in the output. With mathdesigngm, I get (cropped output)

system          > tex > error on line 8 in file /tmp/test.tex: LuaTeX error  ...

 1    
 2     \usetypescriptfile[mathdesign]
 3    
 4     \usemodule[simplefonts]
 5    
 6     \setmainfont[Adobe Garamond Pro]
 7     \setmathfont[mathdesigngm]
 8 >> 
 9     \starttext
10     I want \m{x^2+y^2=z^2} in my text, and $\alpha\beta\gamma$ too.
11     \stoptext


\ctxcommand #1^^@-\directlua {commands.#1}
                                       
\font_helpers_low_level_define ...caledfontmode )}
                                                  \edef \somefontspec {at \n...
\font_helpers_trigger_define ..._identifier_class
                                                  \csname \v_font_identifier...
\font_helpers_set_math_family_a ...ily \endcsname
                                                  \else \font_helpers_set_ma...
\font_helpers_set_math_family_indeed ..._family_a
                                                  \scriptscriptfont #1\font ...
\font_helpers_set_math_family ...amily_indeed #1#2
                                                  \fi \else \font_helpers_se...
...
l.8