Increment-2 mechanism — animated over 60 updates (patch 0.3 mm, seed 17)
Increment 2
infected cells (60 updates)
9 → 16
locality ratio (< 0.75 = local)
0.61
virus diffusion length
25 sites
Play it. The virus field (blue) diffuses from the seeded lesion; healthy cells (●) turn infected (●) stochastically where the field is strong. New infections land a mean 15.01 sites from a prior-infected cell — 0.61× the 24.6-site uniform-random null (a shuffled-field control gives 1.13), so spread is genuinely local. Mechanism only — no resistance/IFN or death yet.