One cell. Each division halves the volume, so the whole stays egg-sized. One lineage keeps emitting, which makes an axis; every other cell reads the gradient where it sits. Fate is decided at division by what the cell reads, and the division axis follows the gradient, so the ball stops being a ball. Shape comes only from pushing apart, sticking together, and those readings.
Click a port, then another, to wire. Click a wire to change its weight or drop it.