Evolution of a typical simulation from the 20flat suite, which includes a migration trap at 1 au. Embryos accrete from a ring (top left panel) and grow until they saturate the corotation torque (top right, zero torque locations in gray), then migrate inwards in resonant convoys. At the end of the disk phase (bottom left), there is an inner resonant chain and an outer, less massive, and more compact one. By the end of the simulation (bottom right), the system has experienced a dynamical instability, breaking the resonances and merging planets.