> The recipient has registered their address and private view key with a watcher. The view key lets it see incoming payments; it can never spend them.

Noooo, Monero tips should allow the recipient to easily maintain privacy.

An alternative approach is for the sender's client to publish an event with the transaction details. The recipient (or a watcher) can then sign the tip event.

I'm sure Monero wallets would also gladly implement support to give the transaction data back to the nostr app through a nostr URI so people don't have to manually copy transaction details.