Fix deserialization with custom addition

- try-catch based approach on Subtype annotation mentions
- Also pass custom list of candidates

Author: rpanackal

orchestration/src/main/java/com/sap/ai/sdk/orchestration/JacksonMixins.java

@@ -18,4 +18,8 @@ interface LLMModuleResultMixIn {}
   @JsonTypeInfo(use = JsonTypeInfo.Id.NONE)
   @JsonDeserialize(as = LLMChoice.class)
   interface ModuleResultsOutputUnmaskingInnerMixIn {}
+
+  @JsonTypeInfo(use = JsonTypeInfo.Id.NONE)
+  interface NoneTypeInfoMixin {}
+  
 }

orchestration/src/main/java/com/sap/ai/sdk/orchestration/OrchestrationClient.java

@@ -5,11 +5,13 @@
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.module.SimpleModule;
 import com.fasterxml.jackson.databind.node.ObjectNode;
 import com.google.common.annotations.Beta;
 import com.sap.ai.sdk.core.AiCoreService;
 import com.sap.ai.sdk.core.DeploymentResolutionException;
 import com.sap.ai.sdk.core.commons.ClientResponseHandler;
+import com.sap.ai.sdk.orchestration.model.ChatMessagesInner;
 import com.sap.ai.sdk.orchestration.model.CompletionPostRequest;
 import com.sap.ai.sdk.orchestration.model.CompletionPostResponse;
 import com.sap.ai.sdk.orchestration.model.LLMModuleResult;
@@ -47,6 +49,14 @@ public class OrchestrationClient {
     JACKSON.addMixIn(
         ModuleResultsOutputUnmaskingInner.class,
         JacksonMixins.ModuleResultsOutputUnmaskingInnerMixIn.class);
+
+    var module =
+        new SimpleModule()
+            .addDeserializer(
+                ChatMessagesInner.class,
+                new PolymorphicFallbackDeserializer<>(ChatMessagesInner.class))
+            .setMixInAnnotation(ChatMessagesInner.class, JacksonMixins.NoneTypeInfoMixin.class);
+    JACKSON.registerModule(module);
   }
 
   @Nonnull private final Supplier<HttpDestination> destinationSupplier;

orchestration/src/main/java/com/sap/ai/sdk/orchestration/PolymorphicFallbackDeserializer.java

@@ -0,0 +1,87 @@
+package com.sap.ai.sdk.orchestration;
+
+import com.fasterxml.jackson.annotation.JsonSubTypes;
+import com.fasterxml.jackson.core.JsonParser;
+import com.fasterxml.jackson.databind.DeserializationContext;
+import com.fasterxml.jackson.databind.JsonMappingException;
+import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Handles polymorphic deserialization for a base class or interface.
+ *
+ * <p>This deserializer attempts to deserialize JSON into a subtype of a base class or interface.
+ * Subtypes are either discovered using the {@link JsonSubTypes} annotation or provided explicitly.
+ * If deserialization fails for all candidates, a {@link JsonMappingException} is thrown with
+ * suppressed exceptions.
+ *
+ * @param <T> The base type for deserialization.
+ */
+public class PolymorphicFallbackDeserializer<T> extends StdDeserializer<T> {
+
+  private final List<Class<? extends T>> candidates;
+
+  /**
+   * Constructs the deserializer using the {@link JsonSubTypes} annotation.
+   *
+   * @param baseClass The base class or interface to be resolved.
+   * @throws IllegalStateException If no subtypes are found.
+   */
+  protected PolymorphicFallbackDeserializer(Class<T> baseClass) {
+    super(baseClass);
+
+    final var subTypes = baseClass.getAnnotation(JsonSubTypes.class);
+    if (subTypes == null || subTypes.value().length == 0) {
+      throw new IllegalStateException("No subtypes found for " + baseClass.getName());
+    }
+
+    candidates = new ArrayList<>();
+    for (final var subType : subTypes.value()) {
+      candidates.add((Class<? extends T>) subType.value());
+    }
+  }
+
+  /**
+   * Constructs the deserializer with an explicit list of candidate types.
+   *
+   * @param baseClass The base class or interface to be resolved.
+   * @param candidates A list of candidate classes to try deserialization.
+   */
+  protected PolymorphicFallbackDeserializer(
+      Class<T> baseClass, List<Class<? extends T>> candidates) {
+    super(baseClass);
+    this.candidates = candidates;
+  }
+
+  /**
+   * Deserializes the JSON into the first matching candidate type.
+   *
+   * @param jsonParser The parser providing the JSON.
+   * @param deserializationContext The deserialization context.
+   * @return The deserialized object of a matching candidate type.
+   * @throws JsonMappingException If deserialization fails for all candidates.
+   * @throws IOException If an I/O error occurs.
+   */
+  @Override
+  public T deserialize(JsonParser jsonParser, DeserializationContext deserializationContext)
+      throws IOException {
+
+    final var root = jsonParser.readValueAsTree();
+    final var throwable =
+        JsonMappingException.from(
+            jsonParser,
+            "PolymorphicFallbackDeserializer failed to deserialize " + handledType().getName());
+
+    for (final var candidate : candidates) {
+      try {
+        return jsonParser.getCodec().treeToValue(root, candidate);
+      } catch (JsonMappingException e) {
+        throwable.addSuppressed(e);
+      }
+    }
+
+    throw throwable;
+  }
+}