In two-fds tcp, FIN/ACK, RST, timeouts and desire to stay as non-blocking as possible would still be a thing, so we’d have all the same functions and behaviors,

In two-fds tcp, FIN/ACK, RST, timeouts and desire to stay as non-blocking as possible would still be a thing, so we’d have all the same functions and behaviors, only SHUT_RD|WR parameters would go away. Pipes guarantee delivery if both sides agree, tcp doesn’t (but it tries hard asynchronously), that’s where the difference starts.