[Enhancement] Classify unsupported-feature errors as client errors (4xx) on the SQL path (#5569)

Signed-off-by: Jialiang Liang <jiallian@amazon.com>

Author: RyanL1997

api/src/main/java/org/opensearch/sql/api/UnifiedQueryPlanner.java

@@ -27,6 +27,7 @@
 import org.opensearch.sql.calcite.CalciteRelNodeVisitor;
 import org.opensearch.sql.common.antlr.SyntaxCheckException;
 import org.opensearch.sql.common.error.ErrorReport;
+import org.opensearch.sql.exception.CalciteUnsupportedException;
 import org.opensearch.sql.exception.QueryEngineException;
 import org.opensearch.sql.exception.SemanticCheckException;
 
@@ -73,6 +74,10 @@ public RelNode plan(String query) {
             }
             return plan;
           });
+    } catch (CalciteUnsupportedException e) {
+      // Unsupported feature (e.g. table functions) is an invalid query, i.e. a client error.
+      // Must precede the QueryEngineException branch as it is a subclass.
+      throw new SemanticCheckException(e.getMessage(), e);
     } catch (SyntaxCheckException
         | QueryEngineException
         | UnsupportedOperationException

api/src/test/java/org/opensearch/sql/api/UnifiedQueryPlannerTest.java

@@ -16,6 +16,7 @@
 import org.junit.Test;
 import org.opensearch.sql.common.antlr.SyntaxCheckException;
 import org.opensearch.sql.common.error.ErrorReport;
+import org.opensearch.sql.exception.CalciteUnsupportedException;
 import org.opensearch.sql.exception.SemanticCheckException;
 import org.opensearch.sql.executor.QueryType;
 
@@ -147,6 +148,17 @@ public void invalidTableIsRethrownAsSemanticCheckException() {
         .assertCauseType(CalciteException.class);
   }
 
+  @Test
+  public void unsupportedFeatureIsRethrownAsSemanticCheckException() {
+    // A feature unsupported on the analytics engine (here a PPL command that raises
+    // CalciteUnsupportedException; SQL table functions like vectorSearch() take the same path) is
+    // an invalid query, normalized to a SemanticCheckException so callers classify it as a 4xx.
+    givenInvalidQuery("source = catalog.employees | kmeans")
+        .assertErrorType(SemanticCheckException.class)
+        .assertCauseType(CalciteUnsupportedException.class)
+        .assertErrorMessageContains("unsupported in Calcite");
+  }
+
   @Test
   public void assertionErrorIsWrappedAsSemanticCheckException() {
     // Remove when the underlying Calcite assertion is fixed.