Warn about unsupported blocks after chunk loading (#1880)

* feat: warn about unsupported blocks after chunk loading

Track block names that are not recognized by any BlockProvider in a
concurrent set within BlockPalette. After chunk loading completes, log a
warning listing the unsupported block names and suggesting the user
update Chunky or check the minecraft label on GitHub.

Fixes #1801

* refactor: move unsupported blocks check into loadChunks, use HashSet

Address review feedback from @NotStirred:
- Move unsupported blocks warning from Scene caller into loadChunks itself,
  since the check should run for all callers, not just the scene reload path
- Change unsupportedBlocks from ConcurrentHashMap.newKeySet() to HashSet
  since put() locks internally and all puts complete before getUnsupportedBlocks

Signed-off-by: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Signed-off-by: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>
Co-authored-by: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: mvanhorn

chunky/src/java/se/llbit/chunky/chunk/BlockPalette.java

@@ -64,6 +64,7 @@ public class BlockPalette {
 
   private final Map<BlockSpec, Integer> blockMap;
   private List<Block> palette;
+  private final Set<String> unsupportedBlocks = new HashSet<>();
 
   private ReentrantLock lock = new ReentrantLock();
 
@@ -131,6 +132,9 @@ public int put(BlockSpec spec) {
       id = palette.size();
       blockMap.put(spec, id);
       Block block = spec.toBlock();
+      if (block instanceof UnknownBlock) {
+        unsupportedBlocks.add(block.name);
+      }
       applyMaterial(block);
       palette.add(block);
       return id;
@@ -139,6 +143,14 @@ public int put(BlockSpec spec) {
     }
   }
 
+  /**
+   * Returns the set of block names that were not recognized by any block provider.
+   * These blocks are rendered as {@link UnknownBlock}.
+   */
+  public Set<String> getUnsupportedBlocks() {
+    return Collections.unmodifiableSet(unsupportedBlocks);
+  }
+
   public Block get(int id) {
     if (id == ANY_ID)
       return stone;

chunky/src/java/se/llbit/chunky/renderer/scene/Scene.java

@@ -1466,6 +1466,14 @@ public synchronized void loadChunks(TaskTracker taskTracker, World world, Map<Re
 
     importMaterials();
 
+    if (palette != null) {
+      Set<String> unsupported = palette.getUnsupportedBlocks();
+      if (!unsupported.isEmpty()) {
+        Log.warn("Unsupported blocks found: " + String.join(", ", unsupported)
+            + ". Consider updating Chunky or check https://github.com/chunky-dev/chunky/labels/minecraft for known issues.");
+      }
+    }
+
     isLoading = false;
   }