address review comments

docs/reference/mapping/types/sparse-vector.asciidoc

@@ -33,11 +33,15 @@ The following parameters are accepted by `sparse_vector` fields:
 
 [horizontal]
 
-<<mapping-store,`store`>>::
-
-    Whether the field value should be stored and retrievable separately from
-    the <<mapping-source-field,`_source`>> field. Accepts `true` or `false`
-    (default).
+<<mapping-store,store>>::
+
+Indicates whether the field value should be stored and retrievable independently of the <<mapping-source-field,_source>> field.
+Accepted values: true or false (default).
+The field's data is stored using term vectors, a disk-efficient structure compared to the original JSON input.
+The input map can be retrieved during a search request via the <<search-fields-param,`fields` parameter>>.
+To benefit from reduced disk usage, you must either:
+  * Exclude the field from <<source-filtering, _source>>.
+  * Use <<synthetic-source,synthetic `_source`>>.
 
 [[index-multi-value-sparse-vectors]]
 ==== Multi-value sparse vectors

server/src/main/java/org/elasticsearch/index/mapper/MapperFeatures.java

@@ -25,7 +25,6 @@ public class MapperFeatures implements FeatureSpecification {
     // Used to avoid noise in mixed cluster and rest compatibility tests. Must not be backported to 8.x branch.
     // This label gets added to tests with such failures before merging with main, then removed when backported to 8.x.
     public static final NodeFeature BWC_WORKAROUND_9_0 = new NodeFeature("mapper.bwc_workaround_9_0");
-    public static final NodeFeature SPARSE_VECTOR_STORE_SUPPORT = new NodeFeature("mapper.sparse_vector.store_support");
 
     @Override
     public Set<NodeFeature> getFeatures() {
@@ -76,8 +75,7 @@ public Set<NodeFeature> getTestFeatures() {
             MapperService.LOGSDB_DEFAULT_IGNORE_DYNAMIC_BEYOND_LIMIT,
             DocumentParser.FIX_PARSING_SUBOBJECTS_FALSE_DYNAMIC_FALSE,
             CONSTANT_KEYWORD_SYNTHETIC_SOURCE_WRITE_FIX,
-            META_FETCH_FIELDS_ERROR_CODE_CHANGED,
-            SPARSE_VECTOR_STORE_SUPPORT
+            META_FETCH_FIELDS_ERROR_CODE_CHANGED
         );
     }
 }

server/src/main/java/org/elasticsearch/index/mapper/vectors/SparseVectorFieldMapper.java

@@ -22,6 +22,7 @@
 import org.apache.lucene.util.BytesRef;
 import org.elasticsearch.common.logging.DeprecationCategory;
 import org.elasticsearch.common.lucene.Lucene;
+import org.elasticsearch.features.NodeFeature;
 import org.elasticsearch.index.IndexVersion;
 import org.elasticsearch.index.IndexVersions;
 import org.elasticsearch.index.analysis.NamedAnalyzer;
@@ -58,6 +59,8 @@ public class SparseVectorFieldMapper extends FieldMapper {
 
     public static final String CONTENT_TYPE = "sparse_vector";
 
+    public static final NodeFeature SPARSE_VECTOR_STORE_SUPPORT = new NodeFeature("mapper.sparse_vector.store_support");
+
     static final String ERROR_MESSAGE_7X = "[sparse_vector] field type in old 7.x indices is allowed to "
         + "contain [sparse_vector] fields, but they cannot be indexed or searched.";
     static final String ERROR_MESSAGE_8X = "The [sparse_vector] field type is not supported on indices created on versions 8.0 to 8.10.";

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/XPackFeatures.java

@@ -9,6 +9,7 @@
 
 import org.elasticsearch.features.FeatureSpecification;
 import org.elasticsearch.features.NodeFeature;
+import org.elasticsearch.index.mapper.vectors.SparseVectorFieldMapper;
 import org.elasticsearch.license.License;
 import org.elasticsearch.xpack.core.datatiers.NodesDataTiersUsageTransportAction;
 
@@ -30,4 +31,9 @@ public Set<NodeFeature> getFeatures() {
             LOGSDB_TELMETRY_STATS
         );
     }
+
+    @Override
+    public Set<NodeFeature> getTestFeatures() {
+        return Set.of(SparseVectorFieldMapper.SPARSE_VECTOR_STORE_SUPPORT);
+    }
 }