Working but slow

backend/test/caEngines.test.ts

@@ -188,6 +188,35 @@ describe('CA engine runtimes', () => {
     expect(stepped.cells).toEqual(cells(5, 5, [[0, 2]]))
   })
 
+  it('uses simulation rng_seed to choose deterministic Naga heads', () => {
+    const current = cells(6, 6)
+    const baseParams = {
+      caClass: { dimensions: 3, states: 7 },
+      renderer: { id: 'voxel-3d' },
+      simulation: {
+        engineId: 'naga-3d',
+        ruleId: 'naga-3d',
+        grid: { size: [6, 6, 6], boundary: 'wrap' },
+        initialCondition: {
+          type: 'cells',
+          cells: [[1, 2, 2, 1], [4, 2, 2, 1]]
+        }
+      }
+    } satisfies SceneParams
+
+    const leftSeed = stepCaSimulation(current, settings({
+      ...baseParams,
+      simulation: { ...baseParams.simulation, rng_seed: 'bar' }
+    }))
+    const rightSeed = stepCaSimulation(current, settings({
+      ...baseParams,
+      simulation: { ...baseParams.simulation, rng_seed: 'alpha' }
+    }))
+
+    expect(leftSeed.settings.simulation?.initialCondition?.cells).toEqual([[4, 2, 2, 1], [0, 2, 2, 1]])
+    expect(rightSeed.settings.simulation?.initialCondition?.cells).toEqual([[1, 2, 2, 1], [3, 2, 2, 1]])
+  })
+
   it('keeps Naga 3D sparse coordinates in place when fixed boundaries would leave the grid', () => {
     const current = cells(5, 5)
     const params = settings({