Hello Chris,
rtpengine_manage() is just a wrapper that makes context-sensitive invocations of rtpengine_offer() and rtpengine_answer(), so that you don't have to choose which of them to call manually. But it's not perfect.
There are nevertheless situations where this manual use of the offer/answer functions is necessary, and it sounds like this is one of them.
There is a larger question of whether rtpengine_manage() should support PRACK; it seems like the answer is yes. But this lacking cannot be framed as "RTPEngine doesn't support PRACK" or anything like that. RTPEngine can support any SDP-bearing request and reply, since RTPEngine does not care about SIP semantics per se.
-- Alex