fix: include usage_metadata events in live postprocessing

core/src/main/java/com/google/adk/flows/llmflows/BaseLlmFlow.java

@@ -611,7 +611,8 @@ private Flowable<Event> buildPostprocessingEvents(
     if (updatedResponse.content().isEmpty()
         && updatedResponse.errorCode().isEmpty()
         && !updatedResponse.interrupted().orElse(false)
-        && !updatedResponse.turnComplete().orElse(false)) {
+        && !updatedResponse.turnComplete().orElse(false)
+        && updatedResponse.usageMetadata().isEmpty()) {
       return processorEvents;
     }
 

core/src/test/java/com/google/adk/flows/llmflows/BaseLlmFlowTest.java

@@ -17,6 +17,7 @@
 package com.google.adk.flows.llmflows;
 
 import static com.google.adk.testing.TestUtils.assertEqualIgnoringFunctionIds;
+import static com.google.adk.testing.TestUtils.createGenerateContentResponseUsageMetadata;
 import static com.google.adk.testing.TestUtils.createInvocationContext;
 import static com.google.adk.testing.TestUtils.createLlmResponse;
 import static com.google.adk.testing.TestUtils.createTestAgent;
@@ -575,4 +576,32 @@ public Single<Map<String, Object>> runAsync(Map<String, Object> args, ToolContex
       return Single.just(response);
     }
   }
+
+  @Test
+  public void postprocess_noResponseProcessors_onlyUsageMetadata_returnsEvent() {
+    GenerateContentResponseUsageMetadata usageMetadata =
+        createGenerateContentResponseUsageMetadata().build();
+    LlmResponse llmResponse = LlmResponse.builder().usageMetadata(usageMetadata).build();
+    InvocationContext invocationContext =
+        createInvocationContext(createTestAgent(createTestLlm(llmResponse)));
+    BaseLlmFlow baseLlmFlow = createBaseLlmFlowWithoutProcessors();
+    Event baseEvent =
+        Event.builder()
+            .invocationId(invocationContext.invocationId())
+            .author(invocationContext.agent().name())
+            .build();
+
+    List<Event> events =
+        baseLlmFlow
+            .postprocess(invocationContext, baseEvent, LlmRequest.builder().build(), llmResponse)
+            .toList()
+            .blockingGet();
+
+    assertThat(events).hasSize(1);
+    Event event = getOnlyElement(events);
+    assertThat(event.content()).isEmpty();
+    assertThat(event.usageMetadata()).hasValue(usageMetadata);
+    assertThat(event.author()).isEqualTo(invocationContext.agent().name());
+    assertThat(event.invocationId()).isEqualTo(invocationContext.invocationId());
+  }
 }

core/src/test/java/com/google/adk/testing/TestUtils.java

@@ -41,6 +41,7 @@
 import com.google.genai.types.FunctionCall;
 import com.google.genai.types.FunctionDeclaration;
 import com.google.genai.types.FunctionResponse;
+import com.google.genai.types.GenerateContentResponseUsageMetadata;
 import com.google.genai.types.Part;
 import io.reactivex.rxjava3.core.Flowable;
 import io.reactivex.rxjava3.core.Single;
@@ -253,6 +254,13 @@ public static LlmResponse createFunctionCallLlmResponse(
     return createLlmResponse(content);
   }
 
+  public static GenerateContentResponseUsageMetadata.Builder
+      createGenerateContentResponseUsageMetadata() {
+    return GenerateContentResponseUsageMetadata.builder()
+        .promptTokenCount(10)
+        .candidatesTokenCount(20);
+  }
+
   public static class EchoTool extends BaseTool {
     public EchoTool() {
       super("echo_tool", "description");