Well only sort of. As far as I understand, nothing about TCP means that ports can be reused, or that 0.0.0.0 has special meaning, or that processes can’t listen

Well only sort of. As far as I understand, nothing about TCP means that ports can be reused, or that 0.0.0.0 has special meaning, or that processes can’t listen on the same port, or IPv4 to IPv6 delivery etc. These are all operating system design choices, some of which stem from the sockets API. I’m pretty sure you could design a spec-compliant alternative which didn’t do any of these things, if you really wanted to.