Hey guys, sorry for a late response; I've been busy lately.
So I finally figured out how to import assets, and I've promptly imported the small key scripts, but I couldn't find the .png files OR the sprite files for those various items in the Children of Solarus github. I therefore found third-hand pngs and dropped those into their proper file destination. Upon doing so, I booted the quest editor to go and press the "Add to quest" button, but when I right clicked on each png, there wasn't one. I booted the quest, and I got the same error message:
Error: In create_door: bad argument #1 to ? (Bad field 'opening_condition' (equipment item 'dungeons/small_key' is not saved))
What might be going wrong now that I've imported those scripts?
IMPORTANT ADDENDUM: I've tested one of locked doors by setting their unlock condition to rupees instead of keys, and I get the very same error message, except with rupees not being saved instead of small keys. Given this, I think that it'd be more important for me to learn how to get my quest to save the states of these items. I've double-checked both scripts, and I found the line
item:on_obtaining(variant, savegame_variable)
in both. Is this supposed to save the items?