feat: add JazzerApiException for API error handling

Introduce JazzerApiException to distinguish API misuse errors (invalid
arguments, incompatible runtime) from findings in the code under test.
The fuzzing engine treats this exception as a fatal error rather than
a reportable bug.

Author: kyakdan

src/main/java/com/code_intelligence/jazzer/api/BUILD.bazel

@@ -46,6 +46,7 @@ java_library(
         "FuzzerSecurityIssueMedium.java",
         "HookType.java",
         "Jazzer.java",
+        "JazzerApiException.java",
         "MethodHook.java",
         "MethodHooks.java",
         "//src/main/java/jaz",

src/main/java/com/code_intelligence/jazzer/api/JazzerApiException.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2026 Code Intelligence GmbH
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.code_intelligence.jazzer.api;
+
+/**
+ * Signals error from the Jazzer API (e.g. invalid arguments to {@link Jazzer#maximize}).
+ *
+ * <p>This exception is treated as a fatal error by the fuzzing engine rather than as a finding in
+ * the code under test. When thrown during fuzzing, it stops the current fuzz test with an error
+ * instead of reporting a bug in the fuzz target.
+ */
+public final class JazzerApiException extends RuntimeException {
+  public JazzerApiException(String message) {
+    super(message);
+  }
+
+  public JazzerApiException(String message, Throwable cause) {
+    super(message, cause);
+  }
+
+  public JazzerApiException(Throwable cause) {
+    super(cause);
+  }
+}

src/main/java/com/code_intelligence/jazzer/driver/FuzzTargetRunner.java

@@ -16,6 +16,7 @@
 
 package com.code_intelligence.jazzer.driver;
 
+import static com.code_intelligence.jazzer.driver.Constants.JAZZER_ERROR_EXIT_CODE;
 import static com.code_intelligence.jazzer.driver.Constants.JAZZER_FINDING_EXIT_CODE;
 import static com.code_intelligence.jazzer.runtime.Constants.IS_ANDROID;
 import static java.lang.System.exit;
@@ -91,6 +92,8 @@ public final class FuzzTargetRunner {
 
   private static final String OPENTEST4J_TEST_ABORTED_EXCEPTION =
       "org.opentest4j.TestAbortedException";
+  private static final String JAZZER_API_EXCEPTION =
+      "com.code_intelligence.jazzer.api.JazzerApiException";
 
   private static final Unsafe UNSAFE = UnsafeProvider.getUnsafe();
 
@@ -271,6 +274,16 @@ private static int runOne(long dataPtr, int dataLength) {
       finding = JazzerInternal.lastFinding;
       JazzerInternal.lastFinding = null;
     }
+    // JazzerApiException signals API error, not a finding in the code under test.
+    if (finding != null && finding.getClass().getName().equals(JAZZER_API_EXCEPTION)) {
+      Log.error("Jazzer API error", finding);
+      temporarilyDisableLibfuzzerExitHook();
+      if (fatalFindingHandlerForJUnit != null) {
+        fatalFindingHandlerForJUnit.accept(finding);
+        return LIBFUZZER_RETURN_FROM_DRIVER;
+      }
+      exit(JAZZER_ERROR_EXIT_CODE);
+    }
     // Allow skipping invalid inputs in fuzz tests by using e.g. JUnit's assumeTrue.
     if (finding == null || finding.getClass().getName().equals(OPENTEST4J_TEST_ABORTED_EXCEPTION)) {
       return LIBFUZZER_CONTINUE;

src/main/java/com/code_intelligence/jazzer/junit/FuzzTestExecutor.java

@@ -52,6 +52,8 @@
 import org.junit.platform.commons.support.AnnotationSupport;
 
 class FuzzTestExecutor {
+  private static final String JAZZER_API_EXCEPTION =
+      "com.code_intelligence.jazzer.api.JazzerApiException";
   private static final AtomicBoolean hasBeenPrepared = new AtomicBoolean();
   private static final AtomicBoolean agentInstalled = new AtomicBoolean(false);
 
@@ -334,6 +336,9 @@ public Optional<Throwable> execute(
     Throwable finding = atomicFinding.get();
 
     if (finding != null) {
+      if (finding.getClass().getName().equals(JAZZER_API_EXCEPTION)) {
+        return Optional.of(finding);
+      }
       return Optional.of(new FuzzTestFindingException(finding));
     } else if (exitCode != 0) {
       return Optional.of(

src/main/java/com/code_intelligence/jazzer/junit/FuzzTestExtensions.java

@@ -42,6 +42,8 @@ class FuzzTestExtensions
     implements ExecutionCondition, InvocationInterceptor, TestExecutionExceptionHandler {
   private static final String JAZZER_INTERNAL =
       "com.code_intelligence.jazzer.runtime.JazzerInternal";
+  private static final String JAZZER_API_EXCEPTION =
+      "com.code_intelligence.jazzer.api.JazzerApiException";
   private static final AtomicReference<Method> fuzzTestMethod = new AtomicReference<>();
   private static Field lastFindingField;
   private static Field hooksEnabledField;
@@ -114,6 +116,10 @@ private static void runWithHooks(Invocation<Void> invocation) throws Throwable {
     } catch (Throwable t) {
       thrown = t;
     }
+    // JazzerApiException signals API error, so propagate as is and not as a finding.
+    if (thrown != null && thrown.getClass().getName().equals(JAZZER_API_EXCEPTION)) {
+      throw thrown;
+    }
     Throwable stored = (Throwable) getLastFindingField().get(null);
     if (stored != null) {
       throw new FuzzTestFindingException(stored);