fix: ensure artifact saves complete before appending event in Runner

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

@@ -312,27 +312,27 @@ private Single<Event> appendNewMessageToSession(
       throw new IllegalArgumentException("No parts in the new_message.");
     }
 
+    List<Completable> artifactSaves = new ArrayList<>();
     if (this.artifactService != null && saveInputBlobsAsArtifacts) {
       // The runner directly saves the artifacts (if applicable) in the user message and replaces
       // the artifact data with a file name placeholder.
+      List<Part> newParts = new ArrayList<>();
       for (int i = 0; i < newMessage.parts().get().size(); i++) {
         Part part = newMessage.parts().get().get(i);
-        if (part.inlineData().isEmpty()) {
+        if (part.inlineData().isEmpty() && part.fileData().isEmpty()) {
+          newParts.add(part);
           continue;
         }
         String fileName = "artifact_" + invocationContext.invocationId() + "_" + i;
-        var unused =
-            this.artifactService.saveArtifact(
-                this.appName, session.userId(), session.id(), fileName, part);
-
-        newMessage
-            .parts()
-            .get()
-            .set(
-                i,
-                Part.fromText(
-                    "Uploaded file: " + fileName + ". It has been saved to the artifacts"));
+        artifactSaves.add(
+            this.artifactService
+                .saveArtifact(this.appName, session.userId(), session.id(), fileName, part)
+                .ignoreElement());
+
+        newParts.add(
+            Part.fromText("Uploaded file: " + fileName + ". It has been saved to the artifacts"));
       }
+      newMessage = newMessage.toBuilder().parts(newParts).build();
     }
     // Appends only. We do not yield the event because it's not from the model.
     Event.Builder eventBuilder =
@@ -348,7 +348,12 @@ private Single<Event> appendNewMessageToSession(
           EventActions.builder().stateDelta(new ConcurrentHashMap<>(stateDelta)).build());
     }
 
-    return this.sessionService.appendEvent(session, eventBuilder.build());
+    Single<Event> appendEventSingle =
+        this.sessionService.appendEvent(session, eventBuilder.build());
+    if (artifactSaves.isEmpty()) {
+      return appendEventSingle;
+    }
+    return Completable.merge(artifactSaves).andThen(appendEventSingle);
   }
 
   /** See {@link #runAsync(String, String, Content, RunConfig, Map)}. */

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

@@ -36,6 +36,7 @@
 import com.google.adk.agents.LlmAgent;
 import com.google.adk.agents.RunConfig;
 import com.google.adk.apps.App;
+import com.google.adk.artifacts.BaseArtifactService;
 import com.google.adk.events.Event;
 import com.google.adk.flows.llmflows.Functions;
 import com.google.adk.models.LlmResponse;
@@ -52,6 +53,7 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Iterables;
+import com.google.genai.types.Blob;
 import com.google.genai.types.Content;
 import com.google.genai.types.FunctionCall;
 import com.google.genai.types.FunctionResponse;
@@ -62,6 +64,7 @@
 import io.reactivex.rxjava3.core.Completable;
 import io.reactivex.rxjava3.core.Flowable;
 import io.reactivex.rxjava3.core.Maybe;
+import io.reactivex.rxjava3.core.Single;
 import io.reactivex.rxjava3.subscribers.TestSubscriber;
 import java.util.List;
 import java.util.Objects;
@@ -640,6 +643,121 @@ public void runAsync_withSessionKeyAndStateDelta_mergesStateIntoSession() {
     assertThat(finalSession.state()).containsAtLeastEntriesIn(stateDelta);
   }
 
+  @Test
+  public void runAsync_withSaveInputBlobsAsArtifactsTrue_savesBlobsAndReplacesContent() {
+    BaseArtifactService mockArtifactService = mock(BaseArtifactService.class);
+    when(mockArtifactService.saveArtifact(any(), any(), any(), any(), any()))
+        .thenReturn(Single.just(1));
+
+    Runner runnerWithMockService =
+        Runner.builder()
+            .app(
+                App.builder()
+                    .name("test")
+                    .rootAgent(agent)
+                    .plugins(ImmutableList.of(plugin))
+                    .build())
+            .artifactService(mockArtifactService)
+            .build();
+    Session localSession =
+        runnerWithMockService.sessionService().createSession("test", "user").blockingGet();
+
+    Content userContent =
+        Content.builder()
+            .role("user")
+            .parts(
+                Part.fromText("text part"),
+                Part.builder()
+                    .inlineData(
+                        Blob.builder().mimeType("image/png").data(new byte[] {1, 2, 3}).build())
+                    .build())
+            .build();
+
+    var events =
+        runnerWithMockService
+            .runAsync(
+                "user",
+                localSession.id(),
+                userContent,
+                RunConfig.builder().setSaveInputBlobsAsArtifacts(true).build())
+            .toList()
+            .blockingGet();
+
+    assertThat(simplifyEvents(events)).containsExactly("test agent: from llm");
+
+    Session finalSession =
+        runnerWithMockService
+            .sessionService()
+            .getSession("test", "user", localSession.id(), Optional.empty())
+            .blockingGet();
+
+    Event savedEvent = finalSession.events().get(0);
+    assertThat(savedEvent.author()).isEqualTo("user");
+    List<Part> parts = savedEvent.content().get().parts().get();
+    assertThat(parts).hasSize(2);
+    assertThat(parts.get(0).text()).hasValue("text part");
+    assertThat(parts.get(1).text().get()).startsWith("Uploaded file: artifact_");
+    assertThat(parts.get(1).inlineData()).isEmpty();
+
+    verify(mockArtifactService).saveArtifact(any(), any(), any(), any(), any());
+  }
+
+  @Test
+  public void runAsync_withSaveInputBlobsAsArtifactsFalse_doesNotModifyContent() {
+    BaseArtifactService mockArtifactService = mock(BaseArtifactService.class);
+
+    Runner runnerWithMockService =
+        Runner.builder()
+            .app(
+                App.builder()
+                    .name("test")
+                    .rootAgent(agent)
+                    .plugins(ImmutableList.of(plugin))
+                    .build())
+            .artifactService(mockArtifactService)
+            .build();
+    Session localSession =
+        runnerWithMockService.sessionService().createSession("test", "user").blockingGet();
+
+    Content userContent =
+        Content.builder()
+            .role("user")
+            .parts(
+                Part.fromText("text part"),
+                Part.builder()
+                    .inlineData(
+                        Blob.builder().mimeType("image/png").data(new byte[] {1, 2, 3}).build())
+                    .build())
+            .build();
+
+    var events =
+        runnerWithMockService
+            .runAsync(
+                "user",
+                localSession.id(),
+                userContent,
+                RunConfig.builder().setSaveInputBlobsAsArtifacts(false).build())
+            .toList()
+            .blockingGet();
+
+    assertThat(simplifyEvents(events)).containsExactly("test agent: from llm");
+
+    Session finalSession =
+        runnerWithMockService
+            .sessionService()
+            .getSession("test", "user", localSession.id(), Optional.empty())
+            .blockingGet();
+
+    Event savedEvent = finalSession.events().get(0);
+    assertThat(savedEvent.author()).isEqualTo("user");
+    List<Part> parts = savedEvent.content().get().parts().get();
+    assertThat(parts).hasSize(2);
+    assertThat(parts.get(0).text()).hasValue("text part");
+    assertThat(parts.get(1).inlineData().get().mimeType()).hasValue("image/png");
+
+    verify(mockArtifactService, never()).saveArtifact(any(), any(), any(), any(), any());
+  }
+
   @Test
   public void runAsync_withEmptyStateDelta_doesNotModifySession() {
     ImmutableMap<String, Object> emptyStateDelta = ImmutableMap.of();