Every walker is ignorant.
A walker launches from the dashed outer ring and chooses north, south, east, or west with equal probability. If it escapes the kill ring, another is released. There is no tip-seeking force in the rule.
The structural reveal
Exposure compounds itself.
This is a lattice model of diffusion-limited aggregation, the same family of rule that makes branching forms from electrodeposition to idealized dielectric breakdown—not a literal lightning forecast.
The boundary is not equally reachable.
The blue ghost field repeats that same walk without adding material. Its attachment histogram estimates harmonic measure: the probability distribution of first arrival over this exact boundary. A hollow demands a rare sequence through its mouth; a tip intercepts paths from many directions.
One hit changes the next weather.
An attachment extends an exposed region, which usually makes it still easier to reach. The forecast is recomputed after every visible strike. Branches screen the space behind them, so chance at the particle scale becomes persistent preference at the shape scale.
Probe rule: 480 successful non-growing arrivals from the current launch ring. Walkers crossing the outer kill ring or reaching the finite step cap are discarded and relaunched. “Zero observed” means below this finite sample's resolution, never mathematical impossibility. Shield editing is restricted to adjacent cells before the first attachment so the conductor remains connected.