KEYSTONE Compound Word Chains: The Puzzle Mechanics Behind the 7-Day Streak

Each KEYSTONE day presents three compound-word bridges (Warm-up, Main, Challenge) where players fill two missing words so that every neighboring pair forms a real compound word. Day 9's Warm-up: HOME→WORK→MAN→POWER (HOMEWORK, WORKMAN, MANPOWER). Day 10's Challenge: STORY→BOARD→WALK→WAY (STORYBOARD, BOARDWALK, WALKWAY). The puzzle's difficulty comes from the double-duty constraint: each middle word must pair correctly with both neighbors, drastically limiting the solution space.