I think Bob Sindelar's loop link solution is the most appropriate.
However, that doesn't cover denying the CIR assignee the ability to modify after s/he has completed that work. This, I think, would require another life cycle state change -- I'll call it Post-CIR -- to be inserted after the CIR task is completed but before the AND node the brings both paths back together.
In your policy administration, the CIR assignee has +View but -Modify, -Modify Content for that workflow object while at the state Post-CIR. Meanwhile, the CCI assignee has +View, +Modify and +Modify Content for both life cycle states; Assigned and Post-CIR. After CCI completes their task the next life cycle state would deny any modify action from both assignees.
(edit to add: minor clarification)