test: add process context preservation test for registerAttributeKeys

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

Author: jbachorik

ddprof-test/src/test/java/com/datadoghq/profiler/context/ProcessContextTest.java

@@ -105,4 +105,41 @@ public void testNativeReadBackFunctionality() {
         assertEquals(tracerVersion, readContext.telemetrySdkVersion, "Tracer version should match");
         assertEquals("dd-trace-java", readContext.telemetrySdkName, "Tracer name should match");
     }
+
+    /**
+     * Tests that registerAttributeKeys correctly updates the process context.
+     * registerAttributeKeys reads the existing process context and republishes it
+     * with thread_ctx_config set. This test verifies that all original process
+     * context fields are preserved after that republish.
+     */
+    @Test
+    public void testRegisterAttributeKeysSetsProcessContext() {
+        Assumptions.assumeTrue(Platform.isLinux());
+
+        String env = "attr-keys-env";
+        String hostname = "attr-keys-host";
+        String runtimeId = "attr-keys-instance";
+        String service = "attr-keys-service";
+        String version = "2.0.0";
+        String tracerVersion = "4.1.0";
+
+        OTelContext context = OTelContext.getInstance();
+        context.setProcessContext(env, hostname, runtimeId, service, version, tracerVersion);
+
+        // registerAttributeKeys reads the existing process context and republishes
+        // it with thread_ctx_config populated. All original fields must survive.
+        context.registerAttributeKeys("http.route", "db.system");
+
+        OTelContext.ProcessContext readContext = context.readProcessContext();
+
+        assertNotNull(readContext, "Process context must still be readable after registerAttributeKeys");
+        assertEquals(env, readContext.deploymentEnvironmentName, "Environment name must survive registerAttributeKeys");
+        assertEquals(hostname, readContext.hostName, "Host name must survive registerAttributeKeys");
+        assertEquals(runtimeId, readContext.serviceInstanceId, "Service instance ID must survive registerAttributeKeys");
+        assertEquals(service, readContext.serviceName, "Service name must survive registerAttributeKeys");
+        assertEquals(version, readContext.serviceVersion, "Service version must survive registerAttributeKeys");
+        assertEquals("java", readContext.telemetrySdkLanguage, "Tracer language must survive registerAttributeKeys");
+        assertEquals(tracerVersion, readContext.telemetrySdkVersion, "Tracer version must survive registerAttributeKeys");
+        assertEquals("dd-trace-java", readContext.telemetrySdkName, "Tracer name must survive registerAttributeKeys");
+    }
 }