fix: Bypass redundant getSession read in ADK Runner

Bypass the sequential getSession database call after appending a message in Runner.runAsyncImpl to save one network roundtrip (~170ms).

PiperOrigin-RevId: 927833117

Author: google-genai-bot

core/src/main/java/com/google/adk/runner/Runner.java

@@ -518,18 +518,9 @@ protected Flowable<Event> runAsyncImpl(
                               runConfig.saveInputBlobsAsArtifacts(),
                               stateDelta))
                   .flatMapPublisher(
-                      event -> {
-                        // Get the updated session after the message and state delta are
-                        // applied
-                        return this.sessionService
-                            .getSession(
-                                session.appName(), session.userId(), session.id(), Optional.empty())
-                            .flatMapPublisher(
-                                updatedSession ->
-                                    runAgentWithUpdatedSession(
-                                        initialContext, updatedSession, event, rootAgent))
-                            .compose(Tracing.<Event>withContext(capturedContext));
-                      });
+                      event ->
+                          runAgentWithUpdatedSession(initialContext, session, event, rootAgent)
+                              .compose(Tracing.<Event>withContext(capturedContext)));
             })
         .doOnError(
             throwable -> {

core/src/test/java/com/google/adk/runner/RunnerTest.java

@@ -763,8 +763,11 @@ public void runAsync_concurrentCalls_staleRead() throws Exception {
                   .firstOrError()
                   .doOnSuccess(
                       event -> {
+                        s.events().add(e);
+                        if (e.actions() != null && e.actions().stateDelta() != null) {
+                          s.state().putAll(e.actions().stateDelta());
+                        }
                         List<Event> newEvents = new ArrayList<>(s.events());
-                        newEvents.add(e);
                         Session updated =
                             Session.builder(s.id())
                                 .appName(s.appName())
@@ -1193,6 +1196,41 @@ public void runAsync_pureMockSessionService_multiStepLlmAgent_appendsExactlyOnce
     verify(pureMockSessionService, times(expectedAppendCount)).appendEvent(any(), any());
   }
 
+  @Test
+  public void runAsync_bypassesRedundantGetSession() {
+    BaseSessionService mockSessionService = mock(BaseSessionService.class);
+    Session backingSession = Session.builder("session-id").appName("test").userId("user").build();
+
+    when(mockSessionService.getSession(anyString(), anyString(), anyString(), any()))
+        .thenReturn(Maybe.just(backingSession));
+    when(mockSessionService.appendEvent(any(), any()))
+        .thenReturn(Single.just(Event.builder().id("sentinel").author("user").build()));
+
+    BaseAgent mockAgent = mock(BaseAgent.class);
+    when(mockAgent.runAsync(any()))
+        .thenReturn(Flowable.just(Event.builder().id("agent-event").author("agent").build()));
+
+    Runner spyRunner =
+        Runner.builder()
+            .app(
+                App.builder()
+                    .name("test")
+                    .rootAgent(mockAgent)
+                    .plugins(ImmutableList.of(plugin))
+                    .build())
+            .sessionService(mockSessionService)
+            .build();
+
+    List<Event> unused =
+        spyRunner
+            .runAsync("user", backingSession.id(), createContent("from user"))
+            .toList()
+            .blockingGet();
+
+    // Verify getSession was only called once (at the start of runAsync)
+    verify(mockSessionService, times(1)).getSession(anyString(), anyString(), anyString(), any());
+  }
+
   @Test
   public void runAsync_withSessionKey_success() {
     var events =