Do you know how much effort/time it would take to spin up a "play.kashmir", similar to "play.golang"? If it is minimal, it could be one of those items that really lowers the barrier to entry into the language.
Especially if you just do the compilation to Go and redirect the user to a prefilled play.golang.org page with the resulting code.
And a comment withe original code and a link back to your site :)
Pre-filling a page on another domain isn't possible unless the creator of that page explicitly creates a way to do it. That's an important security feature of web browsers.
You can create and run the entire snippet and redirect the user to the resulting page. "Prefilled" was a poor choice of words :(