test(integ-test): add CalcitePPLDashboardPatternsIT pinning BRAIN-label dashboard query

OpenSearch Dashboards renders BRAIN-pattern panels with the shape:

  patterns ... method=BRAIN mode=label
  | stats count() as pattern_count, take(message, 1) as sample_logs
    by patterns_field
  | sort -pattern_count
  | fields patterns_field, pattern_count, sample_logs

This integration test pins that shape on the analytics-engine route so
regressions surface immediately. Schema-only assertions because BRAIN's
clustering output is dataset-version-sensitive — the contract we care about
is "the query plans, executes, and returns three columns in the right order".

Currently red end-to-end pending the BRAIN label window-UDF type-cascade
fix (see the OpenSearch-side WIP commit "BRAIN window UDF + dashboard
query path scaffolding" — the {@code PplWindowCallRewriter} stub
documents the remaining gap).

Signed-off-by: Kai Huang <ahkcs@amazon.com>

Author: ahkcs

integ-test/src/test/java/org/opensearch/sql/calcite/remote/CalcitePPLDashboardPatternsIT.java

@@ -0,0 +1,74 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.sql.calcite.remote;
+
+import static org.opensearch.sql.legacy.TestsConstants.TEST_INDEX_HDFS_LOGS;
+import static org.opensearch.sql.util.MatcherUtils.schema;
+import static org.opensearch.sql.util.MatcherUtils.verifySchemaInOrder;
+
+import java.io.IOException;
+import org.json.JSONObject;
+import org.junit.Test;
+import org.opensearch.sql.ppl.PPLIntegTestCase;
+
+/**
+ * Pins the exact PPL query shape OpenSearch Dashboards uses to render BRAIN-pattern
+ * panels: {@code patterns ... method=BRAIN mode=label} followed by
+ * {@code stats count(), take(message, 1) by patterns_field | sort -pattern_count |
+ * fields patterns_field, pattern_count, sample_logs}.
+ *
+ * <p>The combination exercises three pieces that all have to be wired through the
+ * analytics-engine route together:
+ *
+ * <ul>
+ *   <li>{@code INTERNAL_PATTERN} as a window function (label mode emits one
+ *       matched wildcard pattern per row, broadcast across the partition).</li>
+ *   <li>{@code take(field, n)} aggregate to capture a representative sample log
+ *       per discovered pattern group.</li>
+ *   <li>{@code count()} aggregate + {@code sort} on the result.</li>
+ * </ul>
+ *
+ * <p>Schema-only assertions: BRAIN's clustering depends on a corpus large enough
+ * that the default heuristics fire, so per-row pattern strings are sensitive to
+ * dataset version. The schema check guarantees the query plans, executes, and
+ * returns the dashboard's three expected columns in the right order.
+ *
+ * @opensearch.internal
+ */
+public class CalcitePPLDashboardPatternsIT extends PPLIntegTestCase {
+  @Override
+  public void init() throws Exception {
+    super.init();
+    enableCalcite();
+    loadIndex(Index.HDFS_LOGS);
+  }
+
+  /**
+   * Mirrors the canonical Dashboards BRAIN-label pattern panel query. Unfiltered
+   * variant — pins the end-to-end plan compiles and returns the dashboard's
+   * three-column shape (matched wildcard pattern + occurrence count + sample log).
+   */
+  @Test
+  public void testDashboardBrainLabelStatsByPatternsField() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format(
+                "source=%s"
+                    + " | patterns content method=BRAIN mode=label"
+                    + "   max_sample_count=5 variable_count_threshold=5"
+                    + "   frequency_threshold_percentage=0.2"
+                    + " | stats count() as pattern_count, take(content, 1) as sample_logs"
+                    + "   by patterns_field"
+                    + " | sort - pattern_count"
+                    + " | fields patterns_field, pattern_count, sample_logs",
+                TEST_INDEX_HDFS_LOGS));
+    verifySchemaInOrder(
+        result,
+        schema("patterns_field", "string"),
+        schema("pattern_count", "bigint"),
+        schema("sample_logs", "array"));
+  }
+}