Make the shell top bar hide/reveal with scroll, per tab

Each regular tab (Files/Photos/Favorites/Shares/Recent/Activity/Trash)
now plants its own AppTopBar as the first sliver in its own
CustomScrollView, via a new topBarSliver() helper (tab_state_slivers.dart)
wrapping the framework's SliverFloatingHeader, instead of one shared
instance living in Scaffold.appBar.

This gives each tab's top bar Material's native floating-app-bar
behavior - tied to that tab's own ScrollController - scrolling away as
the list scrolls down and reappearing the moment the drag reverses,
not only once scrolled all the way back to the top, which a single
fixed Scaffold.appBar (or the "put it in a SliverToBoxAdapter" escape
hatch NooTopBar's doc comment already mentioned) can't do. It sits
above each tab's own pinned in-content sticky header (the sort/filter
row, or the selection bar that replaces it), which keeps working
unchanged underneath it.

main.dart builds a separate, correctly-labelled AppTopBar per tab
(rather than one for "whichever tab is selected") and passes it through
buildAppTabView's new optional topBar parameter; it's null on desktop
(which keeps its own NooToolbar) and while picking, matching the old
Scaffold.appBar: pickRequest == null guard.

SliverFloatingHeader sizes itself from the bar's own natural layout
(like SliverToBoxAdapter) rather than a fixed extent declared up front,
so NooTopBar's own internal SafeArea keeps handling the status-bar inset
correctly with no extra height math needed on this side.

Adds a widget test (test/widgets/tabs/tab_state_slivers_test.dart)
driving a raw gesture mid-drag to verify the reveal-follows-finger
behavior, since a single tester.drag() only pumps after the gesture -
including release - has already finished, which doesn't exercise the
live per-frame reveal this change depends on.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

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);