[Inference API] Improve chunked results error message (#115807) (#115978)

* Improve chunked results error message

* Update RestStatus to conflict

* precommit

* Update docs/changelog/115807.yaml

(cherry picked from commit 6742147d6ada3af42ff73f03eb45fd2486cb64cc)

docs/changelog/115807.yaml

@@ -0,0 +1,5 @@
+pr: 115807
+summary: "[Inference API] Improve chunked results error message"
+area: Machine Learning
+type: enhancement
+issues: []

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/inference/results/ResultUtils.java

@@ -14,8 +14,9 @@ public class ResultUtils {
 
     public static ElasticsearchStatusException createInvalidChunkedResultException(String expectedResultName, String receivedResultName) {
         return new ElasticsearchStatusException(
-            "Expected a chunked inference [{}] received [{}]",
-            RestStatus.INTERNAL_SERVER_ERROR,
+            "Received incompatible results. Check that your model_id matches the task_type of this endpoint. "
+                + "Expected chunked output of type [{}] but received [{}].",
+            RestStatus.CONFLICT,
             expectedResultName,
             receivedResultName
         );