fix(grid): include nested sub-groups when exporting pivot breakdown to CSV in GridGroupingsEngine

lib/features/workspace/grid_groupings_engine.dart

@@ -218,20 +218,38 @@ abstract final class GridGroupingsEngine {
     }
   }
 
-  /// Exports pivot summary to CSV format.
+  /// Exports pivot summary to CSV format, recursively including nested sub-groups.
   static String exportPivotToCsv({
     required List<GroupedCategory> groups,
     required String groupByColumnName,
     GroupAggregationConfig aggConfig = const GroupAggregationConfig(),
+    bool useCompoundKeys = false,
   }) {
     final buffer = StringBuffer();
     buffer.writeln('Group Key,Count,Percentage,Aggregate');
 
-    for (final g in groups) {
+    void writeCategory(GroupedCategory g, [String parentPath = '']) {
       final aggStr = g.aggValue != null ? g.aggValue!.toStringAsFixed(2) : '-';
+      final String keyText;
+      if (useCompoundKeys && parentPath.isNotEmpty) {
+        keyText = '$parentPath > ${g.groupKey}';
+      } else {
+        final indent = '  ' * g.level;
+        keyText = '$indent${g.groupKey}';
+      }
+      final escapedKey = keyText.replaceAll('"', '""');
       buffer.writeln(
-        '"${g.groupKey.replaceAll('"', '""')}",${g.count},${g.percentage.toStringAsFixed(2)}%,$aggStr',
+        '"$escapedKey",${g.count},${g.percentage.toStringAsFixed(2)}%,$aggStr',
       );
+
+      for (final sub in g.subGroups) {
+        final nextParent = parentPath.isEmpty ? g.groupKey : '$parentPath > ${g.groupKey}';
+        writeCategory(sub, nextParent);
+      }
+    }
+
+    for (final g in groups) {
+      writeCategory(g);
     }
 
     return buffer.toString();

test/features/workspace/data_grid_engines_test.dart

@@ -312,5 +312,49 @@ void main() {
       expect(csv, contains('Group Key,Count,Percentage,Aggregate'));
       expect(csv, contains('"ACTIVE",3,60.00%,600.00'));
     });
+
+    test('exports multi-level hierarchical pivot table to CSV with nested sub-groups', () {
+      final multiLevelRows = [
+        ['USA', 'NY', '100'],
+        ['USA', 'CA', '200'],
+        ['UK', 'London', '300'],
+      ];
+
+      final groups = GridGroupingsEngine.buildGroups(
+        groupColIndices: [0, 1],
+        rows: multiLevelRows,
+        aggConfig: const GroupAggregationConfig(
+          aggType: GroupingAggType.sum,
+          targetColIndex: 2,
+        ),
+      );
+
+      expect(groups.first.hasSubGroups, isTrue);
+
+      // Default indented export
+      final csvIndented = GridGroupingsEngine.exportPivotToCsv(
+        groups: groups,
+        groupByColumnName: 'Country',
+      );
+
+      expect(csvIndented, contains('"USA",2,66.67%,300.00'));
+      expect(csvIndented, contains('"  CA",1,33.33%,200.00'));
+      expect(csvIndented, contains('"  NY",1,33.33%,100.00'));
+      expect(csvIndented, contains('"UK",1,33.33%,300.00'));
+      expect(csvIndented, contains('"  London",1,33.33%,300.00'));
+
+      // Compound keys export
+      final csvCompound = GridGroupingsEngine.exportPivotToCsv(
+        groups: groups,
+        groupByColumnName: 'Country',
+        useCompoundKeys: true,
+      );
+
+      expect(csvCompound, contains('"USA",2,66.67%,300.00'));
+      expect(csvCompound, contains('"USA > CA",1,33.33%,200.00'));
+      expect(csvCompound, contains('"USA > NY",1,33.33%,100.00'));
+      expect(csvCompound, contains('"UK",1,33.33%,300.00'));
+      expect(csvCompound, contains('"UK > London",1,33.33%,300.00'));
+    });
   });
 }