Signal, a five-minute toy at signal.html: you are a point of light in a dark grid, signals pulse around you, and dragging a line from one to you sends packets of light along it that make you grow. Ideas arrive one at a time once the last is used: a line's capacity (a bright signal backs up until it has two lines), two colours merged at a node into a packet worth much more, reach (far signals need a relay node), and a red pulse to tap before it eats a line. A ghost hand and a one-line hint show the move only when the player is stuck. Rules in src/signal/rules.ts with tests, SIGNAL.md has the stages and numbers, an e2e test drags a line on desktop and phone master