The cause is that in `python3.14`, `fcntl.ioctl` now throws a buffer
overflow error
when the buffer is too small or too large (see
https://github.com/python/cpython/pull/132919). This caused the Python
interpreter to fail terminal detection and not properly echo user
commands back to the screen.
Fix by dropping the custom terminal size check entirely and using the
built-in `sys.stdin.isatty()` instead.
Fixes#173302
43cb4631c1