{
  "name": "water_flows_sideways",
  "description": "Water on a flat surface should spread horizontally",
  "seed": 42,
  "init_mode": "empty",
  "setup": [
    {"type": "fill_rect", "x": 100, "y": 110, "w": 20, "h": 1, "material": "stone"},
    {"type": "set_cell", "x": 105, "y": 108, "material": "water"},
    {"type": "set_cell", "x": 105, "y": 109, "material": "water"}
  ],
  "steps": 30,
  "assertions": [
    {"type": "material_count_in_region", "x": 110, "y": 108, "w": 5, "h": 3, "material": "water", "min": 1, "max": 10}
  ]
}