perf(workspace): harden memory lifecycle, staging buffer disposal, and grid row cache cleanup

lib/features/extensions/extension_table_view.dart

@@ -124,13 +124,16 @@ class _ExtensionTableViewState extends material.State<ExtensionTableView> {
       _totalRows = null;
       _filterController.clear();
       _filterActive = false;
+      _stagingBuffer?.dispose();
       _stagingBuffer = null;
       unawaited(_loadPage(refreshCount: true));
     }
   }
 
   @override
   void dispose() {
+    _stagingBuffer?.dispose();
+    _stagingBuffer = null;
     _filterController.dispose();
     super.dispose();
   }
@@ -208,6 +211,7 @@ class _ExtensionTableViewState extends material.State<ExtensionTableView> {
         _columns = dataResult.columns;
         _rows = dataResult.rows;
         _loading = false;
+        _stagingBuffer?.dispose();
         if (!widget.isView && (_capabilities?.supportsMutations == true)) {
           _stagingBuffer =
               DataGridStagingBuffer(columns: _columns, rows: _rows);

lib/features/mysql/mysql_sql_workspace.dart

@@ -149,6 +149,8 @@ class _MysqlSqlWorkspaceState extends material.State<MysqlSqlWorkspace> {
       );
     }
     _lease?.release();
+    _stagingBuffer?.dispose();
+    _stagingBuffer = null;
     _sqlController.dispose();
     super.dispose();
   }
@@ -244,6 +246,7 @@ class _MysqlSqlWorkspaceState extends material.State<MysqlSqlWorkspace> {
         _rows = outRows;
         _affectedRows = affected;
         _lastExecutedSql = userSql;
+        _stagingBuffer?.dispose();
         _stagingBuffer = cols.isNotEmpty
             ? DataGridStagingBuffer(columns: cols, rows: outRows)
             : null;
@@ -325,8 +328,10 @@ class _MysqlSqlWorkspaceState extends material.State<MysqlSqlWorkspace> {
       }
 
       if (!mounted) return;
+      final newRows = _stagingBuffer!.effectiveRows;
+      _stagingBuffer?.dispose();
       setState(() {
-        _rows = _stagingBuffer!.effectiveRows;
+        _rows = newRows;
         _stagingBuffer = DataGridStagingBuffer(columns: _columns, rows: _rows);
         _savingChanges = false;
       });

lib/features/postgresql/postgres_sql_workspace.dart

@@ -296,6 +296,8 @@ class _PostgresSqlWorkspaceState extends material.State<PostgresSqlWorkspace> {
       );
     }
     _dropLease();
+    _stagingBuffer?.dispose();
+    _stagingBuffer = null;
     _sqlController.dispose();
     super.dispose();
   }
@@ -388,6 +390,7 @@ class _PostgresSqlWorkspaceState extends material.State<PostgresSqlWorkspace> {
         _rows = outRows;
         _affectedRows = result.affectedRows;
         _lastExecutedSql = userSql;
+        _stagingBuffer?.dispose();
         _stagingBuffer = cols.isNotEmpty
             ? DataGridStagingBuffer(columns: cols, rows: outRows)
             : null;
@@ -478,8 +481,10 @@ class _PostgresSqlWorkspaceState extends material.State<PostgresSqlWorkspace> {
       await conn.execute(txSql, timeout: to);
 
       if (!mounted) return;
+      final newRows = _stagingBuffer!.effectiveRows;
+      _stagingBuffer?.dispose();
       setState(() {
-        _rows = _stagingBuffer!.effectiveRows;
+        _rows = newRows;
         _stagingBuffer = DataGridStagingBuffer(columns: _columns, rows: _rows);
         _savingChanges = false;
       });

lib/features/sqlite/sqlite_sql_workspace.dart

@@ -125,6 +125,8 @@ class _SqliteSqlWorkspaceState extends material.State<SqliteSqlWorkspace> {
         .removeListener(_appSettingsListener);
     _topFraction.dispose();
     _lease?.release();
+    _stagingBuffer?.dispose();
+    _stagingBuffer = null;
     _sqlController.dispose();
     super.dispose();
   }
@@ -206,6 +208,7 @@ class _SqliteSqlWorkspaceState extends material.State<SqliteSqlWorkspace> {
         _rows = outRows;
         _affectedRows = null;
         _lastExecutedSql = userSql;
+        _stagingBuffer?.dispose();
         _stagingBuffer = cols.isNotEmpty
             ? DataGridStagingBuffer(columns: cols, rows: outRows)
             : null;
@@ -285,8 +288,10 @@ class _SqliteSqlWorkspaceState extends material.State<SqliteSqlWorkspace> {
       }
 
       if (!mounted) return;
+      final newRows = _stagingBuffer!.effectiveRows;
+      _stagingBuffer?.dispose();
       setState(() {
-        _rows = _stagingBuffer!.effectiveRows;
+        _rows = newRows;
         _stagingBuffer = DataGridStagingBuffer(columns: _columns, rows: _rows);
         _savingChanges = false;
       });

lib/features/workspace/data_grid_staging_buffer.dart

@@ -315,5 +315,13 @@ class DataGridStagingBuffer extends ChangeNotifier {
     }
     return result;
   }
+
+  @override
+  void dispose() {
+    _modifiedCells.clear();
+    _insertedRows.clear();
+    _deletedRowIndices.clear();
+    super.dispose();
+  }
 }
 

lib/features/workspace/result_grid_view.dart

@@ -470,6 +470,9 @@ class _VirtualResultGridState extends material.State<VirtualResultGrid> {
     _horizontalController.dispose();
     _verticalController.dispose();
     _focusNode.dispose();
+    _sortedRows = const [];
+    _columnWidths = const [];
+    _columnOffsets = const [0];
     super.dispose();
   }
 

lib/features/workspace/results_tab.dart

@@ -101,6 +101,14 @@ class _ResultsTabState extends material.State<ResultsTab> {
     return filteredRows;
   }
 
+  @override
+  void dispose() {
+    _memoColumns = null;
+    _memoEffectiveRows = null;
+    _cachedFilteredRows = const [];
+    super.dispose();
+  }
+
   @override
   Widget build(BuildContext context) {
     return QueryaFadeSlide(

test/features/workspace/data_grid_staging_buffer_test.dart

@@ -154,5 +154,22 @@ void main() {
       expect(plan.statements[2].type, MutationType.delete);
       expect(plan.statements[2].sql, 'DELETE FROM "public"."users" WHERE "id" = 3');
     });
+
+    test('dispose clears internal collections and prevents further listener notifications', () {
+      buffer.setCell(0, 1, 'Alice Modified');
+      buffer.addRow(['4', 'Diana', 'diana@test.com']);
+      buffer.toggleDeleteRow(2);
+
+      expect(buffer.isDirty, isTrue);
+      expect(buffer.changeCount, 3);
+
+      buffer.dispose();
+
+      expect(buffer.isDirty, isFalse);
+      expect(buffer.changeCount, 0);
+      expect(buffer.modifiedCellCount, 0);
+      expect(buffer.insertedRowCount, 0);
+      expect(buffer.deletedRowCount, 0);
+    });
   });
 }