So, yeah. Things are a bit dodgy in the level editor. Its a cool tool. But you have to know where to put things.
Click on the “Hero Placeholder” and look for the programmable Programmable in the Components. Check out this screenshot for exactly where.
The way they originally programmed the game from what I gather was to allow PC and NPC “Thangs” to be programmable. So you could actually enter code directly into a arrow towers code screen. Just like the heroes code screen.
Which opens an interesting conversation about adding programmable abilities to certain objects in the game and what that might add for game play. But this is no longer the “way” its being done so you would need to add that to your “help” section in the level if you added extra objects that could be programmed directly like the hero.