I prompted a tropical island – the hardest bugs were the ones where nothing was technically wrong

Opus 5.5 prompted a tropical island that runs in real time in the browser (PlayCanvas, WebGL/WebGPU), almost entirely by prompting an AI coding agent: water with refraction and caustics, a reef, sky, and a day–night cycle with real star positions. The code came fast. What took time were the bugs that don’t throw errors: * **Caustics looked fake even though they were computed correctly.** The light patterns on the floor came from a wave field with about twice the slope of the visible water surface. The floor was lit by a rougher sea than you could see. * **Avatars floated.** A shadow normal offset of 15 cm was tuned for an older engine version. The newer one applies it in full, so every contact shadow started about 30 cm from its caster. * **A realistic night is unusable.** A moonless night is about 1000× darker than day, which on screen is just black. I had to add a fake “moonlight” term. * **AI self-review loops go in circles.** An automated “make it more photoreal” loop mostly…