CI on my fork can be ignored (I wonder if I can just turn it off).

In terms of progress, I'm half-way the handshake phase. Next step is implement Act 2 of the handshake, which should be a simple call to WriteMsgES of Sv2HandshakeState m_handshake_state; and updating the cipher like Sv2NoiseSession::ProcessMaybeHandshake does. The test harness can already write it, just needs to read it.

The next challenge is actual message parsing / serialising. The Transport abstract class converts between Span<const uint8_t> and CNetMessage / CSerializedNetMsg, while sv2_messages.h introduces Sv2NetMsg with its own serialisation. I'll have to study both in more detail to figure out if Sv2NetMsg can be made into a subclass of CNetMessage, or if there's another approach.

Finally, the Sv2TemplateProvider comes with its own SendBuf and GenerateWaitSockets. This has a lot of overlap with CConnman in net.h, but CConnman has too much p2p specific stuff to be used as a whole. I might therefore extract its socket handling code into another class.