[ML] Fix model registry upgrade tests (#125774)

Author: davidkyle

muted-tests.yml

@@ -465,30 +465,12 @@ tests:
 - class: org.elasticsearch.qa.verify_version_constants.VerifyVersionConstantsIT
   method: testLuceneVersionConstant
   issue: https://github.com/elastic/elasticsearch/issues/125638
-- class: org.elasticsearch.xpack.application.HuggingFaceServiceUpgradeIT
-  method: testElser {upgradedNodes=2}
-  issue: https://github.com/elastic/elasticsearch/issues/125550
-- class: org.elasticsearch.xpack.application.HuggingFaceServiceUpgradeIT
-  method: testHFEmbeddings {upgradedNodes=3}
-  issue: https://github.com/elastic/elasticsearch/issues/125543
-- class: org.elasticsearch.xpack.application.HuggingFaceServiceUpgradeIT
-  method: testElser {upgradedNodes=3}
-  issue: https://github.com/elastic/elasticsearch/issues/125544
-- class: org.elasticsearch.xpack.application.ModelRegistryUpgradeIT
-  method: testUpgradeModels {upgradedNodes=3}
-  issue: https://github.com/elastic/elasticsearch/issues/125535
-- class: org.elasticsearch.xpack.application.ModelRegistryUpgradeIT
-  method: testUpgradeModels {upgradedNodes=0}
-  issue: https://github.com/elastic/elasticsearch/issues/125549
 - class: org.elasticsearch.xpack.esql.qa.mixed.MixedClusterEsqlSpecIT
   method: test {date.Implicit casting strings to dates for IN operator ASYNC}
   issue: https://github.com/elastic/elasticsearch/issues/121490
 - class: org.elasticsearch.packaging.test.DebPreservationTests
   method: test40RestartOnUpgrade
   issue: https://github.com/elastic/elasticsearch/issues/125821
-- class: org.elasticsearch.xpack.application.HuggingFaceServiceUpgradeIT
-  method: testHFEmbeddings {upgradedNodes=2}
-  issue: https://github.com/elastic/elasticsearch/issues/125551
 - class: org.elasticsearch.xpack.downsample.DataStreamLifecycleDownsampleDisruptionIT
   method: testDataStreamLifecycleDownsampleRollingRestart
   issue: https://github.com/elastic/elasticsearch/issues/123769

x-pack/plugin/inference/qa/rolling-upgrade/src/javaRestTest/java/org/elasticsearch/xpack/application/ModelRegistryUpgradeIT.java

@@ -9,9 +9,6 @@
 
 import com.carrotsearch.randomizedtesting.annotations.Name;
 
-import org.elasticsearch.common.Strings;
-import org.elasticsearch.index.mapper.vectors.DenseVectorFieldMapper;
-import org.elasticsearch.inference.SimilarityMeasure;
 import org.elasticsearch.inference.TaskType;
 import org.elasticsearch.test.http.MockResponse;
 import org.elasticsearch.test.http.MockWebServer;
@@ -25,6 +22,7 @@
 
 import static org.elasticsearch.xpack.application.HuggingFaceServiceUpgradeIT.elserConfig;
 import static org.elasticsearch.xpack.application.HuggingFaceServiceUpgradeIT.elserResponse;
+import static org.elasticsearch.xpack.application.HuggingFaceServiceUpgradeIT.embeddingConfig;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.greaterThan;
 
@@ -137,16 +135,4 @@ private String embeddingResponse(int numDimensions) {
         result.append("]]");
         return result.toString();
     }
-
-    static String embeddingConfig(String url) {
-        return Strings.format("""
-            {
-                "service": "hugging_face",
-                "service_settings": {
-                    "url": "%s",
-                    "api_key": "XXXX"
-                }
-            }
-            """, url, randomFrom(DenseVectorFieldMapper.ElementType.values()), randomFrom(SimilarityMeasure.values()));
-    }
 }

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/services/huggingface/HuggingFaceServiceSettings.java

@@ -188,7 +188,11 @@ public URI uri() {
 
     @Override
     public SimilarityMeasure similarity() {
-        return similarity;
+        // Default to cosine similarity if not set.
+        // Inference endpoints created before 8.15 may not have this set,
+        // after 8.15 the default is cosine similarity. Semantic text requires
+        // a non-null similarity measure
+        return similarity == null ? SimilarityMeasure.COSINE : similarity;
     }
 
     @Override