Restructure step 0: test safety net, AppEvent/Notifier seam, platform ports, protocol 16 planned

- Tests: the four known failures fixed (test-side causes), one duplicate
  file and four detail-pinning cases removed, every test that pins
  behaviour the restructure changes tagged with its step.
- Every toast, sound and activity-log line goes through Notifier.notify
  (AppEvent), mapped one-to-one to today's behaviour.
- Platform ports (shell, URLs, folders, link resolver, system
  notifications) with desktop implementations; window_manager, Process
  and file_picker now live only in platform/desktop/.
- ROADMAP: protocol 16 planned; app id dev.foxyz.starsync.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/desktop/lib/src/shell/app_shell.dart

@@ -3,9 +3,7 @@ import 'dart:io' show File;
 
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
-import 'package:fox_utils/fox_utils.dart' show ClipboardX, DesktopDropX, DropTarget;
 import 'package:signals/signals_flutter.dart';
-import 'package:window_manager/window_manager.dart';
 
 import '../controls/frame.dart' show DoubleClickListener;
 import '../files/folder_store.dart';
@@ -14,6 +12,7 @@ import '../jellyfin/accounts.dart';
 import '../jellyfin/browse_scope.dart' show BrowseStart;
 import '../jellyfin/session_media.dart';
 import '../screens/home/connect_flow.dart';
+import '../session/app_events.dart' show ActionFailed, ScheduleResult;
 import '../session/session_coordinator.dart' show ConnectParams;
 import '../screens/home/health_probe.dart';
 import '../screens/home/media_picker.dart';
@@ -25,6 +24,7 @@ import '../update/update_controller.dart';
 import 'chat_panel.dart';
 import 'connect_cards.dart';
 import 'handoff.dart';
+import 'library_link.dart' show LinkProber, defaultLinkProber;
 import 'library_tab.dart';
 import 'motion.dart';
 import 'party_strip.dart';
@@ -58,6 +58,9 @@ class AppShell extends StatefulWidget {
   final JellyfinAccounts? jellyfin;
   /// Stand-in for media_kit's `Video` (tests).
   final VideoViewBuilder? videoBuilder;
+  /// What the Library's Link page asks about a link (tests: a fake, so no
+  /// network or yt-dlp runs).
+  final LinkProber linkProbe;
   const AppShell({
     super.key,
     this.updates,
@@ -66,6 +69,7 @@ class AppShell extends StatefulWidget {
     this.healthGet = defaultHealthGet,
     this.jellyfin,
     this.videoBuilder,
+    this.linkProbe = defaultLinkProber,
   });
 
   @override
@@ -329,7 +333,7 @@ class AppShellState extends State<AppShell> with SingleTickerProviderStateMixin
   Future<void> _setWindowFullscreen(bool on) async {
     if (!widget.windowControls) return;
     try {
-      await windowManager.setFullScreen(on);
+      await SessionState.instance.ports.shell.setFullScreen(on);
     } catch (_) {
       // No window manager.
     }
@@ -457,17 +461,8 @@ class AppShellState extends State<AppShell> with SingleTickerProviderStateMixin
   /// Clipboard files first, then text (a link or absolute paths). A pasted
   /// image has no taker yet, so the clipboard's image data is not read.
   Future<void> _paste() async {
-    var files = const <String>[];
-    String? text;
-    try {
-      files = await ClipboardX.readFiles();
-    } catch (_) {}
-    if (files.isEmpty) {
-      try {
-        text = await ClipboardX.readText();
-      } catch (_) {}
-    }
-    await _handOff(classifyHandoff(paths: files, text: text), _pointer);
+    final clip = await SessionState.instance.ports.shell.readPaste();
+    await _handOff(classifyHandoff(paths: clip.files, text: clip.text), _pointer);
   }
 
   Future<void> _handOff(Handoff item, Offset? at) async {
@@ -489,7 +484,7 @@ class AppShellState extends State<AppShell> with SingleTickerProviderStateMixin
       case (HandoffVideos(:final paths), HandoffAction.putUp):
         final error = await _putUp(FileMedia(paths.first));
         if (error != null) {
-          SessionState.instance.coordinator.showToast(error);
+          SessionState.instance.coordinator.notify(ActionFailed(error));
         } else {
           await FolderStore.instance.ensureLoaded();
           FolderStore.instance.addRecent(paths.first);
@@ -500,7 +495,7 @@ class AppShellState extends State<AppShell> with SingleTickerProviderStateMixin
         for (final p in next ? paths.reversed : paths) {
           final error = await SessionState.instance.coordinator.queue.add(FileMedia(p), next: next);
           if (error != null) {
-            SessionState.instance.coordinator.showToast(error);
+            SessionState.instance.coordinator.notify(ActionFailed(error));
             break;
           }
         }
@@ -509,7 +504,7 @@ class AppShellState extends State<AppShell> with SingleTickerProviderStateMixin
         final coord = SessionState.instance.coordinator;
         final error = await coord.queue
             .add(LinkMedia(url, relay: _picker.linkRelay), next: action == HandoffAction.playNext);
-        if (error != null) coord.showToast(error);
+        if (error != null) coord.notify(ActionFailed(error));
       case (HandoffVideos(:final paths), HandoffAction.addFolder):
         await _addFolder(File(paths.first).parent.path);
       case (HandoffFolder(:final path), _):
@@ -540,13 +535,13 @@ class AppShellState extends State<AppShell> with SingleTickerProviderStateMixin
   }
 
   // Off on Settings: its own drop targets (cookies) take the files there.
-  Widget _dropTarget(Widget child) => DropTarget(
+  Widget _dropTarget(Widget child) => SessionState.instance.ports.shell.dropTarget(
         enable: _tab != ShellTab.settings,
-        onDragEntered: (_) => setState(() => _dragging = _onTop),
-        onDragExited: (_) => setState(() => _dragging = false),
-        onDragDone: (d) {
+        onEnter: () => setState(() => _dragging = _onTop),
+        onExit: () => setState(() => _dragging = false),
+        onDrop: (paths, at) {
           setState(() => _dragging = false);
-          _handOff(classifyHandoff(paths: DesktopDropX.pathsOf(d.files)), d.localPosition);
+          _handOff(classifyHandoff(paths: paths), at);
         },
         child: Stack(
           fit: StackFit.expand,
@@ -718,12 +713,13 @@ class AppShellState extends State<AppShell> with SingleTickerProviderStateMixin
           // Up next needs a server (a solo session has one).
           onAddToQueue: online ? coord.queue.add : null,
           onOpenIntegrations: () => _openSettings(SettingsSection.integrations),
+          probe: widget.linkProbe,
         ),
       ShellTab.schedule => SchedulePage(
           solo: alone,
           onPutUp: _putUp,
           onAddToQueue: online ? coord.queue.add : null,
-          onToast: coord.showToast,
+          onToast: (text) => coord.notify(ScheduleResult(text)),
         ),
       ShellTab.settings => SettingsTab(
           section: _section,

apps/desktop/lib/src/shell/library_link.dart

@@ -6,11 +6,11 @@ import 'package:flutter/services.dart';
 import 'package:sync_relay_core/core.dart'
     show LinkProbe, hasMediaExtension, parseJellyfinLink, playErrorText, unreachableText;
 
-import '../playback/yt_dlp_app.dart';
 import '../screens/home/media_picker.dart';
 import '../widgets/app_menu.dart';
 import '../widgets/copy_open.dart';
 import '../state/connect_prefs.dart';
+import '../state/session_state.dart';
 import 'motion.dart';
 
 // The Library's Link source: a big paste field, a preview of what the link
@@ -236,10 +236,10 @@ class LinkPreviewStore {
   }
 }
 
-/// What a link is (see [AppYtDlp.probe]).
+/// What a link is (see [LinkResolver.probe]).
 typedef LinkProber = Future<LinkProbe> Function(String url);
 
-Future<LinkProbe> defaultLinkProber(String url) => AppYtDlp.instance.probe(url);
+Future<LinkProbe> defaultLinkProber(String url) => SessionState.instance.ports.links.probe(url);
 
 String _host(Uri uri) => uri.host.startsWith('www.') ? uri.host.substring(4) : uri.host;
 

apps/desktop/lib/src/shell/mark_problem.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:sync_relay_core/core.dart' show RelayConstants;
 
+import '../session/app_events.dart' show ProblemMarked;
 import '../state/session_state.dart';
 import '../widgets/app_menu.dart' show AppGlass;
 import 'motion.dart';
@@ -19,7 +20,7 @@ Future<void> showMarkProblem(BuildContext context) async {
   if (note == null) return;
   final coord = SessionState.instance.coordinator;
   final inSession = await coord.markProblem(note);
-  coord.showToast(inSession ? 'Marked in the session log' : "Marked in this app's log");
+  coord.notify(ProblemMarked(inSession: inSession));
 }
 
 /// The small card: a one-line note and Mark. Pops with the note (maybe

apps/desktop/lib/src/shell/party_strip.dart

@@ -3,7 +3,6 @@ import 'dart:io';
 import 'package:flutter/material.dart';
 import 'package:signals/signals_flutter.dart';
 import 'package:sync_relay_core/core.dart';
-import 'package:window_manager/window_manager.dart';
 
 import '../screens/home/ui.dart' show appName, displayVersion, shortVersion;
 import '../session/delivery.dart';
@@ -263,7 +262,7 @@ class PartyStrip extends StatelessWidget {
             // their own clicks.
             if (windowControls)
               const Positioned.fill(
-                child: DragToMoveArea(child: SizedBox.expand()),
+                child: WindowDragArea(child: SizedBox.expand()),
               ),
             Positioned.fill(child: row),
           ],

apps/desktop/lib/src/shell/profile_card.dart

@@ -3,7 +3,6 @@ import 'dart:math' as math;
 import 'dart:typed_data';
 import 'dart:ui' as ui;
 
-import 'package:file_picker/file_picker.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 import 'package:signals/signals_flutter.dart';
@@ -329,18 +328,17 @@ class _CropPickerState extends State<CropPicker> {
   }
 
   Future<void> _pick() async {
-    final List<PlatformFile> files;
+    final List<String> files;
     try {
-      files = await FilePicker.pickFiles(
+      files = await SessionState.instance.ports.folders.pickFiles(
         dialogTitle: 'Pick a picture',
-        type: FileType.custom,
-        allowedExtensions: const ['png', 'jpg', 'jpeg', 'webp', 'gif', 'bmp'],
+        extensions: const ['png', 'jpg', 'jpeg', 'webp', 'gif', 'bmp'],
       );
     } catch (e) {
       if (mounted) setState(() => _error = 'file dialog unavailable — try again');
       return;
     }
-    final path = files.isEmpty ? null : files.first.path;
+    final path = files.firstOrNull;
     if (path == null) return;
     try {
       final codec = await ui.instantiateImageCodec(await File(path).readAsBytes());

apps/desktop/lib/src/shell/session_player.dart

@@ -15,6 +15,7 @@ import '../queue/queue_ui.dart';
 import '../playback/media_marks.dart' show SkipKind, SkipOffer, formatClock;
 import '../screens/session/jellyfin_widgets.dart';
 import '../screens/session/player_controls.dart';
+import '../session/app_events.dart' show ShaderMessage;
 import '../session/session_coordinator.dart';
 import '../shaders/shader_presets.dart';
 import '../state/session_state.dart';
@@ -92,8 +93,6 @@ class _SessionPlayerState extends State<SessionPlayer> {
   final _noFocus = FocusNode(skipTraversal: true, canRequestFocus: false);
   DateTime? _lastKeyAt;
   late final void Function() _stopShaderWatch;
-  // Own toast ids, negative: the coordinator counts up from 1.
-  int _toastSeq = 0;
   int _shaderNoticeSeen = 0;
   bool _miniHover = false;
   // Whether the controls are up (their frame reports it).
@@ -134,7 +133,7 @@ class _SessionPlayerState extends State<SessionPlayer> {
       final n = _coord.playback.shaderNotice.value;
       if (n == null || n.id == _shaderNoticeSeen) return;
       _shaderNoticeSeen = n.id;
-      _toast(n.text);
+      _coord.notify(ShaderMessage(n.text));
     });
     _stopPopoverWatch = effect(() {
       _hold.set(#upNextPopover, _coord.queue.popoverOpen.value);
@@ -162,13 +161,6 @@ class _SessionPlayerState extends State<SessionPlayer> {
     super.dispose();
   }
 
-  void _toast(String text) {
-    _coord.toasts.value = [
-      ..._coord.toasts.peek(),
-      ToastItem(id: --_toastSeq, text: text, at: DateTime.now().toUtc()),
-    ];
-  }
-
   void _toggleChat() => _model.toggleChat();
 
   /// The player keys, while the player fills the body and nothing (a

apps/desktop/lib/src/shell/settings_tab.dart

@@ -2,9 +2,7 @@ import 'dart:async';
 
 import 'dart:io';
 
-import 'package:file_picker/file_picker.dart';
 import 'package:flutter/material.dart';
-import 'package:fox_utils/fox_utils.dart' show DesktopDropX, DropTarget;
 import 'package:signals/signals_flutter.dart';
 import 'package:sync_relay_core/core.dart'
     show CookieBrowser, CookieFile, NetscapeCookie, YtDlp, YtDlpCookies, cookieBrowsers, parseCookies;
@@ -12,7 +10,6 @@ import 'package:sync_relay_core/core.dart'
 import '../controls/player_settings.dart';
 import '../jellyfin/accounts.dart';
 import '../jellyfin/accounts_panel.dart';
-import '../playback/yt_dlp_app.dart';
 import '../schedule/animeflow.dart';
 import '../screens/home/about_page.dart';
 import '../screens/home/settings_page.dart';
@@ -380,7 +377,7 @@ class RecentServersPanel extends StatelessWidget {
 /// The app's yt-dlp (web page links): its version, "Update now", and the
 /// last error.
 class YtDlpSettings extends StatefulWidget {
-  /// Defaults to [AppYtDlp.instance]'s.
+  /// Defaults to the app's ([Ports.links]).
   final Future<YtDlp>? ytDlp;
   const YtDlpSettings({super.key, this.ytDlp});
 
@@ -389,7 +386,7 @@ class YtDlpSettings extends StatefulWidget {
 }
 
 class _YtDlpSettingsState extends State<YtDlpSettings> {
-  late final Future<YtDlp> _y = widget.ytDlp ?? AppYtDlp.instance.ytDlp;
+  late final Future<YtDlp> _y = widget.ytDlp ?? SessionState.instance.ports.links.ytDlp;
 
   @override
   Widget build(BuildContext context) {
@@ -472,18 +469,17 @@ class _YtDlpCookieSettingsState extends State<YtDlpCookieSettings> {
       };
 
   Future<void> _pickFile() async {
-    final List<PlatformFile> files;
+    final List<String> files;
     try {
-      files = await FilePicker.pickFiles(
+      files = await SessionState.instance.ports.folders.pickFiles(
         dialogTitle: 'Pick a cookies.txt or a JSON cookie export',
-        type: FileType.custom,
-        allowedExtensions: const ['txt', 'json'],
+        extensions: const ['txt', 'json'],
       );
     } catch (_) {
       _reload('file dialog unavailable — try again');
       return;
     }
-    final path = files.firstOrNull?.path;
+    final path = files.firstOrNull;
     if (path != null) await _importFile(path);
   }
 
@@ -535,12 +531,12 @@ class _YtDlpCookieSettingsState extends State<YtDlpCookieSettings> {
   @override
   Widget build(BuildContext context) {
     final scheme = Theme.of(context).colorScheme;
-    return DropTarget(
-      onDragEntered: (_) => setState(() => _dragging = true),
-      onDragExited: (_) => setState(() => _dragging = false),
-      onDragDone: (d) {
+    return SessionState.instance.ports.shell.dropTarget(
+      onEnter: () => setState(() => _dragging = true),
+      onExit: () => setState(() => _dragging = false),
+      onDrop: (paths, _) {
         setState(() => _dragging = false);
-        final path = DesktopDropX.pathsOf(d.files).firstOrNull;
+        final path = paths.firstOrNull;
         if (path != null) _importFile(path);
       },
       child: AnimatedContainer(