Restructure step 3: your server, Invite, version gate, AppGraph

- One server per app run (loopback, no password); Invite attaches an
  all-interfaces listener to the same server and Stop sharing detaches
  it (guests told with 4016); members, media and Up next never reset.
  No solo mode: you're home on your own server unless in a friend's.
- Navigation: none / yours / friend; a join passes a version gate on
  /health first (clear "they/you need to update", update offer).
- Invite as a value (host, port, name, password flag, version, fp
  reserved); addresses filtered (loopback, link-local, 198.18/15,
  bridges) and ranked; Sharing chip, Copy invite, Stop sharing.
- Alone looks like a plain player (alone replaces solo).
- AppGraph builds and disposes systems; widgets use AppScope;
  SessionState deleted; a test caps the remaining singletons.

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

apps/desktop/lib/src/controls/control_menus.dart

@@ -121,7 +121,7 @@ Future<void> runControlAction(BuildContext context, PlayerControlsModel model, C
       model.changeVideo();
     case ControlAction.copyLink:
       final link = model.link();
-      if (link != null) await copyToClipboard(link, done: 'Link copied');
+      if (link != null) await copyToClipboard(context, link, done: 'Link copied');
     case ControlAction.reload:
       model.reload();
     case ControlAction.markAllReady:

apps/desktop/lib/src/controls/model/controls_layout.dart

@@ -113,7 +113,7 @@ class ControlsSnapshot {
   final bool hasDuration;
 
   /// Watching alone (no one to mark ready).
-  final bool solo;
+  final bool alone;
 
   /// A link to copy (`SessionCoordinator.currentLink`).
   final bool hasLink;
@@ -126,7 +126,7 @@ class ControlsSnapshot {
     this.nextIsUpNext = false,
     this.hasChapters = false,
     this.hasDuration = false,
-    this.solo = false,
+    this.alone = false,
     this.hasLink = false,
     this.fullscreen = false,
     this.chatOpen = false,
@@ -167,7 +167,7 @@ List<ControlAction> menuActions(ControlsSnapshot s, Set<OptionalControl> hidden)
       ControlAction.skipForward => s.hasDuration,
       ControlAction.chat => hidden.contains(OptionalControl.chat),
       ControlAction.copyLink => s.hasLink,
-      ControlAction.markAllReady => !s.solo,
+      ControlAction.markAllReady => !s.alone,
       _ => true,
     })
       a,
@@ -208,7 +208,7 @@ String controlTooltip(BarControl c, ControlsSnapshot s) => switch (c) {
   BarControl.playPause => switch (s.play) {
     PlayState.playing => 'Pause for everyone (Space)',
     PlayState.waiting => 'Ready, waiting for the others (Space: not ready)',
-    PlayState.paused => s.solo ? 'Play (Space)' : 'Ready: play when everyone is (Space)',
+    PlayState.paused => s.alone ? 'Play (Space)' : 'Ready: play when everyone is (Space)',
     PlayState.finished => 'Ready (Space)',
   },
   BarControl.previous => 'Previous: ${s.previousLabel ?? ''}  (< or Shift+P)',

apps/desktop/lib/src/controls/model/controls_model.dart

@@ -7,7 +7,6 @@ import '../../playback/playback_controller.dart';
 import '../../queue/queue_controller.dart';
 import '../../session/session_coordinator.dart';
 import '../../shaders/shader_presets.dart';
-import '../../state/session_state.dart';
 import '../../state/settings.dart';
 import '../player_settings.dart' show applyShaderChoice;
 import '../volume.dart' as vol;
@@ -91,7 +90,7 @@ class PlayerControlsModel {
       nextIsUpNext: items.isNotEmpty,
       hasChapters: chapters.value.isNotEmpty,
       hasDuration: duration.value > Duration.zero,
-      solo: SessionState.instance.solo.value,
+      alone: coord.alone.value,
       // Not a signal: read again whenever the state changes.
       hasLink: coord.serverState.value != null && coord.currentLink() != null,
       fullscreen: fullscreen.value,
@@ -184,7 +183,7 @@ class PlayerControlsModel {
 
   /// Saved as the choice and applied live; a null quality keeps the
   /// saved one.
-  void pickShader(ShaderPreset preset, ShaderQuality? quality) => applyShaderChoice(preset, quality);
+  void pickShader(ShaderPreset preset, ShaderQuality? quality) => applyShaderChoice(coord, preset, quality);
 
   void toggleTimeDisplay() => settings.setTimeDisplay(settings.timeDisplay.peek().toggled);
 

apps/desktop/lib/src/controls/player_settings.dart

@@ -6,8 +6,9 @@ import 'package:sync_relay_core/core.dart' show JellyfinStreamType;
 
 import '../jellyfin/track_prefs.dart' show MpvTrack;
 import '../playback/playback_controller.dart' show PlaybackController, RenderMode;
+import '../session/session_coordinator.dart' show SessionCoordinator;
 import '../shaders/shader_presets.dart';
-import '../state/session_state.dart';
+import '../app/app_graph.dart';
 import '../shell/mark_problem.dart';
 import '../shell/motion.dart';
 import '../state/settings.dart';
@@ -200,11 +201,10 @@ class ProgressLineSetting extends StatelessWidget {
 
 /// Saves a shader choice (also used on the next join) and puts it on the
 /// running player, if any; the player announces the result.
-void applyShaderChoice(ShaderPreset preset, ShaderQuality? quality) {
+void applyShaderChoice(SessionCoordinator coord, ShaderPreset preset, ShaderQuality? quality) {
   final s = AppSettings.instance;
   if (quality != null) s.setShaderQuality(quality);
   s.setShaderPreset(preset);
-  final coord = SessionState.instance.coordinator;
   coord.markInput();
   coord.playback.applyShaders(announce: true);
 }
@@ -242,7 +242,7 @@ class ShaderPresetSetting extends StatelessWidget {
                 for (final p in ShaderPreset.values)
                   if (p != ShaderPreset.custom || hasCustom || preset == p) (p, p.label),
               ],
-              onChanged: (p) => applyShaderChoice(p, null),
+              onChanged: (p) => applyShaderChoice(AppScope.of(context).coordinator, p, null),
             ),
             if (preset.isAnime4k) ...[
               const SizedBox(width: 8),
@@ -250,7 +250,7 @@ class ShaderPresetSetting extends StatelessWidget {
                 key: const ValueKey('shader-quality'),
                 value: quality,
                 items: [for (final q in ShaderQuality.values) (q, q.label)],
-                onChanged: (q) => applyShaderChoice(preset, q),
+                onChanged: (q) => applyShaderChoice(AppScope.of(context).coordinator, preset, q),
               ),
             ],
           ],
@@ -265,9 +265,8 @@ class ShaderPresetSetting extends StatelessWidget {
 
 /// Puts the hwdec setting on the running player (mpv switches decoders
 /// on the fly). `SYNC_RELAY_HWDEC` wins, as at player start.
-Future<void> applyHwdecLive() async {
+Future<void> applyHwdecLive(PlaybackController playback) async {
   if ((Platform.environment['SYNC_RELAY_HWDEC'] ?? '').isNotEmpty) return;
-  final playback = SessionState.instance.coordinator.playback;
   if (!playback.alive.peek()) return;
   try {
     final dynamic platform = playback.player.platform;
@@ -308,7 +307,7 @@ class _HwdecSettingState extends State<HwdecSetting> {
           items: const [(HwdecMode.auto, 'Auto'), (HwdecMode.off, 'Off'), (HwdecMode.custom, 'Custom')],
           onChanged: (m) {
             _s.setHwdecMode(m);
-            applyHwdecLive();
+            applyHwdecLive(AppScope.of(context).coordinator.playback);
           },
         ),
         below: mode != HwdecMode.custom
@@ -324,7 +323,7 @@ class _HwdecSettingState extends State<HwdecSetting> {
                     border: OutlineInputBorder(),
                   ),
                   onChanged: _s.setHwdecCustom,
-                  onSubmitted: (_) => applyHwdecLive(),
+                  onSubmitted: (_) => applyHwdecLive(AppScope.of(context).coordinator.playback),
                 ),
               ),
       );
@@ -342,7 +341,7 @@ class TrackSetting extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final coord = SessionState.instance.coordinator;
+    final coord = AppScope.of(context).coordinator;
     return SignalBuilder(builder: (context) {
       final list = [
         for (final t in coord.playback.tracks.value)