That is actually a very practical solution. If I understand it correctly the client does not need to trust every relay to honor NIP 09. It can fetch my own kind 5 deletion events together with my kind 7 reactions and locally ignore any reaction whose event id is referenced by a newer deletion. That sounds like it would solve exactly what I saw in Nostrich. The relay may still serve the old reaction but the client already knows that I deleted it and does not have to show it again. I also like that this only needs to be trusted for my own events. I think this is worth testing against the relays that kept bringing the reaction back. I might even log which relays honor the deletion and which ones keep serving the old event. Thanks for giving a concrete implementation instead of only explaining why the problem happens.