You need to either enable write18 or add \runMPgraphicsfalse on the top of your file.
I put \runMPgraphicsfalse in the first line of test.tex. That changed nothing. Then i searched for write18 in the wiki. I found "ConTeXt defines \systemcommandmode that is 2 if \write18 is enabled, 1 otherwise. " on [1] so i wrote \systemcommandmode to get a 2 or 1 in textbody. [2] But i did not get a 1 or 2. Now i can see the circle and a "^" I have no idea, where the ^ comes from.
I think that this information needs to be added to the texlive installation page on the wiki.
in the year 2006 someone wrote [3]:
"""
Hans response on the mailing list
write 18 is a hack and pdfshellescape a sane replacement
in luatex it will probably be gone completely since there we have
\directlua 0 { os.execute("...") }
"""
I wonder if write18 is necessary 5 years later.
[1] http://wiki.contextgarden.net/write18
[2] https://github.com/jonasstein/context-quickstart/blob/master/test.tex#L2
[3] http://wiki.contextgarden.net/index.php?title=write18&direction=next&oldid=6802
--
Jonas Stein