Dead cells as reaction mass, using standard cell drive system. Variable but limited Isp. The probe rearranges to form a microwave antenna. A salvo of probes rendezvous in flight. New software is continuously broadcast.
Intercloud dust grains.
Thousands of probes are launched in rapid succession. Periodic rendezvous, form new point probes from damaged cells. Interrogator cells move up and down the line to determine damage. Treat dust grains as blobs of free charge passing through cell. Cells are arranged in lines perpendicular to the velocity.