Question How do you access an AsyncGPUReadbackRequest from a job? (unsafe pointer issues)

I am trying to go through 5M pixels of a 3D texture in a job. The 3D texture is held in a compute buffer.
This code isn't allowed by the safety system and causes problems.
I could loop through each z in the main thread and pushing a NativeArray<ushort> to the job but this is slow. Is there another way?

Code (CSharp):

1. using com.zibra.liquid.Solver;
2. using Drawing;
3. using Fraktalia.VoxelGen;
4. using Unity.Burst;
5. using Unity.Collections;
6. using Unity.Collections.LowLevel.Unsafe;
7. using Unity.Jobs;
8. using UnityEngine;
9. using UnityEngine.Rendering;
10.  
11. public class ZibraLiquidGridReadback : MonoBehaviour
12. {
13.     public                              ZibraLiquid             liquid;
14.     public                              VoxelGenerator          voxel;
15.     [NativeDisableUnsafePtrRestriction] AsyncGPUReadbackRequest newRequest, oldRequest;
16.     bool                                                        initialized;
17.     public bool                                                 drawGizmos;
18.     public float                                                threshold = 0.01f;
19.     public int                                                  step      = 2;
20.  
21.     //capture liquid's density textyre
22.     void Update()
23.     {
24.         if (liquid.DensityTexture == null) return;
25.         if (!initialized)
26.         {
27.             newRequest  = AsyncGPUReadback.Request(liquid.DensityTexture);
28.             initialized = true;
29.         }
30.         newRequest.Update();
31.         var gridSize                        = liquid.GridSize;
32.         if (newRequest.hasError) newRequest = AsyncGPUReadback.Request(liquid.DensityTexture);
33.         if (newRequest.done)
34.         {
35.             oldRequest = newRequest;
36.             newRequest = AsyncGPUReadback.Request(liquid.DensityTexture);
37.         }
38.         JobLauncher();
39.     }
40.  
41.     [BurstCompile]
42.     public struct DrawJob : IJobParallelFor
43.     {
44.         [ReadOnly] public Vector3    edge;
45.         [ReadOnly] public Vector3Int gridSize;
46.         [ReadOnly] public int        step;
47.         [ReadOnly] public float      threshold;
48.         [ReadOnly] public float      nodeSize;
49.         [ReadOnly] [NativeDisableUnsafePtrRestriction]
50.         public AsyncGPUReadbackRequest oldRequest;
51.         public CommandBuilder builder;
52.  
53.         public void Execute(int z)
54.         {
55.             var data = oldRequest.GetData<ushort>(z);
56.             using (builder.WithDuration(.2f))
57.             {
58.                 for (var x = 0; x < gridSize.x; x += step)
59.                 {
60.                     for (var y = 0; y < gridSize.y; y += step) ExtractDensities(z, x, y, data);
61.                 }
62.             }
63.         }
64.  
65.         void ExtractDensities(int z, int x, int y, NativeArray<ushort> data)
66.         {
67.             var flatIndex = 4 * (x + y * gridSize.x);
68.             var density   = Mathf.HalfToFloat(data[flatIndex + 3]);
69.             if (density > threshold)
70.             {
71.                 var material1 = Mathf.HalfToFloat(data[flatIndex]);
72.                 var material2 = Mathf.HalfToFloat(data[flatIndex + 1]);
73.                 var material3 = Mathf.HalfToFloat(data[flatIndex + 2]);
74.                 var material0 = density - material1 - material2 - material3;
75.                 var color     = new Color(material1, material2, material3);
76.                 builder.WireBox(edge + nodeSize * new Vector3(x, y, z), nodeSize * new Vector3(1f, 1f, 1f) * step, color);
77.             }
78.         }
79.     }
80.  
81.     void JobLauncher()
82.     {
83.         if (!drawGizmos || !initialized || oldRequest.hasError || !oldRequest.done) return;
84.         var edge     = transform.position - liquid.ContainerSize / 2.0f;
85.         var gridSize = liquid.GridSize;
86.         var builder  = DrawingManager.GetBuilder(true);
87.         builder.Preallocate(gridSize.x * gridSize.y * gridSize.z * 4);
88.         var drawJob = new DrawJob
89.         {
90.             oldRequest = oldRequest, edge = edge, gridSize = gridSize, step = step, threshold = threshold, nodeSize = liquid.NodeSize,
91.             builder    = builder
92.         };
93.         var jobHandle = drawJob.Schedule(gridSize.z / step, 8);
94.         jobHandle.Complete();
95.         builder.Dispose();
96.     }
97. }