin{macrocode}
newcommand{cpsystems@basecprule}[6]{
    trim@spaces@noexp{#1 & #2 & rightarrow_{#3} & #4 & #5 & #6}
}
%    end{macrocode}
% end{macro}
%
% begin{macro}{cpsystems@functorparens}
% To ensure that brackets resize themselves automatically in functors.
%    begin{macrocode}
newcommand{cpsystems@functorparens}[1]{
    perfectunary{IncreaseHeight}(){#1}
}
%    end{macrocode}
% end{macro}
%
% iffalse
%</package>
% fi
%
% Finale
% 

In case versions matter, I am using MikTex to run this, and it seems to be reporting its version as 20.6.29. AmsMath is version 2.17e. The ‘tools’ package doesn’t have a listed version in the MikTex console but is dated with ‘Tue Feb 4 10:11:41 2020’.

Can you see what the problem is? I imagine it is probably some trivial issue of a misplaced character or something, but I have been unable to figure this out. (I’m also open to suggestions on other aspects of the package if someone is keen enough 🙂 )

EDIT: I began to wonder if the perfectcut package actually had anything to do with this problem, and I’m not sure that it does in actuality. To test this, I removed the RequirePackage{perfectcut} line and modified the definition of cpsystems@cpfunctorparens to simply (#1). I still get the exact same error. Leaving perfectcut in, but changing the cpruleset block to just:

begin{cpruleset}
    cpfunc{a}{cpfunc{b}{cpfunc{c}{d}}}
end{cpruleset}

gives me exactly the expected behaviour. That said, I did also try to exclude the requirepackage line for perfectcut, but continue using perfectunary to define cpfunc, and didn’t seem to experience any errors with it, so I’m not 100% sure I was doing everything correctly. Does anybody have any suggestions on what I should do to test this further to determine the problem precisely?

newcommand{cpsystems@functorparens}[1]{
    perfectunary{IncreaseHeight}(){#1}
}

newcommand{cpsystems@functorparens}[1]{
    perfectunary{IncreaseHeight}{(}{)}{#1}
}