One more thing: we need test coverage for "suspend on full queue, resume when the logjam clears". qmp-test.c got the building blocks. Something like this:
send_cmd_that_blocks() eight times
send_oob_cmd_that_fails()
unblock_blocked_cmd()
recv_cmd_id() for the 1st in-band command
recv_cmd_id() for the oob command
unblock_blocked_cmd()
recv_cmd_id() for the 2nd in-band command
... repeat for the remaining six in-band commands ...
