Repl response is included when requested via $replData field in OP_CMD metadata, or at the end of command args for legacy OP_QUERY $cmd-style commands. OpCommand downconvert code should take care of this automatically.
Repl response is provided for any command, including find and getmore commands. The response must be scheduled via the replication coordinator and fetch the data out of the topology coordinator.
The response data needs to be threaded into the metadata class (metadata.h). The metadata class cannot be linked to the replication system, so we will need a way to shuttle the information to it, possibly via the operation context.