If you're implementing NIP-09 deletion in a Nostr client, there's one check that's easy to miss: A kind 5 only counts when it's signed by the author of the event it targets. Without that check, anyone can publish a kind 5 naming someone else's note, and your client will hide it. You've built a censorship button and handed it to everyone. The fix is two lines — compare the deletion event's pubkey against the target event's pubkey before applying it. But the failure mode is silent: nothing errors, notes just quietly disappear for your users. Ran into this adding deletion to NostrComments. Ended up writing a test for it rather than trusting a careful reading.