feat(world-gen): implement worm cave pass in CaveCarver

VoxelEngine.Tests/WorldGen/CaveCarverTests.cs

@@ -115,4 +115,72 @@ public class CaveCarverTests
         Assert.True(airAtSeamC1 > 0, "c1 seam column had no air — carve too sparse?");
         Assert.True(airAtSeamC2 > 0, "c2 seam column had no air — carve too sparse?");
     }
+
+    [Fact]
+    public void WormCaves_IsDeterministic_ForSameSeedAndChunkPos()
+    {
+        var c1 = new CaveCarver(seed: 999, Blocks, Cfg);
+        var c2 = new CaveCarver(seed: 999, Blocks, Cfg);
+        Chunk a = MakeStoneChunk();
+        Chunk b = MakeStoneChunk();
+
+        c1.CarveWormCaves(a, new Vector3i(0, 4, 0));
+        c2.CarveWormCaves(b, new Vector3i(0, 4, 0));
+
+        for (int x = 0; x < Chunk.Size; x++)
+        for (int y = 0; y < Chunk.Size; y++)
+        for (int z = 0; z < Chunk.Size; z++)
+            Assert.Equal(a[x, y, z], b[x, y, z]);
+    }
+
+    [Fact]
+    public void WormCaves_OnlyConvertsSolidToAir_NeverWater()
+    {
+        var carver = new CaveCarver(seed: 999, Blocks, Cfg);
+        Chunk c = MakeStoneChunk();
+        // Set every voxel along a diagonal to water — must survive.
+        for (int i = 0; i < Chunk.Size; i++)
+            c[i, i, i] = Blocks.Water.Id;
+
+        carver.CarveWormCaves(c, new Vector3i(0, 4, 0));
+
+        for (int i = 0; i < Chunk.Size; i++)
+            Assert.Equal(Blocks.Water.Id, c[i, i, i]);
+    }
+
+    [Fact]
+    public void WormCaves_RespectsBedrockFloor()
+    {
+        var carver = new CaveCarver(seed: 999, Blocks, Cfg);
+        Chunk c = MakeStoneChunk();
+
+        carver.CarveWormCaves(c, new Vector3i(0, 0, 0)); // worldY = 0..15
+
+        for (int x = 0; x < Chunk.Size; x++)
+        for (int z = 0; z < Chunk.Size; z++)
+            Assert.Equal(Blocks.Stone.Id, c[x, 0, z]); // bedrock untouched
+    }
+
+    [Fact]
+    public void WormCaves_SeamContinuity_VoxelAtSharedWorldCoord_IsSame()
+    {
+        var carver = new CaveCarver(seed: 999, Blocks, Cfg);
+        Chunk c1 = MakeStoneChunk();
+        Chunk c2 = MakeStoneChunk();
+
+        carver.CarveWormCaves(c1, new Vector3i(0, 4, 0));
+        carver.CarveWormCaves(c2, new Vector3i(1, 4, 0));
+
+        int airC1Seam = 0, airC2Seam = 0;
+        for (int y = 1; y < Chunk.Size; y++)
+        for (int z = 0; z < Chunk.Size; z++)
+        {
+            if (c1[15, y, z] == Blocks.Air.Id) airC1Seam++;
+            if (c2[0,  y, z] == Blocks.Air.Id) airC2Seam++;
+        }
+        bool bothEmpty = airC1Seam == 0 && airC2Seam == 0;
+        bool bothCarved = airC1Seam > 0 && airC2Seam > 0;
+        Assert.True(bothEmpty || bothCarved,
+            $"seam mismatch: c1={airC1Seam}, c2={airC2Seam}");
+    }
 }