Fix regression introduced during tests.

Author: afoucret

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/external/http/sender/RequestExecutorService.java

@@ -305,12 +305,12 @@ private void executeTaskImmediately(RejectableTask task) {
                 e
             );
 
-            task.onRejection(
-                new EsRejectedExecutionException(
-                    format("Failed to execute request for inference id [%s]", task.getRequestManager().inferenceEntityId()),
-                    false
-                )
+            var rejectionException = new EsRejectedExecutionException(
+                format("Failed to execute request for inference id [%s]", task.getRequestManager().inferenceEntityId()),
+                false
             );
+            rejectionException.initCause(e);
+            task.onRejection(rejectionException);
         }
     }
 

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/services/elastic/ElasticInferenceService.java

@@ -39,6 +39,7 @@
 import org.elasticsearch.xpack.core.inference.results.ChunkedInferenceError;
 import org.elasticsearch.xpack.core.inference.results.SparseEmbeddingResults;
 import org.elasticsearch.xpack.core.ml.inference.results.ErrorInferenceResults;
+import org.elasticsearch.xpack.inference.external.http.sender.ChatCompletionInput;
 import org.elasticsearch.xpack.inference.external.http.sender.EmbeddingsInput;
 import org.elasticsearch.xpack.inference.external.http.sender.HttpRequestSender;
 import org.elasticsearch.xpack.inference.external.http.sender.InferenceInputs;
@@ -72,6 +73,7 @@
 import static org.elasticsearch.xpack.inference.services.ServiceUtils.removeFromMapOrThrowIfNull;
 import static org.elasticsearch.xpack.inference.services.ServiceUtils.throwIfNotEmptyMap;
 import static org.elasticsearch.xpack.inference.services.ServiceUtils.useChatCompletionUrlMessage;
+import static org.elasticsearch.xpack.inference.services.openai.action.OpenAiActionCreator.USER_ROLE;
 
 public class ElasticInferenceService extends SenderService {
 
@@ -164,7 +166,8 @@ protected void doUnifiedCompletionInfer(
         TimeValue timeout,
         ActionListener<InferenceServiceResults> listener
     ) {
-        if (model instanceof ElasticInferenceServiceCompletionModel == false || model.getTaskType() != TaskType.CHAT_COMPLETION) {
+        if (model instanceof ElasticInferenceServiceCompletionModel == false
+            || (model.getTaskType() != TaskType.CHAT_COMPLETION && model.getTaskType() != TaskType.COMPLETION)) {
             listener.onFailure(createInvalidModelException(model));
             return;
         }
@@ -214,10 +217,17 @@ protected void doInfer(
 
         var elasticInferenceServiceModel = (ElasticInferenceServiceModel) model;
 
+        // For ElasticInferenceServiceCompletionModel, convert ChatCompletionInput to UnifiedChatInput
+        // since the request manager expects UnifiedChatInput
+        final InferenceInputs finalInputs = (elasticInferenceServiceModel instanceof ElasticInferenceServiceCompletionModel
+            && inputs instanceof ChatCompletionInput)
+                ? new UnifiedChatInput((ChatCompletionInput) inputs, USER_ROLE)
+                : inputs;
+
         actionCreator.create(
             elasticInferenceServiceModel,
             currentTraceInfo,
-            listener.delegateFailureAndWrap((delegate, action) -> action.execute(inputs, timeout, delegate))
+            listener.delegateFailureAndWrap((delegate, action) -> action.execute(finalInputs, timeout, delegate))
         );
     }