Add setContextClassLoader wrapper to QueryService Calcite paths

The analyze() and convertToCalcitePlan() steps in executeWithCalcite()
and explainWithCalcite() trigger RexSimplify which uses Janino for
constant folding. Without the context classloader set, UDF expressions
like SAFE_CAST('TRUE') can't be folded, causing explain plan differences
vs main branch. Adding the wrapper here covers the entire Calcite
lifecycle for both execute and explain paths.

Revert the separate boolean string literal YAML since all three boolean
tests now produce the same plan (SAFE_CAST folds correctly).

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

Author: ahkcs

core/src/main/java/org/opensearch/sql/executor/QueryService.java

@@ -139,14 +139,23 @@ public void executeWithCalcite(
                 QueryProfiling.activate(QueryContext.isProfileEnabled());
             ProfileMetric analyzeMetric = profileContext.getOrCreateMetric(MetricName.ANALYZE);
             long analyzeStart = System.nanoTime();
-            CalcitePlanContext context =
-                CalcitePlanContext.create(
-                    buildFrameworkConfig(), SysLimit.fromSettings(settings), queryType);
-            context.setHighlightConfig(highlightConfig);
-            RelNode relNode = analyze(plan, context);
-            RelNode calcitePlan = convertToCalcitePlan(relNode, context);
-            analyzeMetric.set(System.nanoTime() - analyzeStart);
-            executionEngine.execute(calcitePlan, context, listener);
+            // Set thread context classloader so patched Calcite (CALCITE-3745) uses the
+            // SQL plugin's classloader for Janino compilation during planning/execution.
+            Thread currentThread = Thread.currentThread();
+            ClassLoader originalCl = currentThread.getContextClassLoader();
+            currentThread.setContextClassLoader(QueryService.class.getClassLoader());
+            try {
+              CalcitePlanContext context =
+                  CalcitePlanContext.create(
+                      buildFrameworkConfig(), SysLimit.fromSettings(settings), queryType);
+              context.setHighlightConfig(highlightConfig);
+              RelNode relNode = analyze(plan, context);
+              RelNode calcitePlan = convertToCalcitePlan(relNode, context);
+              analyzeMetric.set(System.nanoTime() - analyzeStart);
+              executionEngine.execute(calcitePlan, context, listener);
+            } finally {
+              currentThread.setContextClassLoader(originalCl);
+            }
           } catch (Throwable t) {
             if (isCalciteFallbackAllowed(t) && !(t instanceof NonFallbackCalciteException)) {
               log.warn("Fallback to V2 query engine since got exception", t);
@@ -169,17 +178,26 @@ public void explainWithCalcite(
         () -> {
           try {
             QueryProfiling.noop();
-            CalcitePlanContext context =
-                CalcitePlanContext.create(
-                    buildFrameworkConfig(), SysLimit.fromSettings(settings), queryType);
-            context.setHighlightConfig(highlightConfig);
-            context.run(
-                () -> {
-                  RelNode relNode = analyze(plan, context);
-                  RelNode calcitePlan = convertToCalcitePlan(relNode, context);
-                  executionEngine.explain(calcitePlan, mode, context, listener);
-                },
-                settings);
+            // Set thread context classloader so patched Calcite (CALCITE-3745) uses the
+            // SQL plugin's classloader for Janino compilation during planning/execution.
+            Thread currentThread = Thread.currentThread();
+            ClassLoader originalCl = currentThread.getContextClassLoader();
+            currentThread.setContextClassLoader(QueryService.class.getClassLoader());
+            try {
+              CalcitePlanContext context =
+                  CalcitePlanContext.create(
+                      buildFrameworkConfig(), SysLimit.fromSettings(settings), queryType);
+              context.setHighlightConfig(highlightConfig);
+              context.run(
+                  () -> {
+                    RelNode relNode = analyze(plan, context);
+                    RelNode calcitePlan = convertToCalcitePlan(relNode, context);
+                    executionEngine.explain(calcitePlan, mode, context, listener);
+                  },
+                  settings);
+            } finally {
+              currentThread.setContextClassLoader(originalCl);
+            }
           } catch (Throwable t) {
             if (isCalciteFallbackAllowed(t)) {
               log.warn("Fallback to V2 query engine since got exception", t);

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

@@ -2735,14 +2735,13 @@ public void testFilterBooleanFieldWithTRUE() throws IOException {
   @Test
   public void testFilterBooleanFieldWithStringLiteral() throws IOException {
     enabledOnlyWhenPushdownIsEnabled();
-    // Test boolean field with string literal 'TRUE' - Calcite keeps SAFE_CAST in logical plan
-    // but still generates the same term query in physical plan
+    // Test boolean field with string literal 'TRUE' - Calcite converts to boolean true
+    // and generates same term query as boolean literal
     String query =
         StringUtils.format(
             "source=%s firstname=Amber | where male = 'TRUE' | fields firstname", TEST_INDEX_BANK);
     var result = explainQueryYaml(query);
-    String expected =
-        loadExpectedPlan("explain_filter_query_string_with_boolean_string_literal.yaml");
+    String expected = loadExpectedPlan("explain_filter_query_string_with_boolean.yaml");
     assertYamlEqualsIgnoreId(expected, result);
   }