fix: Fix the incorrect timestamp in Event

PiperOrigin-RevId: 791090824

Author: google-genai-bot

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

@@ -134,7 +134,7 @@ protected Single<RequestProcessingResult> preprocess(
    */
   protected Single<ResponseProcessingResult> postprocess(
       InvocationContext context,
-      Event baseEventForLlmResponse,
+      Event.Builder baseEventForLlmResponse,
       LlmRequest llmRequest,
       LlmResponse llmResponse) {
 
@@ -200,7 +200,7 @@ protected Single<ResponseProcessingResult> postprocess(
    *     callbacks. Callbacks should not rely on its ID if they create their own separate events.
    */
   private Flowable<LlmResponse> callLlm(
-      InvocationContext context, LlmRequest llmRequest, Event eventForCallbackUsage) {
+      InvocationContext context, LlmRequest llmRequest, Event.Builder eventForCallbackUsage) {
     LlmAgent agent = (LlmAgent) context.agent();
 
     return handleBeforeModelCallback(context, llmRequest, eventForCallbackUsage)
@@ -226,7 +226,10 @@ private Flowable<LlmResponse> callLlm(
                                   llmResp -> {
                                     try (Scope innerScope = llmCallSpan.makeCurrent()) {
                                       Telemetry.traceCallLlm(
-                                          context, eventForCallbackUsage.id(), llmRequest, llmResp);
+                                          context,
+                                          eventForCallbackUsage.build().id(),
+                                          llmRequest,
+                                          llmResp);
                                     }
                                   })
                               .doOnError(
@@ -251,15 +254,15 @@ private Flowable<LlmResponse> callLlm(
    * @return A {@link Single} with the callback result or {@link Optional#empty()}.
    */
   private Single<Optional<LlmResponse>> handleBeforeModelCallback(
-      InvocationContext context, LlmRequest llmRequest, Event modelResponseEvent) {
+      InvocationContext context, LlmRequest llmRequest, Event.Builder modelResponseEvent) {
     LlmAgent agent = (LlmAgent) context.agent();
 
     Optional<List<BeforeModelCallback>> callbacksOpt = agent.beforeModelCallback();
     if (callbacksOpt.isEmpty() || callbacksOpt.get().isEmpty()) {
       return Single.just(Optional.empty());
     }
 
-    Event callbackEvent = modelResponseEvent.toBuilder().build();
+    Event callbackEvent = modelResponseEvent.build();
     List<BeforeModelCallback> callbacks = callbacksOpt.get();
 
     return Flowable.fromIterable(callbacks)
@@ -284,15 +287,15 @@ private Single<Optional<LlmResponse>> handleBeforeModelCallback(
    * @return A {@link Single} with the final {@link LlmResponse}.
    */
   private Single<LlmResponse> handleAfterModelCallback(
-      InvocationContext context, LlmResponse llmResponse, Event modelResponseEvent) {
+      InvocationContext context, LlmResponse llmResponse, Event.Builder modelResponseEvent) {
     LlmAgent agent = (LlmAgent) context.agent();
     Optional<List<AfterModelCallback>> callbacksOpt = agent.afterModelCallback();
 
     if (callbacksOpt.isEmpty() || callbacksOpt.get().isEmpty()) {
       return Single.just(llmResponse);
     }
 
-    Event callbackEvent = modelResponseEvent.toBuilder().content(llmResponse.content()).build();
+    Event callbackEvent = modelResponseEvent.content(llmResponse.content()).build();
     List<AfterModelCallback> callbacks = callbacksOpt.get();
 
     return Flowable.fromIterable(callbacks)
@@ -341,13 +344,12 @@ private Flowable<Event> runOneStep(InvocationContext context) {
                 return Flowable.fromIterable(preEvents).concatWith(Flowable.error(e));
               }
 
-              final Event mutableEventTemplate =
+              final Event.Builder mutableEventTemplate =
                   Event.builder()
                       .id(Event.generateEventId())
                       .invocationId(context.invocationId())
                       .author(context.agent().name())
-                      .branch(context.branch())
-                      .build();
+                      .branch(context.branch());
 
               Flowable<Event> restOfFlow =
                   callLlm(context, llmRequestAfterPreprocess, mutableEventTemplate)
@@ -363,13 +365,14 @@ private Flowable<Event> runOneStep(InvocationContext context) {
                             return postResultSingle
                                 .doOnSuccess(
                                     ignored -> {
-                                      String oldId = mutableEventTemplate.id();
-                                      mutableEventTemplate.setId(Event.generateEventId());
+                                      String oldId = mutableEventTemplate.build().id();
+                                      String newId = Event.generateEventId();
+                                      mutableEventTemplate.id(newId);
                                       logger.debug(
                                           "Updated mutableEventTemplate ID from {} to {} for next"
                                               + " LlmResponse",
                                           oldId,
-                                          mutableEventTemplate.id());
+                                          newId);
                                     })
                                 .toFlowable();
                           })
@@ -534,8 +537,8 @@ public void onError(Throwable e) {
                       .receive()
                       .flatMapSingle(
                           llmResponse -> {
-                            Event baseEventForThisLlmResponse =
-                                liveEventBuilderTemplate.id(Event.generateEventId()).build();
+                            Event.Builder baseEventForThisLlmResponse =
+                                liveEventBuilderTemplate.id(Event.generateEventId());
                             return postprocess(
                                 invocationContext,
                                 baseEventForThisLlmResponse,
@@ -596,9 +599,9 @@ public void onError(Throwable e) {
    * @return A fully constructed {@link Event} representing the LLM response.
    */
   private Event buildModelResponseEvent(
-      Event baseEventForLlmResponse, LlmRequest llmRequest, LlmResponse llmResponse) {
+      Event.Builder baseEventForLlmResponse, LlmRequest llmRequest, LlmResponse llmResponse) {
     Event.Builder eventBuilder =
-        baseEventForLlmResponse.toBuilder()
+        baseEventForLlmResponse
             .content(llmResponse.content())
             .partial(llmResponse.partial())
             .errorCode(llmResponse.errorCode())