How do light clients using compact block filters get relevant unconfirmed transactions?
There's no design consideration in Neutrino / BIP157 for unconfirmed transactions, but it's not as much of a concession with context. A light wallet can effectively do nothing with information about an unconfirmed transaction as they can not verify anything about its validity to begin with. At best it is a suggestion that a transaction may have occurred, but this is even weaker than a normal unconfirmed transaction sent to a fully validating wallet.
It has always been an issue with &quot;SPV&quot; wallets that they can be duped into showing completely absurd false data, for BIP37 especially it was completely possible to sniff the incoming filter and dynamically produce transactions paying to the addresses that likely matched it billions of dollars. The client, as dumb as it is, can only show them to the user and hope that common sense on the part of the user prevails.