@paweljakubas how address derivation would help here 🤔?

I was wondering if using for example first account public key ( ::Key 'AccountK XPub) as unique wallet identifier is not ok here (instead of PrimaryKey)..

It could be okay. And we might choose that. Though, requiring this as a key for the DB layer would be introducing needless coupling and a bit of confusion I believe. Plus, we will need to define some serialization instances on the key probably, or have a way to transform it to a suitable format for the underlying DB engine. Doing that on a Key 'AccountK XPub would require us to define the corresponding instances in the Cardano.Wallet.AddressDerivation module which doesn't make sense (or have an orphan instance which is also, not desirable). Instead, we need here a new type from for the db layer and, we'll have a way to generate such key from a wallet; this way might be by using the public key of the first account, but that's a decision which lives outside of the DB layer.

@KtorZ thanks for the answer! Makes sense, especially the coming demand for serialization instances when DBLayer will adopt Serialization constraint