fix: Ensure callbackContextData is preserved across session update

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

@@ -477,13 +477,8 @@ protected Flowable<Event> runAsyncImpl(
                                 session.appName(), session.userId(), session.id(), Optional.empty())
                             .flatMapPublisher(
                                 updatedSession ->
-                                    runAgentWithFreshSession(
-                                        session,
-                                        updatedSession,
-                                        event,
-                                        invocationId,
-                                        runConfig,
-                                        rootAgent))
+                                    runAgentWithUpdatedSession(
+                                        initialContext, updatedSession, event, rootAgent))
                             .compose(Tracing.<Event>withContext(capturedContext));
                       });
             })
@@ -495,19 +490,27 @@ protected Flowable<Event> runAsyncImpl(
             });
   }
 
-  private Flowable<Event> runAgentWithFreshSession(
-      Session session,
-      Session updatedSession,
-      Event event,
-      String invocationId,
-      RunConfig runConfig,
-      BaseAgent rootAgent) {
+  /**
+   * Runs the agent with the updated session state.
+   *
+   * <p>This method is called after the user message has been persistent in the session. It creates
+   * a final {@link InvocationContext} that inherits state from the {@code initialContext} but uses
+   * the {@code updatedSession} to ensure the agent can access the latest conversation history.
+   *
+   * @param initialContext the context from the start of the invocation, used to preserve metadata
+   *     and callback data.
+   * @param updatedSession the session object containing the latest message.
+   * @param event the event representing the user message that was just appended.
+   * @param rootAgent the agent to be executed.
+   * @return a stream of events from the agent execution and subsequent plugin callbacks.
+   */
+  private Flowable<Event> runAgentWithUpdatedSession(
+      InvocationContext initialContext, Session updatedSession, Event event, BaseAgent rootAgent) {
     // Create context with updated session for beforeRunCallback
     InvocationContext contextWithUpdatedSession =
-        newInvocationContextBuilder(updatedSession)
-            .invocationId(invocationId)
+        initialContext.toBuilder()
+            .session(updatedSession)
             .agent(this.findAgentToRun(updatedSession, rootAgent))
-            .runConfig(runConfig)
             .userContent(event.content().orElseGet(Content::fromParts))
             .build();
 
@@ -536,7 +539,7 @@ private Flowable<Event> runAgentWithFreshSession(
                         .flatMap(
                             registeredEvent -> {
                               // TODO: remove this hack after deprecating runAsync with Session.
-                              copySessionStates(updatedSession, session);
+                              copySessionStates(updatedSession, initialContext.session());
                               return contextWithUpdatedSession
                                   .pluginManager()
                                   .onEventCallback(contextWithUpdatedSession, registeredEvent)

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

@@ -591,6 +591,29 @@ public void onEventCallback_success() {
     verify(plugin).onEventCallback(any(), any());
   }
 
+  @Test
+  public void callbackContextData_preservedAcrossInvocation() {
+    String testKey = "testKey";
+    String testValue = "testValue";
+
+    when(plugin.onUserMessageCallback(any(), any()))
+        .thenAnswer(
+            invocation -> {
+              InvocationContext context = invocation.getArgument(0);
+              context.callbackContextData().put(testKey, testValue);
+              return Maybe.empty();
+            });
+
+    ArgumentCaptor<InvocationContext> contextCaptor =
+        ArgumentCaptor.forClass(InvocationContext.class);
+    when(plugin.afterRunCallback(contextCaptor.capture())).thenReturn(Completable.complete());
+
+    var unused =
+        runner.runAsync("user", session.id(), createContent("test")).toList().blockingGet();
+
+    assertThat(contextCaptor.getValue().callbackContextData()).containsEntry(testKey, testValue);
+  }
+
   @Test
   public void runAsync_withSessionKey_success() {
     var events =