I have succeeded getting a minimalist connection between my Mac and my Raspberry Pi (RPi). With one USB-Serial adapter cable, I login to my RPi and do command-line work, even using Vim to edit files, and therein is my problem. I have defined my login process to use xterm-256color as the terminal type, and I can get that behavior on my Mac by either using the "screen" command or by running Z-Term. However, in both of those cases, as soon as I run either Vim or nano on the RPi, my terminal emulator on the Mac is now locked into 80x24, no matter the size of the actual window (again, the same behavior occurs in both Z-term and the "screen" command. Even after the Vim or nano session is exited, the terminal emulator is now locked into 80x24 behavior.
Has anyone any well-informed idea of what is happening, and how I can get the normal behavior of xterm-256color? And just to be clear, the normal behavior is what I get when I SSH into RPi in a full network configuration: a resizable terminal, the full size of which is dynamically detected by Vim.