> To remain useful as border router, the replace-by-fee patched core should
> only relay double spend if it actually replaces an earlier transaction, as
> otherwise the replace logic that is according to your commit more than just
> fee comparison, would have to be replicated in the proprietary stack and
> mempool might get out of sync with that of the border router.
>

Why don't you use getrawmempool RPC call to synchronize mempool contents?