feat(world-gen): add MinCaveY ceiling to CaveCarver

VoxelEngine.Tests/WorldGen/CaveCarverTests.cs

@@ -183,4 +183,20 @@ public class CaveCarverTests
         Assert.True(bothEmpty || bothCarved,
             $"seam mismatch: c1={airC1Seam}, c2={airC2Seam}");
     }
+
+    [Fact]
+    public void Carve_RespectsMinCaveY_NoCarvingAboveCeiling()
+    {
+        var cfg = new Configuration { MinCaveY = 20 };
+        var carver = new CaveCarver(seed: 42, Blocks, cfg);
+        Chunk c = MakeStoneChunk();
+
+        // Chunk Y=2 → worldY 32..47, all above MinCaveY=20 → must stay solid.
+        carver.Carve(c, new Vector3i(0, 2, 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(Blocks.Stone.Id, c[x, y, z]);
+    }
 }