Enable only in snapshot builds for now

Author: smalyshev

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/action/EsqlCapabilities.java

@@ -1190,7 +1190,7 @@ public enum Cap {
         /**
          * Enable support for cross-cluster lookup joins.
          */
-        ENABLE_LOOKUP_JOIN_ON_REMOTE,
+        ENABLE_LOOKUP_JOIN_ON_REMOTE(Build.current().isSnapshot()),
 
         /**
          * MATCH PHRASE function

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/parser/LogicalPlanBuilder.java

@@ -90,7 +90,6 @@
 import java.util.function.Function;
 
 import static java.util.Collections.emptyList;
-import static org.elasticsearch.xpack.esql.common.Failure.fail;
 import static org.elasticsearch.xpack.esql.core.type.DataType.KEYWORD;
 import static org.elasticsearch.xpack.esql.core.util.StringUtils.WILDCARD;
 import static org.elasticsearch.xpack.esql.expression.NamedExpressions.mergeOutputExpressions;
@@ -642,6 +641,9 @@ public PlanFactory visitJoinCommand(EsqlBaseParser.JoinCommandContext ctx) {
                     return false;
                 }
             });
+            if (hasRemotes && EsqlCapabilities.Cap.ENABLE_LOOKUP_JOIN_ON_REMOTE.isEnabled() == false) {
+                throw new ParsingException(source, "remote clusters are not supported with LOOKUP JOIN");
+            }
             return new LookupJoin(source, p, right, joinFields, hasRemotes);
         };
     }