hierarchy manipulation

apps/weblibre/lib/features/geckoview/features/browser/presentation/utils/tab_view_reorder.dart

@@ -20,6 +20,7 @@
 import 'package:weblibre/core/logger.dart';
 import 'package:weblibre/features/geckoview/features/browser/presentation/widgets/tab_view/tab_view_item.dart';
 import 'package:weblibre/features/geckoview/features/tabs/data/database/definitions.drift.dart';
+import 'package:weblibre/features/geckoview/features/tabs/domain/entities/tab_parent_change.dart';
 import 'package:weblibre/features/user/data/models/general_settings.dart';
 
 class TabViewReorderResult {
@@ -27,10 +28,16 @@ class TabViewReorderResult {
   final String? previousTabId;
   final String? nextTabId;
 
+  /// Parent assignment implied by the drop position. `unchanged` for plain
+  /// reorders; `detach` / `toParent` only emitted in hierarchical mode when
+  /// the drop lands outside the moving root's current parent scope.
+  final TabParentChange parentChange;
+
   const TabViewReorderResult({
     required this.movingTabIds,
     required this.previousTabId,
     required this.nextTabId,
+    this.parentChange = const TabParentChange.unchanged(),
   });
 }
 
@@ -108,21 +115,31 @@ TabViewReorderResult? buildTabViewReorderResult({
     return null;
   }
 
-  final parentScope = _parentScope(movingItem);
+  // Derive the new parent scope purely from the visual drop position. The
-  final resolvedInsertIndex = _resolveInsertIndexInParentScope(
+  // rule is "adopt the parent of the item you dropped above"; when dropped
+  // past the last visible item, adopt the parent of that last item. This
+  // unifies plain reorder ("same parent as the target slot") and
+  // drag-to-reparent ("different parent than the moving root") behind a
+  // single predicate.
+  final String? newParentScope = _dropParentScopeFor(
     remaining,
     requestedInsertIndex,
-    parentScope,
-    parentById,
   );
-  if (resolvedInsertIndex == null) {
+
-    logger.t(
+  // Cycle guard: the new parent must not be inside the moving subtree.
-      'reorder snapped: no anchor for parent scope $parentScope — drop '
+  if (newParentScope != null && moveBlockIds.contains(newParentScope)) {
-      'rejected so the moving tab stays in its original parent',
+    logger.t('reorder refused: new parent scope is inside moving subtree');
-    );
     return null;
   }
 
+  final originalParentScope = _parentScope(movingItem);
+  final TabParentChange parentChange = newParentScope == originalParentScope
+      ? const TabParentChange.unchanged()
+      : newParentScope == null
+      ? const TabParentChange.detach()
+      : TabParentChange.toParent(newParentScope);
+  final resolvedInsertIndex = requestedInsertIndex.clamp(0, remaining.length);
+
   final reorderedBlocks = remaining.toList()
     ..insert(resolvedInsertIndex, movingItem);
 
@@ -204,9 +221,26 @@ TabViewReorderResult? buildTabViewReorderResult({
       movingPartitionRootId: _rootIdFor(movingItem.tabId, parentById),
       sortPinnedFirst: sortPinnedFirst,
     ),
+    parentChange: parentChange,
   );
 }
 
+/// Returns the parent scope implied by dropping just before
+/// `remaining[insertIndex]` (or "at the end" when `insertIndex == length`).
+///
+/// Rule: adopt the parent of the item you dropped above. For a tail-drop,
+/// adopt the parent of the last item. The resulting scope is the
+/// candidate `parent_id` for the moving subtree's root.
+String? _dropParentScopeFor(List<TabViewItem> remaining, int insertIndex) {
+  if (remaining.isEmpty) {
+    return null;
+  }
+  if (insertIndex < remaining.length) {
+    return _parentScope(remaining[insertIndex]);
+  }
+  return _parentScope(remaining.last);
+}
+
 List<String> _orderedIdsForStorageAnchors(
   List<String> orderedTabIds, {
   required TabDirection tabListDirection,
@@ -237,6 +271,7 @@ List<String> _orderedIdsForStorageAnchors(
 TabViewReorderResult? _resultFromOrderedIds({
   required List<String> movingTabIds,
   required List<String> orderedTabIds,
+  TabParentChange parentChange = const TabParentChange.unchanged(),
 }) {
   if (movingTabIds.isEmpty) {
     return null;
@@ -260,114 +295,12 @@ TabViewReorderResult? _resultFromOrderedIds({
     nextTabId: lastIndex + 1 < orderedTabIds.length
         ? orderedTabIds[lastIndex + 1]
         : null,
+    parentChange: parentChange,
   );
 }
 
 String? _parentScope(TabViewItem item) => item.childItem?.parentId;
 
-int? _resolveInsertIndexInParentScope(
-  List<TabViewItem> items,
-  int requestedInsertIndex,
-  String? parentScope,
-  Map<String, String?> parentById,
-) {
-  final target = requestedInsertIndex < items.length
-      ? items[requestedInsertIndex]
-      : null;
-
-  if (target != null && _isDirectScopeAnchor(target, parentScope, parentById)) {
-    return target.tabId == parentScope
-        ? requestedInsertIndex + 1
-        : requestedInsertIndex;
-  }
-
-  final previousAnchorIndex = _nearestPreviousScopeAnchorIndex(
-    items,
-    requestedInsertIndex - 1,
-    parentScope,
-    parentById,
-  );
-  if (previousAnchorIndex != null) {
-    return _indexAfterVisibleSubtree(items, previousAnchorIndex, parentById);
-  }
-
-  return _nearestNextScopeAnchorIndex(
-    items,
-    requestedInsertIndex,
-    parentScope,
-    parentById,
-  );
-}
-
-bool _isDirectScopeAnchor(
-  TabViewItem item,
-  String? parentScope,
-  Map<String, String?> parentById,
-) {
-  return item.tabId == parentScope || parentById[item.tabId] == parentScope;
-}
-
-int? _nearestPreviousScopeAnchorIndex(
-  List<TabViewItem> items,
-  int startIndex,
-  String? parentScope,
-  Map<String, String?> parentById,
-) {
-  for (var i = startIndex; i >= 0; i--) {
-    if (_isDirectScopeAnchor(items[i], parentScope, parentById)) {
-      return i;
-    }
-  }
-  return null;
-}
-
-int? _nearestNextScopeAnchorIndex(
-  List<TabViewItem> items,
-  int startIndex,
-  String? parentScope,
-  Map<String, String?> parentById,
-) {
-  for (var i = startIndex; i < items.length; i++) {
-    if (_isDirectScopeAnchor(items[i], parentScope, parentById)) {
-      return items[i].tabId == parentScope ? i + 1 : i;
-    }
-  }
-  return null;
-}
-
-int _indexAfterVisibleSubtree(
-  List<TabViewItem> items,
-  int anchorIndex,
-  Map<String, String?> parentById,
-) {
-  final anchorId = items[anchorIndex].tabId;
-  var index = anchorIndex + 1;
-  while (index < items.length &&
-      _isDescendantOf(items[index].tabId, anchorId, parentById)) {
-    index++;
-  }
-  return index;
-}
-
-bool _isDescendantOf(
-  String tabId,
-  String ancestorId,
-  Map<String, String?> parentById,
-) {
-  var parentId = parentById[tabId];
-  final seen = <String>{tabId};
-  while (parentId != null) {
-    if (parentId == ancestorId) {
-      return true;
-    }
-    if (!seen.add(parentId)) {
-      return false;
-    }
-    parentId = parentById[parentId];
-  }
-  return false;
-}
-
 Map<String, List<TabsWithRootAndDepthResult>> _buildChildrenByParent(
   Map<String, TabsWithRootAndDepthResult> rowsById,
   Map<String, String?> parentById,

apps/weblibre/lib/features/geckoview/features/browser/presentation/widgets/tab_menu.dart

@@ -38,6 +38,7 @@ import 'package:weblibre/features/geckoview/domain/providers/tab_state.dart';
 import 'package:weblibre/features/geckoview/domain/repositories/tab.dart';
 import 'package:weblibre/features/geckoview/features/browser/presentation/widgets/menu_item_buttons.dart';
 import 'package:weblibre/features/geckoview/features/browser/presentation/widgets/navigation_buttons.dart';
+import 'package:weblibre/features/geckoview/features/browser/presentation/widgets/tab_view/dialogs/tab_parent_picker.dart';
 import 'package:weblibre/features/geckoview/features/browser/presentation/widgets/translation_bottom_sheet.dart';
 import 'package:weblibre/features/geckoview/features/find_in_page/presentation/controllers/find_in_page.dart';
 import 'package:weblibre/features/geckoview/features/pwa/domain/providers.dart';
@@ -50,6 +51,7 @@ import 'package:weblibre/features/geckoview/features/tabs/domain/entities/contai
 import 'package:weblibre/features/geckoview/features/tabs/domain/providers.dart';
 import 'package:weblibre/features/geckoview/features/tabs/domain/repositories/container.dart';
 import 'package:weblibre/features/geckoview/features/tabs/domain/repositories/tab.dart';
+import 'package:weblibre/features/user/data/models/general_settings.dart';
 import 'package:weblibre/features/user/domain/repositories/general_settings.dart';
 import 'package:weblibre/features/web_search/domain/controllers/sandbox_capture_controller.dart';
 import 'package:weblibre/presentation/hooks/menu_controller.dart';
@@ -74,6 +76,7 @@ class TabMenu extends HookConsumerWidget {
   final bool enablePinTab;
   final bool enableReloadButton;
   final bool enableNavigationButtons;
+  final bool enableHierarchy;
 
   const TabMenu({
     super.key,
@@ -94,6 +97,7 @@ class TabMenu extends HookConsumerWidget {
     this.enablePinTab = true,
     this.enableReloadButton = true,
     this.enableNavigationButtons = true,
+    this.enableHierarchy = true,
   });
 
   @override
@@ -560,6 +564,84 @@ class TabMenu extends HookConsumerWidget {
             leadingIcon: const Icon(MdiIcons.folder),
             child: const Text('Container'),
           ),
+        if (enableHierarchy)
+          Consumer(
+            builder: (childContext, childRef, child) {
+              // `MenuItemButton.onPressed` is dispatched as a post-frame
+              // callback by Flutter's menu_anchor — by the time it fires,
+              // this `Consumer` element (and any context/ref captured from
+              // its builder params) has been deactivated as the menu
+              // overlay tears down. So:
+              //  - use `childContext` / `childRef` only synchronously
+              //    inside this builder (the `watch` below),
+              //  - inside `onPressed`, use the outer `context` and `ref`
+              //    from TabMenu.build, which live above the menu overlay
+              //    and stay mounted with the trigger button.
+              final movingTab = childRef.watch(
+                watchTabDbDataProvider(selectedTabId),
+              );
+              final tabData = movingTab.value;
+              final hasParent = tabData?.parentId != null;
+
+              final repo = ref.read(tabDataRepositoryProvider.notifier);
+
+              return SubmenuButton(
+                leadingIcon: const Icon(MdiIcons.fileTree),
+                menuChildren: [
+                  MenuItemButton(
+                    leadingIcon: const Icon(MdiIcons.swapHorizontal),
+                    onPressed: () async {
+                      controller.close();
+                      await showTabParentPicker(
+                        context: context,
+                        ref: ref,
+                        tabId: selectedTabId,
+                      );
+                    },
+                    child: const Text('Change parent…'),
+                  ),
+                  MenuItemButton(
+                    leadingIcon: const Icon(MdiIcons.fileTreeOutline),
+                    onPressed: hasParent
+                        ? () async {
+                            await repo.setTabParent(
+                              tabId: selectedTabId,
+                              newParentId: null,
+                            );
+                          }
+                        : null,
+                    child: const Text('Detach from parent'),
+                  ),
+                  const Divider(),
+                  MenuItemButton(
+                    leadingIcon: const Icon(MdiIcons.chevronUp),
+                    onPressed: () async {
+                      await repo.moveTabAmongSiblings(
+                        selectedTabId,
+                        down:
+                            settings.tabListDirection ==
+                            TabDirection.newestFirst,
+                      );
+                    },
+                    child: const Text('Move up'),
+                  ),
+                  MenuItemButton(
+                    leadingIcon: const Icon(MdiIcons.chevronDown),
+                    onPressed: () async {
+                      await repo.moveTabAmongSiblings(
+                        selectedTabId,
+                        down:
+                            settings.tabListDirection !=
+                            TabDirection.newestFirst,
+                      );
+                    },
+                    child: const Text('Move down'),
+                  ),
+                ],
+                child: const Text('Hierarchy'),
+              );
+            },
+          ),
         if (enableShare)
           SubmenuButton(
             menuChildren: [

apps/weblibre/lib/features/geckoview/features/browser/presentation/widgets/tab_view/dialogs/tab_parent_picker.dart

@@ -0,0 +1,198 @@
+/*
+ * Copyright (c) 2024-2026 Fabian Freund.
+ *
+ * This file is part of WebLibre
+ * (see https://weblibre.eu).
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+import 'package:flutter/material.dart';
+import 'package:flutter_material_design_icons/flutter_material_design_icons.dart';
+import 'package:hooks_riverpod/hooks_riverpod.dart';
+import 'package:weblibre/features/geckoview/features/browser/presentation/widgets/tab_view/tab_preview.dart';
+import 'package:weblibre/features/geckoview/features/tabs/domain/providers.dart';
+import 'package:weblibre/features/geckoview/features/tabs/domain/repositories/tab.dart';
+
+/// Matches the fixed itemExtent used by the main tab list
+/// (`tab_list_view.dart`'s `_itemHeight`).
+const double _itemExtent = 86.0;
+
+/// Outcome of the parent picker sheet. Mirrors the
+/// `ContainerSelectionResult` shape so the sheet can pop a discriminated
+/// value rather than relying on sentinels or string conventions.
+sealed class _ParentPickerSelection {
+  const _ParentPickerSelection();
+}
+
+class _ParentPickerDetach extends _ParentPickerSelection {
+  const _ParentPickerDetach();
+}
+
+class _ParentPickerSelected extends _ParentPickerSelection {
+  final String parentTabId;
+  const _ParentPickerSelected(this.parentTabId);
+}
+
+/// Modal bottom sheet that lets the user pick a new parent for [tabId],
+/// or detach it from its current parent.
+///
+/// Candidates are all tabs in the moving tab's container, minus the moving
+/// tab itself and its descendants (cycle guard). Tapping the persistent
+/// "Make standalone" entry detaches the tab.
+Future<void> showTabParentPicker({
+  required BuildContext context,
+  required WidgetRef ref,
+  required String tabId,
+}) async {
+  // Capture the notifier synchronously: by the time the modal pops,
+  // the calling widget (and its `ref`) may have unmounted, but the
+  // Riverpod notifier itself is keepAlive and safe to use post-await.
+  final repo = ref.read(tabDataRepositoryProvider.notifier);
+
+  final selection = await showModalBottomSheet<_ParentPickerSelection>(
+    context: context,
+    isScrollControlled: true,
+    showDragHandle: true,
+    builder: (context) => _TabParentPickerSheet(tabId: tabId),
+  );
+
+  switch (selection) {
+    case null:
+      return;
+    case _ParentPickerDetach():
+      await repo.setTabParent(tabId: tabId, newParentId: null);
+    case _ParentPickerSelected(:final parentTabId):
+      await repo.setTabParent(tabId: tabId, newParentId: parentTabId);
+  }
+}
+
+class _TabParentPickerSheet extends HookConsumerWidget {
+  final String tabId;
+
+  const _TabParentPickerSheet({required this.tabId});
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    final movingTabAsync = ref.watch(watchTabDbDataProvider(tabId));
+    final descendantsAsync = ref.watch(watchTabDescendantsProvider(tabId));
+
+    return DraggableScrollableSheet(
+      expand: false,
+      initialChildSize: 0.6,
+      minChildSize: 0.3,
+      maxChildSize: 0.95,
+      builder: (context, scrollController) {
+        return movingTabAsync.when(
+          loading: () => const Center(child: CircularProgressIndicator()),
+          error: (e, _) => Center(child: Text('Error: $e')),
+          data: (movingTab) {
+            if (movingTab == null) {
+              return const Center(child: Text('Tab no longer exists'));
+            }
+            return descendantsAsync.when(
+              loading: () => const Center(child: CircularProgressIndicator()),
+              error: (e, _) => Center(child: Text('Error: $e')),
+              data: (descendants) {
+                final excluded = descendants.keys.toSet()..add(tabId);
+                final containerId = movingTab.containerId;
+                final candidatesAsync = ref.watch(
+                  watchContainerTabsDataProvider(containerId),
+                );
+                return candidatesAsync.when(
+                  loading: () =>
+                      const Center(child: CircularProgressIndicator()),
+                  error: (e, _) => Center(child: Text('Error: $e')),
+                  data: (tabs) {
+                    final candidates = tabs
+                        .where((t) => !excluded.contains(t.id))
+                        .toList();
+                    return CustomScrollView(
+                      controller: scrollController,
+                      slivers: [
+                        const SliverPadding(
+                          padding: EdgeInsets.fromLTRB(16, 8, 16, 8),
+                          sliver: SliverToBoxAdapter(
+                            child: Text(
+                              'Choose a parent tab',
+                              style: TextStyle(
+                                fontSize: 18,
+                                fontWeight: FontWeight.w600,
+                              ),
+                            ),
+                          ),
+                        ),
+                        SliverToBoxAdapter(
+                          child: ListTile(
+                            leading: const Icon(MdiIcons.fileTreeOutline),
+                            title: const Text('Make standalone'),
+                            subtitle: const Text(
+                              'Detach from current parent',
+                            ),
+                            enabled: movingTab.parentId != null,
+                            onTap: () => Navigator.of(
+                              context,
+                            ).pop(const _ParentPickerDetach()),
+                          ),
+                        ),
+                        const SliverToBoxAdapter(child: Divider(height: 1)),
+                        if (candidates.isEmpty)
+                          const SliverToBoxAdapter(
+                            child: Padding(
+                              padding: EdgeInsets.all(24),
+                              child: Text(
+                                'No candidate tabs in this container.',
+                                textAlign: TextAlign.center,
+                              ),
+                            ),
+                          )
+                        else
+                          // Match the tab list view's fixed itemExtent.
+                          // `ListTabPreview` has no intrinsic height — its
+                          // thumbnail variant uses `BoxFit.fitHeight`, which
+                          // needs a bounded parent or it sizes to the
+                          // image's native dimensions and overflows.
+                          SliverFixedExtentList.builder(
+                            itemExtent: _itemExtent,
+                            itemCount: candidates.length,
+                            itemBuilder: (context, index) {
+                              final candidate = candidates[index];
+                              // `isActive` highlights the current parent
+                              // with the same accent the tab list uses for
+                              // the selected tab — semantically "this is
+                              // the one you're currently nested under".
+                              return ListTabPreview(
+                                tabId: candidate.id,
+                                isActive:
+                                    candidate.id == movingTab.parentId,
+                                onTap: () => Navigator.of(
+                                  context,
+                                ).pop(_ParentPickerSelected(candidate.id)),
+                              );
+                            },
+                          ),
+                        const SliverPadding(
+                          padding: EdgeInsets.only(bottom: 16),
+                        ),
+                      ],
+                    );
+                  },
+                );
+              },
+            );
+          },
+        );
+      },
+    );
+  }
+}

apps/weblibre/lib/features/geckoview/features/browser/presentation/widgets/tab_view/tab_grid_view.dart

@@ -399,6 +399,7 @@ class _TabGridView extends HookConsumerWidget {
                           movingTabIds: result.movingTabIds,
                           previousTabId: result.previousTabId,
                           nextTabId: result.nextTabId,
+                          parentChange: result.parentChange,
                         );
                   },
                   childBuilder: (reorderableItemBuilder) {

apps/weblibre/lib/features/geckoview/features/browser/presentation/widgets/tab_view/tab_list_view.dart

@@ -458,6 +458,7 @@ class _TabListView extends HookConsumerWidget {
                           movingTabIds: result.movingTabIds,
                           previousTabId: result.previousTabId,
                           nextTabId: result.nextTabId,
+                          parentChange: result.parentChange,
                         );
                   },
                   itemBuilder: (context, index) {

apps/weblibre/lib/features/geckoview/features/tabs/data/database/daos/tab.dart

@@ -31,6 +31,7 @@ import 'package:weblibre/features/geckoview/features/tabs/data/entities/tab_mode
 import 'package:weblibre/features/geckoview/features/tabs/data/entities/tab_source.dart';
 import 'package:weblibre/features/geckoview/features/tabs/data/models/container_data.dart';
 import 'package:weblibre/features/geckoview/features/tabs/data/models/tab_query_result.dart';
+import 'package:weblibre/features/geckoview/features/tabs/domain/entities/tab_parent_change.dart';
 
 class SyncTabsResult {
   final Set<String> deletedIsolationContextIds;
@@ -188,7 +189,14 @@ class TabDao extends DatabaseAccessor<TabDatabase> with $TabDaoMixin {
           .getLastChildTabId(containerId.value, parentId.value!)
           .getSingleOrNull();
 
-      final anchorTabId = lastChildId ?? parentId.value!;
+      final lastChildSubtreeId = lastChildId == null
+          ? null
+          : await lastSubtreeTabIdByOrderKey(
+              lastChildId,
+              containerId: containerId.value,
+            ).getSingleOrNull();
+
+      final anchorTabId = lastChildSubtreeId ?? lastChildId ?? parentId.value!;
 
       final key = await db.containerDao
           .generateOrderKeyAfterTabId(containerId.value, anchorTabId)
@@ -433,6 +441,7 @@ class TabDao extends DatabaseAccessor<TabDatabase> with $TabDaoMixin {
     required List<String> movingTabIds,
     required String? previousTabId,
     required String? nextTabId,
+    TabParentChange parentChange = const TabParentChange.unchanged(),
   }) {
     if (movingTabIds.isEmpty) {
       return Future.value();
@@ -468,11 +477,46 @@ class TabDao extends DatabaseAccessor<TabDatabase> with $TabDaoMixin {
         nextRank: nextRank,
       );
 
+      // Resolve the parent_id / container_id companion values once.
+      //
+      // For a `TabParentToSpecific` whose target row is missing, fall back
+      // to "unchanged" so we don't issue a parent_id FK violation — the
+      // caller passed a stale id, but the order_key change is still
+      // useful. The container cascade fires whenever the parent_id is
+      // being assigned to a concrete tab (including unassigned parents,
+      // container_id = null), since `tabsWithRootAndDepth` is
+      // container-scoped and a divergent child would vanish from
+      // hierarchical views.
+      Value<String?> parentValue = const Value.absent();
+      Value<String?> containerValue = const Value.absent();
+      switch (parentChange) {
+        case TabParentUnchanged():
+          break;
+        case TabParentDetach():
+          parentValue = const Value(null);
+        case TabParentToSpecific(:final parentTabId):
+          final parent =
+              anchors[parentTabId] ??
+              await getTabDataById(parentTabId).getSingleOrNull();
+          if (parent != null) {
+            parentValue = Value(parentTabId);
+            containerValue = Value(parent.containerId);
+          }
+      }
+
       await batch((batch) {
         for (var i = 0; i < movingTabIds.length; i++) {
+          final isRoot = i == 0;
           batch.update(
             db.tab,
-            TabCompanion(orderKey: Value(orderKeys[i])),
+            TabCompanion(
+              orderKey: Value(orderKeys[i]),
+              // parent_id change applies only to the moving root;
+              // descendants keep their existing parent_id pointers.
+              parentId: isRoot ? parentValue : const Value.absent(),
+              // Container cascade applies to the whole subtree.
+              containerId: containerValue,
+            ),
             where: (t) => t.id.equals(movingTabIds[i]),
           );
         }
@@ -480,6 +524,303 @@ class TabDao extends DatabaseAccessor<TabDatabase> with $TabDaoMixin {
     });
   }
 
+  /// Returns the recursive set of [tabId] and its descendants.
+  Future<Set<String>> _collectSubtreeIds(String tabId) async {
+    final rows = await db.definitionsDrift
+        .unorderedTabDescendants(tabId: tabId)
+        .get();
+    return {for (final r in rows) r.id};
+  }
+
+  /// Re-parents [tabId] to [newParentId] (or detaches when null).
+  ///
+  /// Returns `true` on success, `false` when the move was rejected
+  /// (cycle, unknown tab, or no-op).
+  ///
+  /// - Cycle-safe: rejects when [newParentId] is the moving tab itself or
+  ///   any of its descendants.
+  /// - When attaching to a non-null parent, the whole moving subtree adopts
+  ///   the new parent's `container_id` (otherwise the row vanishes from
+  ///   hierarchical views, which are container-scoped).
+  /// - Slots the moving subtree immediately after the new parent's last
+  ///   existing child (or after the parent itself if it has none), as an
+  ///   atomic order_key block. When detaching, order_keys are left
+  ///   untouched — the tab simply becomes a root in its current slot.
+  Future<bool> setTabParent({
+    required String tabId,
+    required String? newParentId,
+  }) {
+    if (tabId == newParentId) {
+      return Future.value(false);
+    }
+
+    return db.transaction(() async {
+      final movingTab = await getTabDataById(tabId).getSingleOrNull();
+      if (movingTab == null) {
+        return false;
+      }
+      if (movingTab.parentId == newParentId) {
+        return false;
+      }
+
+      final subtreeIds = await _collectSubtreeIds(tabId);
+
+      String? targetContainerId;
+      if (newParentId != null) {
+        if (subtreeIds.contains(newParentId)) {
+          return false;
+        }
+        final newParent = await getTabDataById(newParentId).getSingleOrNull();
+        if (newParent == null) {
+          return false;
+        }
+        targetContainerId = newParent.containerId;
+      } else {
+        targetContainerId = movingTab.containerId;
+      }
+
+      // Cascade container update for the whole subtree when crossing
+      // container boundaries. `tabsWithRootAndDepth` is container-scoped
+      // — a child whose `container_id` differs from its parent's would
+      // vanish from hierarchical views.
+      if (targetContainerId != movingTab.containerId) {
+        await (update(db.tab)..where((t) => t.id.isIn(subtreeIds))).write(
+          TabCompanion(containerId: Value(targetContainerId)),
+        );
+      }
+
+      if (newParentId == null) {
+        // Detach: keep existing order_keys. The row becomes a root in its
+        // current slot and the subtree under it stays intact.
+        await _updateByIdStatement(
+          tabId,
+        ).write(const TabCompanion(parentId: Value(null)));
+        return true;
+      }
+
+      // Pull the (now container-adjusted) subtree rows so we can re-rank
+      // them as an atomic block. We must compute anchors BEFORE writing
+      // the new parent_id, otherwise `getLastChildTabId(newParentId)`
+      // would pick up the moving root itself as a sibling.
+      final subtreeRows =
+          await (select(db.tab)
+                ..where((t) => t.id.isIn(subtreeIds))
+                ..orderBy([(t) => OrderingTerm.asc(t.orderKey)]))
+              .get();
+      final orderedIds = subtreeRows.map((r) => r.id).toList();
+      if (orderedIds.isEmpty) {
+        return true;
+      }
+
+      final lastSiblingId = await db.containerDao
+          .getLastChildTabId(targetContainerId, newParentId)
+          .getSingleOrNull();
+      final lastSiblingSubtreeId = lastSiblingId == null
+          ? null
+          : await lastSubtreeTabIdByOrderKey(
+              lastSiblingId,
+              containerId: targetContainerId,
+            ).getSingleOrNull();
+      final anchorId = lastSiblingSubtreeId ?? lastSiblingId ?? newParentId;
+
+      final anchorRow = await getTabDataById(anchorId).getSingleOrNull();
+      if (anchorRow == null) {
+        return false;
+      }
+      final previousRank = LexoRank.parse(anchorRow.orderKey);
+
+      // Next-rank = first non-subtree tab in the destination container with
+      // order_key strictly greater than the anchor. Skipping subtree members
+      // keeps the moved block compact even when the subtree's old keys
+      // sat near the anchor in storage.
+      final nextRow =
+          await (select(db.tab)
+                ..where((t) {
+                  final containerEq = targetContainerId != null
+                      ? t.containerId.equals(targetContainerId)
+                      : t.containerId.isNull();
+                  return containerEq &
+                      t.orderKey.isBiggerThanValue(anchorRow.orderKey) &
+                      t.id.isNotIn(subtreeIds);
+                })
+                ..orderBy([(t) => OrderingTerm.asc(t.orderKey)])
+                ..limit(1))
+              .getSingleOrNull();
+      final nextRank = nextRow == null
+          ? null
+          : LexoRank.parse(nextRow.orderKey);
+
+      final orderKeys = _generateOrderKeysBetween(
+        count: orderedIds.length,
+        previousRank: previousRank,
+        nextRank: nextRank,
+      );
+
+      await batch((batch) {
+        // parent_id change is applied on the moving root only; subtree
+        // descendants keep their existing parent_id pointers.
+        batch.update(
+          db.tab,
+          TabCompanion(
+            parentId: Value(newParentId),
+            orderKey: Value(orderKeys[0]),
+          ),
+          where: (t) => t.id.equals(orderedIds[0]),
+        );
+        for (var i = 1; i < orderedIds.length; i++) {
+          batch.update(
+            db.tab,
+            TabCompanion(orderKey: Value(orderKeys[i])),
+            where: (t) => t.id.equals(orderedIds[i]),
+          );
+        }
+      });
+
+      return true;
+    });
+  }
+
+  /// Swaps a direct child with its parent: the child takes the parent's
+  /// slot in the tree (parent_id + order_key), and the parent becomes a
+  /// child of the (formerly) child, placed after its existing siblings.
+  ///
+  /// Returns `false` when [childId] has no parent or the tabs cross a
+  /// container boundary (which would imply data corruption).
+  Future<bool> promoteChildToParent(String childId) {
+    return db.transaction(() async {
+      final child = await getTabDataById(childId).getSingleOrNull();
+      if (child == null || child.parentId == null) {
+        return false;
+      }
+      final parentId = child.parentId!;
+      final parent = await getTabDataById(parentId).getSingleOrNull();
+      if (parent == null) {
+        return false;
+      }
+      if (parent.containerId != child.containerId) {
+        return false;
+      }
+
+      final containerId = child.containerId;
+
+      // The (about-to-be-demoted) parent gets placed after the new
+      // parent's (= former child's) existing other children. We read the
+      // anchor's order_key BEFORE any writes — `generateOrderKeyAfterTabId`
+      // reads from storage, so the captured key reflects pre-swap state.
+      final lastChildOfChild = await db.containerDao
+          .getLastChildTabId(containerId, childId)
+          .getSingleOrNull();
+      final lastChildSubtreeId = lastChildOfChild == null
+          ? null
+          : await lastSubtreeTabIdByOrderKey(
+              lastChildOfChild,
+              containerId: containerId,
+            ).getSingleOrNull();
+      final anchorId = lastChildSubtreeId ?? lastChildOfChild ?? childId;
+      final newParentOrderKey = await db.containerDao
+          .generateOrderKeyAfterTabId(containerId, anchorId)
+          .getSingleOrNull();
+      if (newParentOrderKey == null) {
+        return false;
+      }
+
+      await batch((batch) {
+        batch.update(
+          db.tab,
+          TabCompanion(
+            parentId: Value(parent.parentId),
+            orderKey: Value(parent.orderKey),
+          ),
+          where: (t) => t.id.equals(childId),
+        );
+        batch.update(
+          db.tab,
+          TabCompanion(
+            parentId: Value(childId),
+            orderKey: Value(newParentOrderKey),
+          ),
+          where: (t) => t.id.equals(parentId),
+        );
+      });
+
+      return true;
+    });
+  }
+
+  /// Moves [tabId] one sibling slot up (or down) within its parent scope,
+  /// carrying its whole subtree as an atomic block.
+  ///
+  /// Returns `false` when the tab is unknown or already at the relevant
+  /// end of its sibling list.
+  Future<bool> moveTabAmongSiblings(String tabId, {required bool down}) {
+    // Transactional so the sibling-list read, subtree resolution, and the
+    // anchor lookup all observe the same DB snapshot. `reorderTabs` opens
+    // a nested savepoint internally, which is fine.
+    return db.transaction(() async {
+      final tab = await getTabDataById(tabId).getSingleOrNull();
+      if (tab == null) {
+        return false;
+      }
+
+      final siblings =
+          await (select(db.tab)
+                ..where((t) {
+                  final containerEq = tab.containerId != null
+                      ? t.containerId.equals(tab.containerId!)
+                      : t.containerId.isNull();
+                  final parentEq = tab.parentId != null
+                      ? t.parentId.equals(tab.parentId!)
+                      : t.parentId.isNull();
+                  return containerEq & parentEq;
+                })
+                ..orderBy([(t) => OrderingTerm.asc(t.orderKey)]))
+              .get();
+
+      final idx = siblings.indexWhere((s) => s.id == tabId);
+      if (idx < 0) {
+        return false;
+      }
+      final newIdx = down ? idx + 1 : idx - 1;
+      if (newIdx < 0 || newIdx >= siblings.length) {
+        return false;
+      }
+
+      final reordered = siblings.toList()..removeAt(idx);
+      reordered.insert(newIdx, tab);
+
+      final previousIdx = newIdx - 1;
+      final nextIdx = newIdx + 1;
+      final previousSiblingId = previousIdx >= 0
+          ? reordered[previousIdx].id
+          : null;
+      final previousTabId = previousSiblingId == null
+          ? null
+          : await lastSubtreeTabIdByOrderKey(
+                  previousSiblingId,
+                  containerId: tab.containerId,
+                ).getSingleOrNull() ??
+                previousSiblingId;
+      final nextTabId = nextIdx < reordered.length
+          ? reordered[nextIdx].id
+          : null;
+
+      final subtreeIds = await _collectSubtreeIds(tabId);
+      final subtreeRows =
+          await (select(db.tab)
+                ..where((t) => t.id.isIn(subtreeIds))
+                ..orderBy([(t) => OrderingTerm.asc(t.orderKey)]))
+              .get();
+      final movingTabIds = subtreeRows.map((r) => r.id).toList();
+
+      await reorderTabs(
+        movingTabIds: movingTabIds,
+        previousTabId: previousTabId,
+        nextTabId: nextTabId,
+      );
+      return true;
+    });
+  }
+
   List<String> _generateOrderKeysBetween({
     required int count,
     required LexoRank? previousRank,

apps/weblibre/lib/features/geckoview/features/tabs/domain/entities/tab_parent_change.dart

@@ -0,0 +1,49 @@
+/*
+ * Copyright (c) 2024-2026 Fabian Freund.
+ *
+ * This file is part of WebLibre
+ * (see https://weblibre.eu).
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/// How a reorder/reparent operation should affect the moving tab's
+/// `parent_id`. Distinguishes "leave parent_id alone" (the default for a
+/// plain reorder) from "detach to root" and "attach to a specific tab".
+///
+/// Mirrors the shape of [TabContainerSelection].
+sealed class TabParentChange {
+  const TabParentChange();
+
+  const factory TabParentChange.unchanged() = TabParentUnchanged;
+
+  const factory TabParentChange.detach() = TabParentDetach;
+
+  const factory TabParentChange.toParent(String parentTabId) =
+      TabParentToSpecific;
+}
+
+final class TabParentUnchanged extends TabParentChange {
+  const TabParentUnchanged();
+}
+
+final class TabParentDetach extends TabParentChange {
+  const TabParentDetach();
+}
+
+final class TabParentToSpecific extends TabParentChange {
+  final String parentTabId;
+
+  const TabParentToSpecific(this.parentTabId);
+}

apps/weblibre/lib/features/geckoview/features/tabs/domain/providers.dart

@@ -108,6 +108,12 @@ Stream<List<TabsWithRootAndDepthResult>> watchTabsWithRootAndDepth(
       .watch();
 }
 
+@Riverpod()
+Stream<TabData?> watchTabDbData(Ref ref, String tabId) {
+  final db = ref.watch(tabDatabaseProvider);
+  return db.tabDao.getTabDataById(tabId).watchSingleOrNull();
+}
+
 @Riverpod()
 Stream<Map<String, String?>> watchTabDescendants(Ref ref, String tabId) {
   final db = ref.watch(tabDatabaseProvider);

apps/weblibre/lib/features/geckoview/features/tabs/domain/providers.g.dart

@@ -453,6 +453,76 @@ final class WatchTabsWithRootAndDepthFamily extends $Family
   String toString() => r'watchTabsWithRootAndDepthProvider';
 }
 
+@ProviderFor(watchTabDbData)
+final watchTabDbDataProvider = WatchTabDbDataFamily._();
+
+final class WatchTabDbDataProvider
+    extends
+        $FunctionalProvider<AsyncValue<TabData?>, TabData?, Stream<TabData?>>
+    with $FutureModifier<TabData?>, $StreamProvider<TabData?> {
+  WatchTabDbDataProvider._({
+    required WatchTabDbDataFamily super.from,
+    required String super.argument,
+  }) : super(
+         retry: null,
+         name: r'watchTabDbDataProvider',
+         isAutoDispose: true,
+         dependencies: null,
+         $allTransitiveDependencies: null,
+       );
+
+  @override
+  String debugGetCreateSourceHash() => _$watchTabDbDataHash();
+
+  @override
+  String toString() {
+    return r'watchTabDbDataProvider'
+        ''
+        '($argument)';
+  }
+
+  @$internal
+  @override
+  $StreamProviderElement<TabData?> $createElement($ProviderPointer pointer) =>
+      $StreamProviderElement(pointer);
+
+  @override
+  Stream<TabData?> create(Ref ref) {
+    final argument = this.argument as String;
+    return watchTabDbData(ref, argument);
+  }
+
+  @override
+  bool operator ==(Object other) {
+    return other is WatchTabDbDataProvider && other.argument == argument;
+  }
+
+  @override
+  int get hashCode {
+    return argument.hashCode;
+  }
+}
+
+String _$watchTabDbDataHash() => r'c505be1cdeaffced2615fdb075ed8a9a2132754a';
+
+final class WatchTabDbDataFamily extends $Family
+    with $FunctionalFamilyOverride<Stream<TabData?>, String> {
+  WatchTabDbDataFamily._()
+    : super(
+        retry: null,
+        name: r'watchTabDbDataProvider',
+        dependencies: null,
+        $allTransitiveDependencies: null,
+        isAutoDispose: true,
+      );
+
+  WatchTabDbDataProvider call(String tabId) =>
+      WatchTabDbDataProvider._(argument: tabId, from: this);
+
+  @override
+  String toString() => r'watchTabDbDataProvider';
+}
+
 @ProviderFor(watchTabDescendants)
 final watchTabDescendantsProvider = WatchTabDescendantsFamily._();
 

apps/weblibre/lib/features/geckoview/features/tabs/domain/repositories/tab.dart

@@ -27,6 +27,7 @@ import 'package:weblibre/features/geckoview/features/tabs/data/database/definiti
 import 'package:weblibre/features/geckoview/features/tabs/data/entities/tab_mode.dart';
 import 'package:weblibre/features/geckoview/features/tabs/data/models/container_data.dart';
 import 'package:weblibre/features/geckoview/features/tabs/data/providers.dart';
+import 'package:weblibre/features/geckoview/features/tabs/domain/entities/tab_parent_change.dart';
 
 part 'tab.g.dart';
 
@@ -126,6 +127,7 @@ class TabDataRepository extends _$TabDataRepository {
     required List<String> movingTabIds,
     required String? previousTabId,
     required String? nextTabId,
+    TabParentChange parentChange = const TabParentChange.unchanged(),
   }) {
     return ref
         .read(tabDatabaseProvider)
@@ -134,9 +136,37 @@ class TabDataRepository extends _$TabDataRepository {
           movingTabIds: movingTabIds,
           previousTabId: previousTabId,
           nextTabId: nextTabId,
+          parentChange: parentChange,
         );
   }
 
+  Future<bool> setTabParent({
+    required String tabId,
+    required String? newParentId,
+  }) {
+    return ref
+        .read(tabDatabaseProvider)
+        .tabDao
+        .setTabParent(tabId: tabId, newParentId: newParentId);
+  }
+
+  Future<bool> promoteChildToParent(String childId) {
+    return ref
+        .read(tabDatabaseProvider)
+        .tabDao
+        .promoteChildToParent(childId);
+  }
+
+  Future<bool> moveTabAmongSiblings(
+    String tabId, {
+    required bool down,
+  }) {
+    return ref
+        .read(tabDatabaseProvider)
+        .tabDao
+        .moveTabAmongSiblings(tabId, down: down);
+  }
+
   Future<int> closeAllTabs({
     bool includeRegular = true,
     bool includePrivate = true,

apps/weblibre/lib/features/geckoview/features/tabs/domain/repositories/tab.g.dart

@@ -41,7 +41,7 @@ final class TabDataRepositoryProvider
   }
 }
 
-String _$tabDataRepositoryHash() => r'e14144f832ce32e1ae349df8970d025036526bc0';
+String _$tabDataRepositoryHash() => r'2208b806a97f239a5b3e6ed7e6c395cbd0276bdd';
 
 abstract class _$TabDataRepository extends $Notifier<void> {
   void build();

apps/weblibre/test/drift/tabs/tab_hierarchy_order_test.dart

@@ -0,0 +1,133 @@
+import 'package:drift/drift.dart';
+import 'package:drift/native.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:lexo_rank/lexo_rank.dart';
+import 'package:weblibre/data/database/functions/lexo_rank_functions.dart';
+import 'package:weblibre/data/database/functions/url_functions.dart';
+import 'package:weblibre/features/geckoview/features/tabs/data/database/database.dart';
+
+void main() {
+  late TabDatabase db;
+
+  setUp(() {
+    db = TabDatabase(
+      NativeDatabase.memory(
+        setup: (database) {
+          registerLexorankFunctions(database);
+          registerUrlFunctions(database);
+        },
+      ),
+    );
+  });
+
+  tearDown(() async {
+    await db.close();
+  });
+
+  test('setTabParent appends after the existing last child subtree', () async {
+    await _insertTabs(db, const [
+      _TabFixture('parent'),
+      _TabFixture('existing-child', parentId: 'parent'),
+      _TabFixture('existing-grandchild', parentId: 'existing-child'),
+      _TabFixture('moving'),
+      _TabFixture('moving-child', parentId: 'moving'),
+    ]);
+
+    final moved = await db.tabDao.setTabParent(
+      tabId: 'moving',
+      newParentId: 'parent',
+    );
+
+    expect(moved, isTrue);
+    expect(await _orderedTabIds(db), [
+      'parent',
+      'existing-child',
+      'existing-grandchild',
+      'moving',
+      'moving-child',
+    ]);
+  });
+
+  test(
+    'promoteChildToParent demotes after the promoted child subtree',
+    () async {
+      await _insertTabs(db, const [
+        _TabFixture('parent'),
+        _TabFixture('child', parentId: 'parent'),
+        _TabFixture('grandchild', parentId: 'child'),
+        _TabFixture('great-grandchild', parentId: 'grandchild'),
+      ]);
+
+      final promoted = await db.tabDao.promoteChildToParent('child');
+
+      expect(promoted, isTrue);
+      expect(await _orderedTabIds(db), [
+        'child',
+        'grandchild',
+        'great-grandchild',
+        'parent',
+      ]);
+    },
+  );
+
+  test(
+    'moveTabAmongSiblings moves down after the target sibling subtree',
+    () async {
+      await _insertTabs(db, const [
+        _TabFixture('parent'),
+        _TabFixture('first', parentId: 'parent'),
+        _TabFixture('first-child', parentId: 'first'),
+        _TabFixture('second', parentId: 'parent'),
+        _TabFixture('second-child', parentId: 'second'),
+      ]);
+
+      final moved = await db.tabDao.moveTabAmongSiblings('first', down: true);
+
+      expect(moved, isTrue);
+      expect(await _orderedTabIds(db), [
+        'parent',
+        'second',
+        'second-child',
+        'first',
+        'first-child',
+      ]);
+    },
+  );
+}
+
+Future<void> _insertTabs(TabDatabase db, List<_TabFixture> tabs) async {
+  final orderKeys = _spacedOrderKeys(tabs.length);
+
+  for (final (index, tab) in tabs.indexed) {
+    await db.tabDao.upsertTabTransactional(
+      () async => tab.id,
+      parentId: Value(tab.parentId),
+      orderKey: Value(orderKeys[index]),
+    );
+  }
+}
+
+Future<List<String>> _orderedTabIds(TabDatabase db) {
+  return db.tabDao.getAllTabIds().get();
+}
+
+List<String> _spacedOrderKeys(int count) {
+  var rank = LexoRank.middle();
+  final orderKeys = <String>[];
+
+  for (var i = 0; i < count; i++) {
+    orderKeys.add(rank.value);
+    for (var gap = 0; gap < 4; gap++) {
+      rank = rank.genNext();
+    }
+  }
+
+  return orderKeys;
+}
+
+class _TabFixture {
+  final String id;
+  final String? parentId;
+
+  const _TabFixture(this.id, {this.parentId});
+}