Clustering and joining calls

From @mmcguinn:

> Sorry for the delay on this, but running through some of our normal callflow scenarios I have another potential concern. The flow goes something like this:
1.       CallA calls into an IVR menu
2.       CallA uses the IVR to place a call to B, which must first be confirmed by B before joining
3.       The IVR requests a call out to B (now CallB) and the IVR asks if B would like to accept the call.
4.       B says yes (or presses 1 or whathaveyou) and then CallA and CallB are joined.
 
> With a gateway arrangement my concern is that because CallB is not dialed with a join request (as it must interact with the IVR first) the gateway will be free to hand off the dial request to a different node than is handing callA. The join then becomes more difficult as it would require the two nodes to know about each other, and communicate in order to complete the join.
 
> Do you have any thoughts on to deal with this sort of issue? Perhaps an optional hint inside dial requests (similar to the existing join option in Rayo) specifically to request a gateway place the call on the same node as another call? Both these solutions leaving something to be desired in my mind, given that the goal of having such a gateway is to isolate clients and nodes from these sorts of concerns.