.claude/context/architecture.md

@@ -284,7 +284,21 @@ bare system prompt gives no context on its own.
   other tab has a create/upload flow), and the account avatar; Android
   gets a compact title row with `search`/avatar actions, relying on an
   extended `NooFab` ("Upload", Files/Photos only) instead of a top-bar
-  icon for upload. `BottomNavBar` (`widgets/bottom_nav_bar.dart`) adapts
+  icon for upload. Rather than one shared instance in `Scaffold.appBar`,
+  `MainShellView` builds a separate `AppTopBar` per tab (labelled for that
+  tab) and each tab plants its own as the first sliver in its own
+  `CustomScrollView` (`topBarSliver` in `widgets/tabs/tab_state_slivers.dart`,
+  wrapping it in the framework's `SliverFloatingHeader`) instead of passing
+  it to `Scaffold.appBar` - see that file's doc comment for why (Material's
+  native "floating" app bar behavior, tied to that tab's own
+  `ScrollController`: scrolls away as the list scrolls down and reappears
+  the moment the drag reverses, not only once scrolled back to the top).
+  `topBar` is null (no top bar rendered) on desktop and while picking,
+  matching `Scaffold.appBar`'s old `pickRequest == null` guard - see
+  `buildAppTabView`'s doc comment. It sits above each tab's own pinned
+  in-content header (the sort/filter controls row, or Files/Photos'
+  selection bar - see below); the two float/scroll independently.
+  `BottomNavBar` (`widgets/bottom_nav_bar.dart`) adapts
   the pinned `AppTab`s onto `NooBottomBar`. `AppDrawer`
   (`widgets/app_drawer.dart`) builds a `NooDrawer`: account block, storage
   meter, a "More" list of the hidden tabs, Settings, and an "Edit tabs"

.claude/context/styling.md

@@ -137,6 +137,12 @@ blocks are noted where they matter:
   `lib/widgets/tabs/` (`tab_state_slivers.dart`, `tab_day_groups.dart`,
   `tab_location.dart`) — the loading/error/empty-state slivers and
   day/month grouping helpers shared by Recent/Activity/Trash/Shares.
+  `tab_state_slivers.dart` also has `topBarSliver`, which every regular
+  tab's view uses to plant its own `AppTopBar` instance as the first sliver
+  in its `CustomScrollView` (a thin wrapper around the framework's
+  `SliverFloatingHeader`) instead of the shell passing one shared instance
+  to `Scaffold.appBar` - see its doc comment and `architecture.md`'s
+  "Mobile" bullet for why.
   `lib/widgets/settings/` — Settings' 8 section widgets plus
   `settings_section.dart`'s `SettingsSection`/`showSettingsPicker` and
   `settings_dialogs.dart`'s `confirmRemoveAccount`.

lib/main.dart

@@ -381,15 +381,51 @@ class _MainShellViewState extends State<MainShellView> {
     String? trashBadge(AppTab tab) =>
         tab == AppTab.trash && trashCount > 0 ? '$trashCount' : null;
 
+    final isDesktop = NooLayout.isDesktop(context);
+    final navStyle = NooLayout.navStyle(context);
+    // Picking/offline already override the tab set itself (see pinnedTabs
+    // above) - Search doesn't belong in either: there's nothing to search
+    // for a file-picking flow, and Search needs the network Offline mode
+    // doesn't have.
+    final showBottomBarSearch = !overrideActive && settings.searchInBottomBar;
+
     // Each tab renders its own sticky selection toolbar inline (right under
     // its sort/filter row) instead of the shell swapping in a shared one,
     // so the nav chrome stays put and usable regardless of selection state.
+    //
+    // Each tab also builds its own [AppTopBar] (labelled for that tab, not
+    // just whichever is currently selected) and plants it as that tab's own
+    // first sliver - see `buildAppTabView`'s doc comment and `topBarSliver`
+    // in `tabs/tab_state_slivers.dart` - instead of one shared instance
+    // living in `Scaffold.appBar`. That's what gives each tab's top bar
+    // Material's native floating-away-on-scroll-down/reappear-on-scroll-up
+    // behavior, tied to that tab's own `ScrollController`: a fixed
+    // `Scaffold.appBar` can't do that (no per-tab scroll signal reaches
+    // it), and a shared single instance can't show 7 different tab labels
+    // at once now that every tab keeps its own independent scroll state.
+    // Null on desktop (which shows `NooToolbar` instead - embedding it here
+    // too, since `tabStack` is shared by both layouts below, would double
+    // up the top chrome there) and while picking (no top bar at all, same
+    // as this screen's old `Scaffold.appBar: pickRequest == null ? ... :
+    // null`).
     final tabStack = Stack(
       children: [
         IndexedStack(
           index: selectedIndex,
           children: displayTabs
-              .map((tab) => buildAppTabView(tab, _scrollControllers[tab]!))
+              .map(
+                (tab) => buildAppTabView(
+                  tab,
+                  _scrollControllers[tab]!,
+                  topBar: isDesktop || pickRequest != null
+                      ? null
+                      : AppTopBar(
+                          style: navStyle,
+                          tab: tab,
+                          searchInBottomBar: showBottomBarSearch,
+                        ),
+                ),
+              )
               .toList(),
         ),
         if (pick.isDownloadingForPick) const _PickingProgressOverlay(),
@@ -401,7 +437,7 @@ class _MainShellViewState extends State<MainShellView> {
         (selectedTab == AppTab.files || selectedTab == AppTab.photos);
 
     Widget scaffold;
-    if (NooLayout.isDesktop(context)) {
+    if (isDesktop) {
       scaffold = Scaffold(
         backgroundColor: colors.bg,
         body: Row(
@@ -471,23 +507,11 @@ class _MainShellViewState extends State<MainShellView> {
         ),
       );
     } else {
-      final navStyle = NooLayout.navStyle(context);
       final bottomBarStyle = settings.bottomBarStyle;
-      // Picking/offline already override the tab set itself (see
-      // pinnedTabs above) - Search doesn't belong in either: there's
-      // nothing to search for a file-picking flow, and Search needs the
-      // network Offline mode doesn't have.
-      final showBottomBarSearch = !overrideActive && settings.searchInBottomBar;
       scaffold = Scaffold(
         backgroundColor: colors.bg,
         drawerScrimColor: colors.scrim,
-        appBar: pickRequest == null
-            ? AppTopBar(
-                style: navStyle,
-                tab: selectedTab,
-                searchInBottomBar: showBottomBarSearch,
-              )
-            : null,
+        // The top bar itself no longer lives here - see `tabStack` above.
         drawer: pickRequest == null ? const AppDrawer() : null,
         // Floating needs the body to draw behind the bar's own transparent
         // margin (see NooBottomBarStyle's doc comment) instead of stopping

lib/views/activity_view.dart

@@ -29,7 +29,11 @@ import '../widgets/tabs/tab_state_slivers.dart';
 class ActivityView extends StatelessWidget {
   final ScrollController scrollController;
 
-  const ActivityView({super.key, required this.scrollController});
+  /// This tab's own shell top bar, planted as its first sliver - see
+  /// `buildAppTabView`'s doc comment. Null on desktop and while picking.
+  final PreferredSizeWidget? topBar;
+
+  const ActivityView({super.key, required this.scrollController, this.topBar});
 
   @override
   Widget build(BuildContext context) {
@@ -90,6 +94,7 @@ class ActivityView extends StatelessWidget {
     }
 
     final List<Widget> contentSlivers = [
+      if (topBar != null) topBarSliver(topBar!),
       const SliverToBoxAdapter(child: SizedBox(height: NooSpace.md)),
       feed,
       ...tabBottomInsetSlivers,

lib/views/favorites_view.dart

@@ -30,6 +30,7 @@ import '../widgets/noo/core/noo_button.dart';
 import '../widgets/share_sheet.dart';
 import '../widgets/sticky_header_delegate.dart';
 import '../widgets/synced_header_scaffold.dart' show formatBytes;
+import '../widgets/tabs/tab_state_slivers.dart';
 import 'file_viewer_screen.dart';
 import 'move_copy_destination_picker.dart';
 
@@ -50,7 +51,11 @@ import 'move_copy_destination_picker.dart';
 class FavoritesView extends StatefulWidget {
   final ScrollController scrollController;
 
-  const FavoritesView({super.key, required this.scrollController});
+  /// This tab's own shell top bar, planted as its first sliver - see
+  /// `buildAppTabView`'s doc comment. Null on desktop and while picking.
+  final PreferredSizeWidget? topBar;
+
+  const FavoritesView({super.key, required this.scrollController, this.topBar});
 
   @override
   State<FavoritesView> createState() => _FavoritesViewState();
@@ -507,6 +512,7 @@ class _FavoritesViewState extends State<FavoritesView> {
     );
 
     final contentSlivers = <Widget>[
+      if (widget.topBar != null) topBarSliver(widget.topBar!),
       SliverPersistentHeader(
         pinned: !_isSelecting,
         delegate: StickyHeaderDelegate(

lib/views/files_view.dart

@@ -43,6 +43,7 @@ import '../widgets/noo/noo_layout.dart';
 import '../widgets/noo/overlays/noo_sheet.dart';
 import '../widgets/share_sheet.dart';
 import '../widgets/sticky_header_delegate.dart';
+import '../widgets/tabs/tab_state_slivers.dart';
 import '../widgets/synced_header_scaffold.dart' show formatBytes;
 import 'file_viewer_screen.dart';
 import 'move_copy_destination_picker.dart';
@@ -59,10 +60,15 @@ class FilesView extends StatefulWidget {
   final ScrollController scrollController;
   final bool offline;
 
+  /// This tab's own shell top bar, planted as its first sliver - see
+  /// `buildAppTabView`'s doc comment. Null on desktop and while picking.
+  final PreferredSizeWidget? topBar;
+
   const FilesView({
     super.key,
     required this.scrollController,
     this.offline = false,
+    this.topBar,
   });
 
   @override
@@ -653,6 +659,7 @@ class _FilesViewState extends State<FilesView> {
           );
 
     final List<Widget> contentSlivers = [
+      if (widget.topBar != null) topBarSliver(widget.topBar!),
       // Pinned in both states - while browsing this is the controls row
       // (+ breadcrumbs), while selecting it's the selection bar (see
       // `topRow` above): either way it's the one thing that always stays

lib/views/photos_view.dart

@@ -30,6 +30,7 @@ import '../widgets/noo/overlays/noo_sheet.dart';
 import '../widgets/share_sheet.dart';
 import '../widgets/sort_menu_button.dart' show sortFieldLabel;
 import '../widgets/sticky_header_delegate.dart';
+import '../widgets/tabs/tab_state_slivers.dart';
 import 'file_viewer_screen.dart';
 import 'move_copy_destination_picker.dart';
 
@@ -53,7 +54,11 @@ class _MonthGroup {
 class PhotosView extends StatefulWidget {
   final ScrollController scrollController;
 
-  const PhotosView({super.key, required this.scrollController});
+  /// This tab's own shell top bar, planted as its first sliver - see
+  /// `buildAppTabView`'s doc comment. Null on desktop and while picking.
+  final PreferredSizeWidget? topBar;
+
+  const PhotosView({super.key, required this.scrollController, this.topBar});
 
   @override
   State<PhotosView> createState() => _PhotosViewState();
@@ -239,6 +244,7 @@ class _PhotosViewState extends State<PhotosView> {
     );
 
     final List<Widget> contentSlivers = [
+      if (widget.topBar != null) topBarSliver(widget.topBar!),
       // Sticky while browsing; once selecting, the selection bar takes over
       // the same slot instead.
       SliverPersistentHeader(

lib/views/recent_view.dart

@@ -27,7 +27,11 @@ import 'file_viewer_screen.dart';
 class RecentView extends StatefulWidget {
   final ScrollController scrollController;
 
-  const RecentView({super.key, required this.scrollController});
+  /// This tab's own shell top bar, planted as its first sliver - see
+  /// `buildAppTabView`'s doc comment. Null on desktop and while picking.
+  final PreferredSizeWidget? topBar;
+
+  const RecentView({super.key, required this.scrollController, this.topBar});
 
   @override
   State<RecentView> createState() => _RecentViewState();
@@ -54,6 +58,7 @@ class _RecentViewState extends State<RecentView> {
     );
 
     final List<Widget> contentSlivers = [
+      if (widget.topBar != null) topBarSliver(widget.topBar!),
       const SliverToBoxAdapter(child: SizedBox(height: NooSpace.md)),
       if (recent.isLoading && items.isEmpty)
         tabLoadingSliver

lib/views/shares_view.dart

@@ -53,7 +53,11 @@ String _permissionLabel(int permissions) {
 class SharesView extends StatefulWidget {
   final ScrollController scrollController;
 
-  const SharesView({super.key, required this.scrollController});
+  /// This tab's own shell top bar, planted as its first sliver - see
+  /// `buildAppTabView`'s doc comment. Null on desktop and while picking.
+  final PreferredSizeWidget? topBar;
+
+  const SharesView({super.key, required this.scrollController, this.topBar});
 
   @override
   State<SharesView> createState() => _SharesViewState();
@@ -81,6 +85,7 @@ class _SharesViewState extends State<SharesView> {
     final isDesktop = NooLayout.isDesktop(context);
 
     final List<Widget> contentSlivers = [
+      if (widget.topBar != null) topBarSliver(widget.topBar!),
       SliverPadding(
         padding: EdgeInsets.fromLTRB(
           NooLayout.gutter(context),

lib/views/trash_view.dart

@@ -25,7 +25,11 @@ import '../widgets/tabs/tab_state_slivers.dart';
 class TrashView extends StatefulWidget {
   final ScrollController scrollController;
 
-  const TrashView({super.key, required this.scrollController});
+  /// This tab's own shell top bar, planted as its first sliver - see
+  /// `buildAppTabView`'s doc comment. Null on desktop and while picking.
+  final PreferredSizeWidget? topBar;
+
+  const TrashView({super.key, required this.scrollController, this.topBar});
 
   @override
   State<TrashView> createState() => _TrashViewState();
@@ -50,6 +54,7 @@ class _TrashViewState extends State<TrashView> {
     final isDesktop = NooLayout.isDesktop(context);
 
     final List<Widget> contentSlivers = [
+      if (widget.topBar != null) topBarSliver(widget.topBar!),
       SliverPadding(
         padding: EdgeInsets.fromLTRB(
           NooLayout.gutter(context),

lib/widgets/app_tab_view_builder.dart

@@ -11,7 +11,20 @@ import '../views/trash_view.dart';
 /// Builds the view widget for a given [AppTab]. Shared by the main shell
 /// (for visible tabs) and the "more tabs" dropdown (for launching a tab
 /// that's currently hidden from the bottom nav bar).
-Widget buildAppTabView(AppTab tab, ScrollController controller) {
+///
+/// [topBar], when given, is that tab's own [AppTopBar] instance (built by
+/// the caller, which owns `NooLayout.navStyle`/pick-mode/search-in-bottom-
+/// bar state) - each view plants it as its own first sliver (see
+/// `topBarSliver` in `tabs/tab_state_slivers.dart`) so it scrolls away and
+/// reappears independently, tied to that tab's own `ScrollController`
+/// rather than living in the shared `Scaffold.appBar`. Null on desktop
+/// (which shows `NooToolbar` instead) and while picking (no top bar at
+/// all), matching `Scaffold.appBar`'s old `pickRequest == null` guard.
+Widget buildAppTabView(
+  AppTab tab,
+  ScrollController controller, {
+  PreferredSizeWidget? topBar,
+}) {
   switch (tab) {
     case AppTab.files:
       // Keyed so the Files and Offline tabs (same widget type) never share
@@ -19,24 +32,26 @@ Widget buildAppTabView(AppTab tab, ScrollController controller) {
       return FilesView(
         key: const ValueKey('files'),
         scrollController: controller,
+        topBar: topBar,
       );
     case AppTab.photos:
-      return PhotosView(scrollController: controller);
+      return PhotosView(scrollController: controller, topBar: topBar);
     case AppTab.favorites:
-      return FavoritesView(scrollController: controller);
+      return FavoritesView(scrollController: controller, topBar: topBar);
     case AppTab.activity:
-      return ActivityView(scrollController: controller);
+      return ActivityView(scrollController: controller, topBar: topBar);
     case AppTab.trash:
-      return TrashView(scrollController: controller);
+      return TrashView(scrollController: controller, topBar: topBar);
     case AppTab.shares:
-      return SharesView(scrollController: controller);
+      return SharesView(scrollController: controller, topBar: topBar);
     case AppTab.recent:
-      return RecentView(scrollController: controller);
+      return RecentView(scrollController: controller, topBar: topBar);
     case AppTab.offline:
       return FilesView(
         key: const ValueKey('offline'),
         scrollController: controller,
         offline: true,
+        topBar: topBar,
       );
   }
 }

lib/widgets/tabs/tab_state_slivers.dart

@@ -94,3 +94,29 @@ const List<Widget> tabBottomInsetSlivers = [
   SliverToBoxAdapter(child: SizedBox(height: 100)),
   SliverFillRemaining(hasScrollBody: false, child: SizedBox()),
 ];
+
+/// Wraps a tab's shell top bar ([AppTopBar], passed in as the generic
+/// [PreferredSizeWidget] it implements - this file can't import
+/// `app_top_bar.dart` without a cycle) as that tab's own first sliver,
+/// living inside its `CustomScrollView` instead of `Scaffold.appBar`. Gives
+/// it Material's native "floating app bar" behavior, via the framework's own
+/// [SliverFloatingHeader]: it scrolls away as the list scrolls down, and -
+/// unlike a plain `SliverToBoxAdapter`, which only reappears once scrolled
+/// all the way back to the top - reappears immediately on any upward
+/// scroll, following the finger while dragging and settling fully open or
+/// fully closed once the gesture ends.
+///
+/// [SliverFloatingHeader] sizes itself from [topBar]'s own natural layout
+/// (like `SliverToBoxAdapter`) rather than a fixed extent declared up
+/// front - so [topBar]'s own internal `SafeArea` (see `NooTopBar`'s doc
+/// comment) already accounts for the status-bar inset correctly, with no
+/// extra height math needed here (unlike building this on the general-
+/// purpose `SliverPersistentHeader` would have required).
+///
+/// Sits above a tab's own pinned in-content header (built with
+/// [StickyHeaderDelegate] - the sort/filter controls row, or the selection
+/// bar that replaces it) - put this sliver first in `contentSlivers` so
+/// that header stays exactly where it already is, independent of whether
+/// [topBar] is currently shown or scrolled away.
+Widget topBarSliver(PreferredSizeWidget topBar) =>
+    SliverFloatingHeader(child: topBar);

test/widgets/tabs/tab_state_slivers_test.dart

@@ -0,0 +1,143 @@
+import 'package:flutter/material.dart';
+import 'package:flutter/rendering.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:noo/widgets/tabs/tab_state_slivers.dart';
+
+import '../noo/noo_test_utils.dart';
+
+/// A minimal stand-in for `AppTopBar` - just needs to be a fixed-height
+/// [PreferredSizeWidget], same contract `topBarSliver` wraps in real tabs.
+class _FakeTopBar extends StatelessWidget implements PreferredSizeWidget {
+  const _FakeTopBar();
+
+  static const double height = 56;
+
+  @override
+  Size get preferredSize => const Size.fromHeight(height);
+
+  @override
+  Widget build(BuildContext context) => const SizedBox(
+    height: height,
+    child: ColoredBox(color: Colors.blue),
+  );
+}
+
+/// Matches the one sliver `topBarSliver` inserts, even once it's fully
+/// scrolled away - `find.byType`'s default `skipOffstage: true` treats a
+/// sliver with `geometry.visible == false` (paintExtent 0, exactly the
+/// "fully hidden" state part of this test exercises) as offstage and
+/// excludes it, which would otherwise make `tester.renderObject` throw
+/// instead of reporting the 0 this test expects. A function, not a
+/// top-level constant, so each call re-evaluates against whichever widget
+/// tree is currently pumped.
+Finder _header() => find.byType(SliverFloatingHeader, skipOffstage: false);
+
+Future<void> _pumpHost(WidgetTester tester, ScrollController controller) {
+  return tester.pumpWidget(
+    MaterialApp(
+      theme: nooTheme(Brightness.light),
+      home: Scaffold(
+        body: CustomScrollView(
+          controller: controller,
+          slivers: [
+            topBarSliver(const _FakeTopBar()),
+            SliverList(
+              delegate: SliverChildBuilderDelegate(
+                (context, index) =>
+                    SizedBox(height: 60, child: Text('Item $index')),
+                childCount: 40,
+              ),
+            ),
+          ],
+        ),
+      ),
+    ),
+  );
+}
+
+void main() {
+  setUpNooTests();
+
+  testWidgets(
+    'topBarSliver floats away scrolling down and reappears the moment the '
+    'drag reverses, not only once back at the top (Material floating app '
+    'bar behavior)',
+    (tester) async {
+      final controller = ScrollController();
+      addTearDown(controller.dispose);
+      await _pumpHost(tester, controller);
+
+      // The render object's own `geometry.paintExtent` is the ground truth
+      // for how much of the bar is actually visible - more reliable than
+      // inferring visibility from hit-testing/finding the child, which a
+      // floating header sliver keeps built regardless of paint extent.
+      double paintExtent() =>
+          tester.renderObject<RenderSliver>(_header()).geometry!.paintExtent;
+
+      // Fully visible before any scroll.
+      expect(paintExtent(), _FakeTopBar.height);
+      expect(controller.offset, 0);
+
+      // Drive one continuous drag by hand (rather than `tester.drag`, which
+      // only pumps once the whole gesture - including the final pointer-up
+      // - has already finished): the floating header's reveal-while-
+      // dragging behavior keys off the *live* scroll direction as reported
+      // mid-gesture, so this needs an intermediate pump while the pointer
+      // is still down to actually observe it.
+      final gesture = await tester.startGesture(const Offset(200, 300));
+
+      // Drag up (content scrolls down) well past the bar's own height, so
+      // it scrolls fully away, same as a plain `SliverToBoxAdapter` would.
+      await gesture.moveBy(const Offset(0, -200));
+      await tester.pump();
+
+      expect(paintExtent(), 0);
+      final scrolledOffset = controller.offset;
+      expect(
+        scrolledOffset,
+        greaterThan(_FakeTopBar.height),
+        reason: "the drag should have moved past the bar's own height",
+      );
+
+      // Reverse direction by a small amount, still mid-gesture and nowhere
+      // near the top of the list. A plain `SliverToBoxAdapter`, or a header
+      // that only reappears once back at the top, would stay fully hidden
+      // here. The floating bar should start reappearing immediately
+      // instead, following the drag.
+      await gesture.moveBy(const Offset(0, 40));
+      await tester.pump();
+
+      expect(controller.offset, lessThan(scrolledOffset));
+      expect(
+        controller.offset,
+        greaterThan(_FakeTopBar.height / 2),
+        reason: 'still far from the top of the list',
+      );
+      expect(
+        paintExtent(),
+        greaterThan(0),
+        reason:
+            'the bar should already be reappearing on the first upward '
+            'movement, without needing to reach the top',
+      );
+
+      await gesture.up();
+      await tester.pumpAndSettle();
+    },
+  );
+
+  testWidgets(
+    "topBarSliver sizes itself from the wrapped bar's own layout (e.g. its "
+    'SafeArea-padded height), not a value declared up front',
+    (tester) async {
+      final controller = ScrollController();
+      addTearDown(controller.dispose);
+      await _pumpHost(tester, controller);
+
+      expect(
+        tester.getSize(find.byType(_FakeTopBar)).height,
+        _FakeTopBar.height,
+      );
+    },
+  );
+}