Fix live heap enablement logic for Java 8 and unsafe JVM versions

- On Java 8, neither ddprof MEMLEAK (requires Java 11+) nor JFR
  OldObjectSample is available; explicitly enabling profiling.heap.enabled
  now logs a warning instead of silently enabling an unsupported event
- ddprofLikelyActive heuristic uses isJmethodIDSafe() as the default for
  the liveheap flag (was hardcoded true), matching ddprof's own resolution
  and preventing false disablement of OldObjectSample on Java 11.0.12-11.0.22
  and 17.0.3-17.0.10
- Fix testHeapProfilerIsStillOverriddenThroughConfig to expect
  isOldObjectSampleAvailable() instead of unconditional true

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: jbachorik

dd-java-agent/agent-profiling/profiling-controller-openjdk/src/main/java/com/datadog/profiling/controller/openjdk/OpenJdkController.java

@@ -202,17 +202,25 @@ ProfilingConfig.PROFILING_HEAP_ENABLED, isLiveHeapProfilingSafe())) {
       disableEvent(recordingSettings, "jdk.OldObjectSample", "live heap profiling is disabled");
     } else {
       // ddprof live heap requires Java 11+ (JVMTI Allocation Sampler)
+      // isJmethodIDSafe() matches ddprof's own default for liveheap: it only enables
+      // MEMLEAK mode by default on versions where jmethodID is safe.
       boolean ddprofLikelyActive =
           isJavaVersionAtLeast(11)
               && configProvider.getBoolean(
-                  ProfilingConfig.PROFILING_DATADOG_PROFILER_LIVEHEAP_ENABLED, true)
+                  ProfilingConfig.PROFILING_DATADOG_PROFILER_LIVEHEAP_ENABLED, isJmethodIDSafe())
               && configProvider.getBoolean(
                   ProfilingConfig.PROFILING_DATADOG_PROFILER_ENABLED, true);
       if (ddprofLikelyActive) {
         disableEvent(
             recordingSettings,
             "jdk.OldObjectSample",
             "ddprof live heap profiling is expected to handle live heap data");
+      } else if (isOldObjectSampleAvailable()) {
+        enableEvent(recordingSettings, "jdk.OldObjectSample", "heap profiling is enabled");
+      } else if (configProvider.getBoolean(ProfilingConfig.PROFILING_HEAP_ENABLED, false)) {
+        log.warn(
+            "Live heap profiling was explicitly requested but is not supported on this JVM version;"
+                + " no heap profiling data will be collected.");
       }
     }
 

dd-java-agent/agent-profiling/profiling-controller-openjdk/src/test/java/com/datadog/profiling/controller/openjdk/OpenJdkControllerTest.java

@@ -106,8 +106,11 @@ public void testHeapProfilerIsStillOverriddenThroughConfig() throws Exception {
         ((OpenJdkRecordingData)
                 controller.createRecording(TEST_NAME, new ControllerContext().snapshot()).stop())
             .getRecording()) {
+      // On JVMs where OldObjectSample is not available (e.g. Java 8), explicitly enabling heap
+      // profiling has no effect — the event cannot be safely enabled.
       assertEquals(
-          true, Boolean.parseBoolean(recording.getSettings().get("jdk.OldObjectSample#enabled")));
+          isOldObjectSampleAvailable(),
+          Boolean.parseBoolean(recording.getSettings().get("jdk.OldObjectSample#enabled")));
     }
   }