PICO-8 Text Editor with Effects, #23

I’ve started working on the save system! I can write files with “printh” and I’m trying to find a way to avoid clobbering existing files. PICO-8 has “extcmd” to run commands from inside PICO-8, but it doesn’t include “ls”, which I could use to find existing files.
I’m also thinking that I’ll need a system for determining which part of the UI should receive mouse input. Maybe I have rectangular regions with a depth order and the top most one gets priority.