Point A sounds perfect to me. Why bother with GET at all?
For point B, I notice that I get an "x-requested-with: XMLHttpRequest" when doing ajax() from inside jQuery. I assume this is not there when someone SCRIPT SRCs something (why would it be?), so that may be useful to someone.
For point B, I notice that I get an "x-requested-with: XMLHttpRequest" when doing ajax() from inside jQuery. I assume this is not there when someone SCRIPT SRCs something (why would it be?), so that may be useful to someone.