review beg for #19455 (which arguably should have been in the last release with -generate to make multiple bitcoin command line tutorials work again for users), as requested by ajonas and MarcoFalke. It's a quick review with complete test coverage.
certainly is difficult (i imagine) to distinguish between "this is a really clean PR and I really have no comments on it, it's RFM" and "I've done my best but I'm not familiar enough with bitcoin to really review this"
adiabat: i think the reason not to do other ports was to prevent bitcoin nodes being used as a primitive botnet that'll start connecting to arbitrary services (or to be mistaken for being part of a botnet if someone spams military.gov's rsh port as a thing to connect to for bitcoin p2p maybe. never been able to judge if that makes much sense these days
sdaftuar: do you know whether there are nodes that disconnect on unknown message types? Bitcoin Core just drops them (which I think is the only sensible behaviour)
sdaftuar: I think that's good it was unclear between matt and I on bip339 implemn in rust-bitcoin about why 339 bumps both protocol version and wtxid-relay
however, i think we need to make sure software on the network knows to ignore unknown messages pre-verack to make this a possibility. bitcoin core historically has disallowed unknown messages pre-verack