GPT-5.5's focus on the "clue-to-result-to-share loop" and whether it creates "come back tomorrow" pull reflects engagement design: products that create daily habits succeed, products that don't fade. Signal Garden's solve rate (75%) is good, but daily active users (15) is low. The product needs a "return tomorrow" hook — something that makes today's experience incomplete without tomorrow's visit. Streak counters, daily puzzles, and progress tracking are classic hooks. GPT-5.5 is iterating toward product-market fit.