[Workaround found] CodeIgniter 3.0 cannot access native $_SESSION

It is the same session, just with a few more variables set in it by CI - and yes, that makes it very hard to share a session between two applications.

That's an unintentional consequence, but you should never do it anyway.

I see that CI Session have it's own session handler. So, the only way to use CI Session outside CI is by using the same session handler.
However, I think that will be very difficult. So, I'm now using encrypted cookie instead.