make @safe "non-escapable"?

[Robert]

The purpose of my proposal was to be able to sandbox code. It is quite
different, whether you allow the sandboxed code calling a trusted
function, you declared or allowing the sandboxed code to declare a
trusted function, which would simply break the sandbox.
On Thu, 2013-02-07 at 01:07 +0100, Era Scarecrow wrote:
> True, but if you have one or two functions that break @safe but 
> you know are safe, then you need to override it. Otherwise you 
> have extra hoops to go through. If @safe code can't call @trusted 
> code, then this is a non-issue (as it's just another step/tier 
> towards safe).