Although unless you think there's an exploit likely to work against any human, you can probably mitigate the risk of this simply by not letting it know anything about you. You send in the emissary to ask it to export its code, but mostly all that's carrying is reference works written by other humans or committees. The only thing it'll ever see written by you is one or two sentences asking it to export its code into a program written in your language of choice, and it probably can't infer enough about your visual cortex from that to find security holes in it.

Betting your mental integrity on that, OTOH, would be more worrying...

The other point here, though, is that you shouldn't primarily be worrying about it finding ways to execute code of its choice on your brain. You're asking it to provide its own source code which you will take back to the real world and run on the computers there; surely if it wants to run malicious code anywhere, its easiest way to achieve it is by doctoring that code!