If you dig into the RFCs, you'll see that ssh and telnet can negotiate whether each end can send/receive out-of-band messages about changes to window size. If they both can, the client side gets a local SIGWINCH, turns that into a notification over the wire, then the server side generates a SIGWINCH on its side that propagates through its pty and onto the programs attached to it.
For an rs-232 attached classic terminal that can change rows/columns, all you've really got is running eval `resize` and updating the environment variables. Most visual programs will check the environment variables on suspend/resume and maybe (it's been a while) on full-repaint (e.g. ^L on vim).
Upon further thought, the child can't inspect a parent's environment variables after forking, so my thinking of ^Z eval `resize`; fg can't be the way it worked. Maybe quit and restart vi was the only way back then. It's a been a while.
For an rs-232 attached classic terminal that can change rows/columns, all you've really got is running eval `resize` and updating the environment variables. Most visual programs will check the environment variables on suspend/resume and maybe (it's been a while) on full-repaint (e.g. ^L on vim).