Yeah I understand that if someone generates a key then burns it, there's no way to know. But it was shocking for me to realize that there doesn't seem to be a universal mechanism to ensure you are sending something to *the correct blockchain*. The sender should know what chain their coins are on, so if the recipient embeds that metadata in the address or QR code, some basic validation should be possible.

In L2 it seems like a "handshake" should be possible as well. Eg Where the sender sends in infinitesimal amount of coins, and the recipient moves the funds in a way the sender can see, so the sender knows the funds sent were accessible.

Huh interesting idea.

You could probably build something like this on Solana or the EVM directly. The thing is, if you get the address of the recipient wrong, how can you tell? Like if I send SOL to a payee, then I can look at the chain to make sure that SOL was sent from my address to the payee's address. But that doesn't change the fact that I don't know if the payee is who I think it is.

Are you thinking about situations where, say, you meet in person, then send an amount and have the recipient verify they received an amount, then send the rest? Like a multi-party escrow?

Third-party escrow contracts are very common.