Fix multi cluster tests to accept SET statements

Author: ivancea

x-pack/plugin/esql/qa/server/multi-clusters/src/javaRestTest/java/org/elasticsearch/xpack/esql/ccq/MultiClusterSpecIT.java

@@ -304,7 +304,15 @@ static CsvSpecReader.CsvTestCase convertToRemoteIndices(CsvSpecReader.CsvTestCas
         String first = commands[0].trim();
         // If true, we're using *:index, otherwise we're using *:index,index
         boolean onlyRemotes = canUseRemoteIndicesOnly() && randomBoolean();
-        String[] commandParts = first.split("\\s+", 2);
+
+        // Split "SET a=b; FROM x" into "SET a=b" and "FROM x"
+        int lastSetDelimiterPosition = first.lastIndexOf(';');
+        String setStatements = lastSetDelimiterPosition == -1 ? "" : first.substring(0, lastSetDelimiterPosition + 1);
+        String afterSetStatements = lastSetDelimiterPosition == -1 ? first : first.substring(lastSetDelimiterPosition + 1);
+
+        // Split "FROM a, b, c" into "FROM" and "a, b, c"
+        String[] commandParts = afterSetStatements.trim().split("\\s+", 2);
+
         String command = commandParts[0].trim();
         if (command.equalsIgnoreCase("from") || command.equalsIgnoreCase("ts")) {
             String[] indexMetadataParts = commandParts[1].split("(?i)\\bmetadata\\b", 2);
@@ -326,7 +334,7 @@ static CsvSpecReader.CsvTestCase convertToRemoteIndices(CsvSpecReader.CsvTestCas
                     + remoteIndices
                     + " "
                     + (indexMetadataParts.length == 1 ? "" : "metadata " + indexMetadataParts[1]);
-                testCase.query = newFirstCommand + query.substring(first.length());
+                testCase.query = setStatements + newFirstCommand + query.substring(first.length());
             }
         }