Compact actual Creative history and diagnose player-save exceptions

Fix compaction after the earlier history bound; validate the rendered observation to catch interactions between patches. Add a small reproducible Java 17 agent that exposes the exception swallowed by vanilla player saving, preserving catch behavior. Regression and diagnostic-agent tests passed.

diagnostics/PlayerSaveDiagnostics.java

@@ -0,0 +1,58 @@
+import java.lang.instrument.ClassFileTransformer;
+import java.lang.instrument.Instrumentation;
+import java.security.ProtectionDomain;
+import java.util.HashSet;
+import java.util.Set;
+import jdk.internal.org.objectweb.asm.*;
+
+/** Log the exception vanilla 1.19 discards when player saving fails. */
+public final class PlayerSaveDiagnostics {
+    public static void premain(String args, Instrumentation instrumentation) {
+        instrumentation.addTransformer(new ClassFileTransformer() {
+            public byte[] transform(ClassLoader loader, String name, Class<?> type,
+                                    ProtectionDomain domain, byte[] bytes) {
+                if (!"net/minecraft/class_29".equals(name)) return null;
+                try {
+                    ClassReader reader = new ClassReader(bytes);
+                    ClassWriter writer = new ClassWriter(reader, ClassWriter.COMPUTE_MAXS);
+                    int[] injected = {0};
+                    reader.accept(new ClassVisitor(Opcodes.ASM8, writer) {
+                        public MethodVisitor visitMethod(int access, String method, String desc,
+                                                         String signature, String[] exceptions) {
+                            MethodVisitor delegate = super.visitMethod(access, method, desc, signature, exceptions);
+                            if (!"method_262".equals(method)) return delegate;
+                            return new MethodVisitor(Opcodes.ASM8, delegate) {
+                                final Set<Label> handlers = new HashSet<>();
+                                boolean pending;
+                                public void visitTryCatchBlock(Label start, Label end, Label handler, String caught) {
+                                    if ("java/lang/Exception".equals(caught)) handlers.add(handler);
+                                    super.visitTryCatchBlock(start, end, handler, caught);
+                                }
+                                public void visitLabel(Label label) {
+                                    super.visitLabel(label);
+                                    if (handlers.contains(label)) pending = true;
+                                }
+                                public void visitVarInsn(int opcode, int variable) {
+                                    if (pending && opcode == Opcodes.ASTORE) {
+                                        // Preserve the original exception and catch behavior.
+                                        super.visitInsn(Opcodes.DUP);
+                                        super.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/lang/Throwable",
+                                                              "printStackTrace", "()V", false);
+                                        pending = false;
+                                        injected[0]++;
+                                    }
+                                    super.visitVarInsn(opcode, variable);
+                                }
+                            };
+                        }
+                    }, 0);
+                    System.err.println("[player-save-diagnostics] exception logging hooks=" + injected[0]);
+                    return injected[0] == 0 ? null : writer.toByteArray();
+                } catch (Throwable failure) {
+                    System.err.println("[player-save-diagnostics] skipped: " + failure);
+                    return null;
+                }
+            }
+        });
+    }
+}

diagnostics/build.py

@@ -0,0 +1,22 @@
+"""Reproducibly build the Java 17 diagnostic agent; no Minecraft dependencies."""
+from pathlib import Path
+import subprocess
+import tempfile
+import zipfile
+
+root = Path(__file__).resolve().parent
+with tempfile.TemporaryDirectory() as directory:
+    subprocess.run([
+        "java", "-m", "jdk.compiler/com.sun.tools.javac.Main",
+        "--add-exports", "java.base/jdk.internal.org.objectweb.asm=ALL-UNNAMED",
+        "-source", "17", "-target", "17", "-d", directory,
+        str(root / "PlayerSaveDiagnostics.java"),
+    ], check=True)
+    with zipfile.ZipFile(root / "player-save-diagnostics.jar", "w", zipfile.ZIP_DEFLATED) as archive:
+        def write(name, data):
+            entry = zipfile.ZipInfo(name, (2026, 1, 1, 0, 0, 0))
+            entry.compress_type = zipfile.ZIP_DEFLATED
+            archive.writestr(entry, data)
+        write("META-INF/MANIFEST.MF", b"Manifest-Version: 1.0\nPremain-Class: PlayerSaveDiagnostics\n\n")
+        for path in sorted(Path(directory).glob("*.class")):
+            write(path.name, path.read_bytes())

minecraft_stack.py

@@ -362,7 +362,10 @@ class MinecraftStack:
         READY_FILE.unlink(missing_ok=True)
         proc = self._spawn(
             "minecraft",
-            [str(self._ensure_minecraft_java()), "-Xms1G", "-Xmx8G", "-jar", str(launcher), "nogui"],
+            [str(self._ensure_minecraft_java()), "-Xms1G", "-Xmx8G",
+             "--add-exports=java.base/jdk.internal.org.objectweb.asm=ALL-UNNAMED",
+             f"-javaagent:{Path(__file__).resolve().parent / 'diagnostics/player-save-diagnostics.jar'}",
+             "-jar", str(launcher), "nogui"],
             JAVA_DIR,
         )
         if not _wait_tcp("127.0.0.1", 25565, 120):

tests/test_player_save_diagnostics.py

@@ -0,0 +1,31 @@
+"""Verify exception logging does not replace vanilla's catch or success path."""
+from pathlib import Path
+import subprocess
+import tempfile
+
+root = Path(__file__).resolve().parents[1]
+with tempfile.TemporaryDirectory() as directory:
+    folder = Path(directory)
+    source = folder / "class_29.java"
+    source.write_text('''package net.minecraft;
+public class class_29 {
+  public void method_262(boolean fail) {
+    try { if(fail) throw new java.io.IOException("diagnostic sentinel"); }
+    catch(Exception e) { System.out.println("original catch retained"); }
+  }
+  public static void main(String[] args) {
+    new class_29().method_262(true);
+    new class_29().method_262(false);
+    System.out.println("normal return retained");
+  }
+}''')
+    subprocess.run(["java", "-m", "jdk.compiler/com.sun.tools.javac.Main", "-d", directory, str(source)], check=True)
+    result = subprocess.run([
+        "java", "--add-exports=java.base/jdk.internal.org.objectweb.asm=ALL-UNNAMED",
+        f"-javaagent:{root / 'diagnostics/player-save-diagnostics.jar'}",
+        "-cp", directory, "net.minecraft.class_29",
+    ], capture_output=True, text=True, check=True)
+    assert result.stderr.count("java.io.IOException: diagnostic sentinel") == 1
+    assert "exception logging hooks=1" in result.stderr
+    assert result.stdout == "original catch retained\nnormal return retained\n"
+    print("PASS player-save exception visible; original catch and normal return unchanged")

tests/test_voyager_patch.py

@@ -111,9 +111,9 @@ def test_resume():
 def check_curriculum_behavior(source):
     tree = ast.parse(source)
     cls = next(n for n in tree.body if isinstance(n, ast.ClassDef) and n.name == "CurriculumAgent")
-    names = {"get_task_context", "propose_next_ai_task", "parse_ai_message", "render_human_message"}
+    names = {"get_task_context", "propose_next_ai_task", "parse_ai_message", "render_human_message", "render_observation"}
     methods = [n for n in cls.body if isinstance(n, ast.FunctionDef) and n.name in names]
-    ns = {"AIMessage": SimpleNamespace, "HumanMessage": SimpleNamespace, "validate_task": validate_task}
+    ns = {"AIMessage": SimpleNamespace, "HumanMessage": SimpleNamespace, "validate_task": validate_task, "task_history": task_history}
     exec(compile(ast.Module(body=methods, type_ignores=[]), "curriculum.py", "exec"), ns)
     agent = SimpleNamespace(completed_tasks=["Obtain a spruce log"], failed_tasks=[])
     for name in names:
@@ -128,6 +128,14 @@ def check_curriculum_behavior(source):
     retry = agent.llm.call_args_list[1].args[0]
     assert len(retry) == 4 and "Task already completed" in retry[-1].content
     assert len(messages) == 2
+    agent.progress = 100
+    agent.warm_up = {"optional_inventory_items": 0}
+    agent.completed_tasks = ["Mine 1 stone block to craft and upgrade tools", "Mine 1 stone"]
+    observed = {"status": {"biome": "snowy_plains", "timeOfDay": "sunrise", "entities": {}, "health": 20,
+                "food": 20, "position": {"x": 0, "y": 74, "z": 0}, "equipment": [], "inventoryUsed": 0},
+                "voxels": ["stone", "grass_block"], "blockRecords": [], "inventory": {}}
+    observation = agent.render_observation(events=[["observe", observed]], chest_observation="")
+    assert observation["completed_tasks"] == "Completed tasks so far: Mine 1 stone\n\n"
     agent.run_qa = Mock(side_effect=AssertionError("Survival QA must not run"))
     agent.run_qa_step2_answer_questions = agent.run_qa
     agent.render_observation = Mock(return_value={"inventory": "Inventory: netherite tools"})

voyager_stack.py

@@ -515,11 +515,11 @@ async function exploreUntil(bot, direction, maxTime = 60, callback) {
         curriculum_text = curriculum_path.read_text(encoding="utf-8")
         curriculum_text = curriculum_text.replace(
             '", ".join(self.completed_tasks) if self.completed_tasks else "None"',
-            '", ".join(list(dict.fromkeys(self.completed_tasks))[-20:]) if self.completed_tasks else "None"',
+            'task_history(self.completed_tasks) if self.completed_tasks else "None"',
         )
         curriculum_text = curriculum_text.replace(
             'failed_tasks = ", ".join(self.failed_tasks) if self.failed_tasks else "None"',
-            'failed_tasks = ", ".join(list(dict.fromkeys(self.failed_tasks))[-20:]) if self.failed_tasks else "None"',
+            'failed_tasks = task_history(self.failed_tasks) if self.failed_tasks else "None"',
         )
 
         creative_context_method = '''    def get_task_context(self, task):