dr-test | Test helps you to generate random test data | Serialization library

Edit: You seem to assume that the the handshake from gocardano/go-cardano-client and the one described in node.proto somehow are related to the same implementation. Actually, I don't think they do.

The TCP-based handshake follows the Shelley protocol specs and sends a payload with the encoded versionTable. The gRPC-based HandshakeRequest instead is, as you also considered, just a nonce. There's nothing in the proto schema that hints to the Shelley protocol. The comments on the Nonce field also say that quite explicitly: "Nonce for the server to authenticate its node ID with."

So it would be a bit strange to assume that this nonce and the versionTable payload have anything in common at all.

Edit 2: In addition, it seems the "Jormungandr" rust node implementation does not support Shelley at all, so when you say you can't connect to the nodes in the relay topology, I think you shouldn't look for answers in the Jormungandr repository. Instead, I think the relays run the Haskell implementations of the Ouroboros network.

Now as for why you can't connect, the go-cardano client panics on some unchecked type assertions, because after the QueryTip Shelley message chainSyncBlocks.RequestNext, the relay servers respond with a different mini-protocol altogether, transactionSubmission.msgRequestTxIds as shown by running the client with TCP and tracing the messages: