Fallback characters with combofont for teletype font?

I’m trying to find a solution for https://stackoverflow.com/questions/65177985/pandoc-markdown-to-pdf-fixing-missing-character-warnings ; and for that, I found:

• Inserting _any_ unicode character in Latex document
• Adding headers and footers using Pandoc

… and I almost got there with combofont; here is an MWE, with the headers output from pandoc:

tester.tex:

(EDIT: look in the history to see the original output from pandoc – I’ve cut off most of the preamble stuff, and it seems the below MWE reproduces the same problem):

documentclass[]{article}
usepackage{lmodern}
usepackage{combofont}
setupcombofont{multiscript-regular}
{
  {file:lmroman10-regular.otf:combodefaultfeat} at #1pt, % have this in C:/Windows/Fonts/lmroman10-regular.otf ; C:/bin/texlive/2020/texmf-dist/fonts/opentype/public/lm/lmroman10-regular.otf
  {file:DejaVuSerif.ttf} at #1pt % have this in C:/Windows/Fonts/DejaVuSerif.ttf ; C:/msys64/mingw64/share/fonts/TTF/DejaVuSerif.ttf ;
}
{
   {},
   fallback
}
DeclareFontFamily{TU}{multiscript}{}
DeclareFontShape {TU}{multiscript}{m}{n} {<->combo*multiscript-regular}{}
%renewcommandttdefault{multiscript} % TEX.SE 514940
AtBeginDocument{fontfamily{multiscript}selectfont} % have to do it this way; if the ...selectfont is just in the header, then begin{document} resets it, so then we'd have to write the ...selectfont in the body of the document explicitly, which we'd rather not do

author{}
date{}

begin{document}

Here is a test of a glyph that otherwise trips up *latex: ┌

%begin{verbatim}
%Here is a test of the same glyph inside verbatim: ┌ ...
%end{verbatim}

end{document}

Compiling this:

$ lualatex -halt-on-error -interaction=batchmode tester.tex
This is LuaHBTeX, Version 1.12.0 (TeX Live 2020/W32TeX)
 restricted system commands enabled.

luaotfload | loaders : eval: found tfmdata for "luaotfload<1>", injecting.

$ grep 'Missing character' tester.log

… and the PDF result is:

So, for normal/roman/upright text, the glyph is successfully replaced, and there are no ‘Missing character’ messages in log.

---

Now, if you uncomment the {verbatim} snippet in the tester.tex, the compilation result is:

$ lualatex -halt-on-error -interaction=batchmode tester.tex
This is LuaHBTeX, Version 1.12.0 (TeX Live 2020/W32TeX)
 restricted system commands enabled.

luaotfload | loaders : eval: found tfmdata for "luaotfload<1>", injecting.

$ grep 'Missing character' tester.log
Missing character: There is no ┌ (U+250C) in font [lmmono10-regular]:!

… and the resulting PDF is:

So, the character did get replaced in normal text and font – but did not get replaced in the {verbatim} environment text, where teletype font is used (and a corresponding "Missing character" is output in log).

---

My question is: how can I set up combofont, so I can provide a character fallback, for everywhere a teletype font is used (verbatim and lstlisting environments, etc)?

(as a note, I was originally interested to provide fallback glyphs only for the teletype text/font; the only reason I provide a fallback for the normal text/font in the above MWE, is because that is the only thing I could get working so far – so at least it is a good starting point).

---

EDIT: Found a work-around here: Define fallback font for missing glyphs in LuaLaTeX – seemingly, all I was missing was a renewcommandttdefault{multiscript} after the DeclareFontShape command. This does work, and produces this in PDF:

… however, then this uses DejaVuSerif.ttf as fallback for the teletype font – so I do not get a teletype/mono font shown at all; but what I’d like is to use DejaVuSerif.ttf as fallback for normal/upright/roman text – and use DejaVuSansMono.ttf as fallback for teletype text; how can I do that?