refactor: Deprecate Optional in BaseArtifactService and CallbackContext

core/src/main/java/com/google/adk/agents/CallbackContext.java

@@ -92,14 +92,20 @@ public Single<List<String>> listArtifacts() {
         .map(ListArtifactsResponse::filenames);
   }
 
+  /** Loads the latest version of an artifact from the service. */
+  public Maybe<Part> loadArtifact(String filename) {
+    return loadArtifact(filename, Optional.empty());
+  }
+
+  /** Loads a specific version of an artifact from the service. */
+  public Maybe<Part> loadArtifact(String filename, int version) {
+    return loadArtifact(filename, Optional.of(version));
+  }
+
   /**
-   * Loads an artifact from the artifact service associated with the current session.
-   *
-   * @param filename Artifact file name.
-   * @param version Artifact version (optional).
-   * @return loaded part, or empty if not found.
-   * @throws IllegalStateException if the artifact service is not initialized.
+   * @deprecated Use {@link #loadArtifact(String)} or {@link #loadArtifact(String, int)} instead.
    */
+  @Deprecated
   public Maybe<Part> loadArtifact(String filename, Optional<Integer> version) {
     if (invocationContext.artifactService() == null) {
       throw new IllegalStateException("Artifact service is not initialized.");

core/src/main/java/com/google/adk/artifacts/BaseArtifactService.java

@@ -55,22 +55,26 @@ Single<Integer> saveArtifact(
   default Single<Part> saveAndReloadArtifact(
       String appName, String userId, String sessionId, String filename, Part artifact) {
     return saveArtifact(appName, userId, sessionId, filename, artifact)
-        .flatMap(
-            version ->
-                loadArtifact(appName, userId, sessionId, filename, Optional.of(version))
-                    .toSingle());
+        .flatMap(version -> loadArtifact(appName, userId, sessionId, filename, version).toSingle());
+  }
+
+  /** Loads the latest version of an artifact from the service. */
+  default Maybe<Part> loadArtifact(
+      String appName, String userId, String sessionId, String filename) {
+    return loadArtifact(appName, userId, sessionId, filename, Optional.empty());
+  }
+
+  /** Loads a specific version of an artifact from the service. */
+  default Maybe<Part> loadArtifact(
+      String appName, String userId, String sessionId, String filename, int version) {
+    return loadArtifact(appName, userId, sessionId, filename, Optional.of(version));
   }
 
   /**
-   * Gets an artifact.
-   *
-   * @param appName the app name
-   * @param userId the user ID
-   * @param sessionId the session ID
-   * @param filename the filename
-   * @param version Optional version number. If null, loads the latest version.
-   * @return the artifact or empty if not found
+   * @deprecated Use {@link #loadArtifact(String, String, String, String)} or {@link
+   *     #loadArtifact(String, String, String, String, int)} instead.
    */
+  @Deprecated
   Maybe<Part> loadArtifact(
       String appName, String userId, String sessionId, String filename, Optional<Integer> version);
 

core/src/main/java/com/google/adk/artifacts/InMemoryArtifactService.java

@@ -129,10 +129,7 @@ public Single<ImmutableList<Integer>> listVersions(
   public Single<Part> saveAndReloadArtifact(
       String appName, String userId, String sessionId, String filename, Part artifact) {
     return saveArtifact(appName, userId, sessionId, filename, artifact)
-        .flatMap(
-            version ->
-                loadArtifact(appName, userId, sessionId, filename, Optional.of(version))
-                    .toSingle());
+        .flatMap(version -> loadArtifact(appName, userId, sessionId, filename, version).toSingle());
   }
 
   private Map<String, List<Part>> getArtifactsMap(String appName, String userId, String sessionId) {