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/platform/app_log.dart

@@ -6,7 +6,7 @@ import 'package:sync_relay_core/core.dart';
 
 import '../screens/home/ui.dart' show appName, displayVersion;
 import 'ports/app_dirs.dart';
-import '../state/session_state.dart';
+import '../app/app_graph.dart';
 
 // The app's log on disk (<app support>/logs/app-YYYY-MM-DD.log; core's
 // logging.dart writes, rotates and redacts it), debugPrint routed into it,
@@ -50,19 +50,19 @@ Future<void> startAppLogging(AppDirs dirs) async {
 /// the app log (its hosted server's records included), already redacted;
 /// with [sessionLog], the server's session log of the same hours after it
 /// (every member's shared lines and the server's, merged).
-Future<String> diagnosticsText({Duration since = const Duration(hours: 6), bool sessionLog = false}) async {
+Future<String> diagnosticsText(AppGraph graph, {Duration since = const Duration(hours: 6), bool sessionLog = false}) async {
   final b = StringBuffer()
     ..writeln('$appName ${displayVersion()}')
     ..writeln('OS: ${Platform.operatingSystem} ${Platform.operatingSystemVersion}')
     ..writeln('Dart: ${Platform.version.split(' ').first}');
   try {
-    final mpv = await SessionState.instance.coordinator.playback.mpvVersion().timeout(const Duration(seconds: 2));
+    final mpv = await graph.coordinator.playback.mpvVersion().timeout(const Duration(seconds: 2));
     b.writeln('mpv: ${mpv ?? 'no player yet'}');
   } catch (_) {
     b.writeln('mpv: unknown');
   }
   try {
-    final y = await SessionState.instance.ports.links.ytDlp.timeout(const Duration(seconds: 2));
+    final y = await graph.ports.links.ytDlp.timeout(const Duration(seconds: 2));
     final cookies = y.cookies.read(count: false);
     b.writeln('yt-dlp: ${y.version ?? 'not ready'}${y.lastError == null ? '' : ' (${y.lastError})'}, '
         'cookies: ${cookies == null ? 'none' : 'set'}');
@@ -74,7 +74,7 @@ Future<String> diagnosticsText({Duration since = const Duration(hours: 6), bool
   b.writeln('--- last ${since.inHours} h of the log ---');
   b.write(files?.recent(since) ?? '');
   if (sessionLog) {
-    final server = await SessionState.instance.coordinator.sessionLog(hours: since.inHours);
+    final server = await graph.coordinator.sessionLog(hours: since.inHours);
     b
       ..writeln()
       ..writeln("--- last ${since.inHours} h of the server's session log ---")

apps/desktop/lib/src/platform/app_shutdown.dart

@@ -4,7 +4,7 @@ import 'dart:io';
 import 'package:flutter/foundation.dart';
 
 import '../files/thumbnails.dart';
-import '../state/session_state.dart';
+import '../app/app_graph.dart';
 
 // The one way out of the app (close button, Alt+F4, Update and restart).
 // Order matters: every mpv player goes before the engine does (a live one
@@ -18,33 +18,43 @@ bool _shuttingDown = false;
 /// True once [shutDownApp] started.
 bool get shuttingDown => _shuttingDown;
 
+/// The systems the close stops; `main` hands them over once.
+AppGraph? _graph;
+
+/// Makes [graph] the one [shutDownApp] stops and returns the close
+/// request handler for the window.
+Future<void> Function() closeAppWith(AppGraph graph) {
+  _graph = graph;
+  return shutDownApp;
+}
+
 /// Hides the window, releases every player and the sound device, leaves
-/// (the `bye` goes out first, so others see "left" at once; a hosted
+/// (the `bye` goes out first, so others see "left" at once; then your
 /// server stops), runs [beforeQuit], then closes the window. [restart]
 /// (Update and restart) leaves without the `bye`: the member stays
 /// `gone`, and the restarted app, same client id, takes it back within
 /// the grace. Every step is bounded; a second call does nothing.
 Future<void> shutDownApp({Future<void> Function()? beforeQuit, bool restart = false}) async {
-  if (_shuttingDown) return;
+  final graph = _graph;
+  if (_shuttingDown || graph == null) return;
   _shuttingDown = true;
-  final session = SessionState.instance;
-  final shell = session.ports.shell;
+  final shell = graph.ports.shell;
   final total = Stopwatch()..start();
   await _step('window save', shell.saveWindow(), const Duration(milliseconds: 500));
   await _step('hide', shell.hide(), const Duration(milliseconds: 500));
   await Future.wait([
-    _step('players', session.coordinator.releasePlayers(), const Duration(seconds: 3)),
+    _step('players', graph.coordinator.releasePlayers(), const Duration(seconds: 3)),
     _step('thumbnails', cancelAllThumbnails(), const Duration(milliseconds: 1500)),
-    _step('sounds', session.sfx.dispose(), const Duration(milliseconds: 500)),
+    _step('sounds', graph.sfx.dispose(), const Duration(milliseconds: 500)),
   ]);
   // Windows: media_kit_video frees a player's video output on a thread of
   // its own after dispose returns; it must be done before the engine
   // stops, or the plugin's teardown waits on it for good.
   if (Platform.isWindows) await Future.delayed(const Duration(milliseconds: 300));
-  // Jellyfin stop report, last diagnostics, the bye (flushed), then the
-  // hosted server: 3 s in all.
-  await _step('leave', session.leave(bye: !restart), const Duration(milliseconds: 2500));
-  await _step('server stop', session.stopServer(), const Duration(milliseconds: 500));
+  // Jellyfin stop report, last diagnostics, the bye (flushed), then your
+  // server: 3 s in all.
+  await _step('leave', graph.navigation.leave(bye: !restart), const Duration(milliseconds: 2500));
+  await _step('server stop', graph.yourServer.stop(), const Duration(milliseconds: 500));
   if (beforeQuit != null) await _step('before quit', beforeQuit(), const Duration(seconds: 3));
   debugPrint('close: ready to quit after ${total.elapsedMilliseconds} ms');
   await shell.quit();

apps/desktop/lib/src/platform/ports/ports.dart

@@ -12,7 +12,7 @@ export 'system_notifications.dart';
 export 'url_opener.dart';
 
 /// The platform as the app sees it: one set, made in the composition
-/// root ([SessionState]) and handed on from there.
+/// root ([AppGraph]) and handed on from there.
 class Ports {
   final ShellPort shell;
   final UrlOpener urls;