Palette section buffer

- Add SectionBuffer: chunk palette of written instances and short[4096] ids per section in y, z, x order
- Column tops are indexed per x-slice and padded so fan-out slices do not share a cache line
- Add ColumnRunHunk and forward column runs through the listening hunk and block update listener
- Terrain painter emits column runs and evaluates ores only inside the column's ore bands
- Bukkit generation writes into SectionBuffer and applies it through ChunkDataOutput
- Remove ChunkDataHunkHolder and the probe's ProductionBlockHunk copy
- Probe production buffers use SectionBuffer

probe/src/main/java/art/arcane/iris/probe/ProbeChunkGenerator.java

@@ -18,6 +18,7 @@
 
 package art.arcane.iris.probe;
 
+import art.arcane.iris.generation.chunk.SectionBuffer;
 import art.arcane.iris.generation.context.IrisContext;
 import art.arcane.iris.generation.runtime.Engine;
 import art.arcane.iris.generation.runtime.GenerationSessionLease;
@@ -70,7 +71,7 @@ final class ProbeChunkGenerator {
     }
 
     private Hunk<NativeBlockState> newBlocks(int height) {
-        return productionBuffers ? new ProductionBlockHunk(height) : Hunk.newArrayHunk(16, height, 16);
+        return productionBuffers ? new SectionBuffer(height) : Hunk.newArrayHunk(16, height, 16);
     }
 
     private Hunk<NativeBiome> newBiomes(int height) {

probe/src/main/java/art/arcane/iris/probe/ProductionBlockHunk.java

@@ -1,86 +0,0 @@
-/*
- * Iris is a World Generator for Minecraft Servers
- * Copyright (c) 2026 Arcane Arts (Volmit Software)
- *
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program.  If not, see <https://www.gnu.org/licenses/>.
- */
-
-package art.arcane.iris.probe;
-
-import art.arcane.iris.generation.block.BoundBlockState;
-import art.arcane.iris.generation.chunk.ColumnExtent;
-import art.arcane.volmlib.nativelib.terrain.NativeBlockState;
-import art.arcane.volmlib.nativelib.terrain.NativeBlockVolume;
-import art.arcane.volmlib.util.hunk.storage.StorageHunk;
-
-import java.lang.invoke.MethodHandles;
-import java.lang.invoke.VarHandle;
-import java.util.Arrays;
-
-final class ProductionBlockHunk extends StorageHunk<NativeBlockState> implements NativeBlockVolume, ColumnExtent {
-    private static final BoundBlockState AIR = BoundBlockState.of("AIR");
-    private static final VarHandle COLUMN_TOPS = MethodHandles.arrayElementVarHandle(int[].class);
-
-    private final NativeBlockState[] data;
-    private final int[] columnTops;
-    private final int zStride;
-
-    ProductionBlockHunk(int height) {
-        super(16, height, 16);
-        this.zStride = 16 * height;
-        this.data = new NativeBlockState[zStride * 16];
-        this.columnTops = new int[256];
-        Arrays.fill(columnTops, -1);
-    }
-
-    @Override
-    public void setRaw(int x, int y, int z, NativeBlockState t) {
-        if (t == null) {
-            return;
-        }
-        data[index(x, y, z)] = t;
-        int column = (z << 4) | x;
-        int top = (int) COLUMN_TOPS.getOpaque(columnTops, column);
-        while (y > top) {
-            int witness = (int) COLUMN_TOPS.compareAndExchange(columnTops, column, top, y);
-            if (witness == top) {
-                break;
-            }
-            top = witness;
-        }
-    }
-
-    @Override
-    public NativeBlockState getRaw(int x, int y, int z) {
-        if (y < 0 || y >= getHeight()) {
-            return AIR.get();
-        }
-        NativeBlockState state = data[index(x, y, z)];
-        return state != null ? state : AIR.get();
-    }
-
-    @Override
-    public NativeBlockState getStoredRaw(int x, int y, int z) {
-        return data[index(x, y, z)];
-    }
-
-    @Override
-    public int highestStoredY(int x, int z) {
-        return (int) COLUMN_TOPS.getOpaque(columnTops, (z << 4) | x);
-    }
-
-    private int index(int x, int y, int z) {
-        return (z * zStride) + (y << 4) + x;
-    }
-}

probe/src/test/java/art/arcane/iris/probe/ProductionHunkTest.java

@@ -1,5 +1,6 @@
 package art.arcane.iris.probe;
 
+import art.arcane.iris.generation.chunk.SectionBuffer;
 import art.arcane.volmlib.nativelib.terrain.NativeBiome;
 import art.arcane.volmlib.nativelib.terrain.NativeBlockState;
 import art.arcane.volmlib.util.hunk.Hunk;
@@ -19,7 +20,7 @@ public final class ProductionHunkTest {
 
     @Test
     public void blockHunkIgnoresNullWritesAndTracksTheHighestStoredCellPerColumn() {
-        ProductionBlockHunk blocks = new ProductionBlockHunk(HEIGHT);
+        SectionBuffer blocks = new SectionBuffer(HEIGHT);
         NativeBlockState stone = StubPlatform.blockStateForTest("minecraft:stone");
         NativeBlockState dirt = StubPlatform.blockStateForTest("minecraft:dirt");
 
@@ -37,7 +38,7 @@ public final class ProductionHunkTest {
 
     @Test
     public void dumpCaptureOfTheBlockHunkMatchesAnArrayHunkHoldingTheSameWrites() {
-        ProductionBlockHunk production = new ProductionBlockHunk(HEIGHT);
+        SectionBuffer production = new SectionBuffer(HEIGHT);
         Hunk<NativeBlockState> array = Hunk.newArrayHunk(16, HEIGHT, 16);
         Hunk<NativeBiome> biomes = Hunk.newArrayHunk(16, HEIGHT, 16);
         NativeBlockState stone = StubPlatform.blockStateForTest("minecraft:stone");