whatA planet, a ring of massless particles, and two tiny moons riding circular orbits inside the ring. The particles feel the planet, both moons, and a crude declared stand-in for the ring's collisional cooling -- a gentle relaxation toward the local circular flow, because real rings jostle themselves calm.

whyThe claim: the lanes are swept, not carved. A moon repels ring material from its own orbit -- every passage hands nearby particles a little eccentricity, cooling settles them a step farther away, and within tens of orbits each moon rides in a clean swept lane with sharpened edges, while spiral moonlet wakes corrugate the material downstream (the same wakes Pan drags through the Encke gap). Make the moons massless and the lanes never appear -- the control is one URL parameter away.

howKick-drift-kick leapfrog; the moons are kinematic circles (their masses are ring-moon scale, declared at 1.2e-5). The HUD reports each lane's density against its flanks and the confined fraction. Drag a moon radially: it keeps its longitude, takes the new orbit, the old lane heals and a new one opens. One integer seeds the ring.