[ES|QL] Modify GenerativeMetrics test and unmute (#136932)

This commit modifies the GenerativeMetrics test to avoid certain
illegal queries, adds a few more allowed error messages, and
unmutes the test in general.

Author: limotova

muted-tests.yml

@@ -429,9 +429,6 @@ tests:
 - class: org.elasticsearch.xpack.esql.qa.mixed.MixedClusterEsqlSpecIT
   method: test {csv-spec:stats.CountDistinctWithConditions}
   issue: https://github.com/elastic/elasticsearch/issues/134993
-- class: org.elasticsearch.xpack.esql.qa.single_node.GenerativeMetricsIT
-  method: test
-  issue: https://github.com/elastic/elasticsearch/issues/135055
 - class: org.elasticsearch.xpack.esql.heap_attack.HeapAttackIT
   method: testLookupExplosionBigString
   issue: https://github.com/elastic/elasticsearch/issues/135122

x-pack/plugin/esql/qa/server/src/main/java/org/elasticsearch/xpack/esql/qa/rest/generative/GenerativeRestTest.java

@@ -81,7 +81,9 @@ public abstract class GenerativeRestTest extends ESRestTestCase implements Query
         "time-series.*the first aggregation.*is not allowed",
         "count_star .* can't be used with TS command",
         "time_series aggregate.* can only be used with the TS command",
-        "implicit time-series aggregation function .* doesn't support type .*"
+        "implicit time-series aggregation function .* doesn't support type .*",
+        "INLINE STATS .* can only be used after STATS when used with TS command",
+        "cannot group by a metric field .* in a time-series aggregation"
     );
 
     public static final Set<Pattern> ALLOWED_ERROR_PATTERNS = ALLOWED_ERRORS.stream()

x-pack/plugin/esql/qa/testFixtures/src/main/java/org/elasticsearch/xpack/esql/generator/EsqlQueryGenerator.java

@@ -133,28 +133,24 @@ public static void generatePipeline(
             if (executor.currentSchema().isEmpty()) {
                 break;
             }
-            boolean commandAllowed = false;
-            while (commandAllowed == false) {
-                commandGenerator = isTimeSeries && canGenerateTimeSeries
-                    ? randomMetricsPipeCommandGenerator()
-                    : randomPipeCommandGenerator();
-                if (isTimeSeries == false) {
-                    commandAllowed = true;
-                } else {
-                    if (commandGenerator.equals(TimeSeriesStatsGenerator.INSTANCE) || commandGenerator.equals(StatsGenerator.INSTANCE)) {
-                        if (canGenerateTimeSeries) {
-                            canGenerateTimeSeries = false;
-                            commandAllowed = true;
-                        }
-                    } else if (commandGenerator.equals(RenameGenerator.INSTANCE)) {
-                        // https://github.com/elastic/elasticsearch/issues/134994
-                        canGenerateTimeSeries = false;
-                        commandAllowed = true;
-                    } else {
-                        commandAllowed = true;
+            commandGenerator = isTimeSeries && canGenerateTimeSeries ? randomMetricsPipeCommandGenerator() : randomPipeCommandGenerator();
+            if (isTimeSeries) {
+                if (commandGenerator.equals(ForkGenerator.INSTANCE)) {
+                    // don't fork with TS command until this is resolved: https://github.com/elastic/elasticsearch/issues/136927
+                    continue;
+                }
+                if (commandGenerator.equals(TimeSeriesStatsGenerator.INSTANCE) || commandGenerator.equals(StatsGenerator.INSTANCE)) {
+                    if (canGenerateTimeSeries == false) {
+                        // Don't generate multiple stats commands in a single query for TS
+                        continue;
                     }
+                    canGenerateTimeSeries = false;
+                } else if (commandGenerator.equals(RenameGenerator.INSTANCE)) {
+                    // don't allow stats after a rename until this is resolved: https://github.com/elastic/elasticsearch/issues/134994
+                    canGenerateTimeSeries = false;
                 }
             }
+
             desc = commandGenerator.generate(executor.previousCommands(), executor.currentSchema(), schema, queryExecutor);
             if (desc == CommandGenerator.EMPTY_DESCRIPTION) {
                 continue;