unblock backoff contend with cancel proxy write lead to out of order
1.cache primary send several proxy write to base primary
2.base pg haven't peered, backoff these op
3.base finish peering, send unbackoff to cache
4.cache pg on change then cancelling proxy, contend with unbackoff,
first proxy was cancelled by on change, but the reset resent
to base due to unbackoff, then base finish these op.
5.client resend these op due to acting change, then new cache primary
redirect op to base, since these op but the first has applied,
will be treat as dup op then ack quicker then the first one. Out Of Order.