Jellyfin end to end: per-viewer playback, progress, episodes, swap browser

- Host/swap send refs only; pasted Jellyfin links become refs; the host
  hands the relay its own app-obtained credential.
- Each viewer resolves with their own account (token in a header) or
  via the relay, else a clear blocked card with Link account.
- Per-account progress reporting (Playing/Progress/Stopped), 401 marks
  the account expired.
- Previous/next episode in the controls (< > / Shift+P/N), floating
  Next episode pill near the end, auto-advance countdown (one
  designated swapper), track carry-over per series.
- Swap panel uses the shared MediaPicker; browser location remembered
  per server and opens on the current series.
- Fix: states are applied one at a time (a stale pause could land
  after a newer play).

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

apps/desktop/lib/src/state/server_isolate.dart

@@ -131,6 +131,27 @@ class ServerIsolate {
     if (!_stopping) crash?.call(_lastError ?? 'the server stopped unexpectedly');
   }
 
+  /// Makes [path] the hosted file (the in-session File swap). Returns its
+  /// name and size for the `swap` that puts it up, or null when the file
+  /// is missing or the server is gone.
+  Future<({String name, int size})?> setFile(String path,
+      {Duration timeout = const Duration(seconds: 5)}) async {
+    if (_exited.isCompleted) return null;
+    final reply = ReceivePort('server file');
+    try {
+      _stop.send({'t': 'file', 'path': path, 'reply': reply.sendPort});
+      final msg = await reply.first.timeout(timeout);
+      if (msg is Map && msg['ok'] == true) {
+        return (name: msg['name'] as String, size: msg['size'] as int);
+      }
+      return null;
+    } catch (_) {
+      return null;
+    } finally {
+      reply.close();
+    }
+  }
+
   /// Asks the server to close its sockets and exit; kills the isolate if it
   /// has not exited within [timeout].
   Future<void> stop({Duration timeout = const Duration(seconds: 3)}) async {

apps/desktop/lib/src/state/session_state.dart

@@ -6,6 +6,8 @@ import 'package:flutter/widgets.dart';
 import 'package:signals/signals_flutter.dart';
 import 'package:sync_relay_core/core.dart';
 
+import '../jellyfin/accounts.dart';
+import '../jellyfin/session_media.dart';
 import '../sfx/sfx.dart';
 import '../session/health.dart';
 import '../session/session_coordinator.dart';
@@ -154,6 +156,7 @@ class SessionState {
   final SfxService sfx = const NoopSfxService();
   late final SessionCoordinator coordinator = SessionCoordinator(sfx: sfx);
   final lastForm = ConnectForm();
+  JellyfinAccounts get jellyfin => JellyfinAccounts.instance;
   /// Set when the hosted server died mid-session; Home shows it on the
   /// Host card and clears it.
   final serverCrash = signal<String?>(null);
@@ -232,6 +235,14 @@ class SessionState {
       if (op != _op) throw const ConnectCancelled();
       final hostKey = newHostKey();
       _setupCrash = null;
+      // A pasted Jellyfin link goes up as a ref like a browser pick.
+      final media = params.media ??
+          (params.linkUrl.isEmpty ? null : await mediaForLink(jellyfin, params.linkUrl));
+      if (op != _op) throw const ConnectCancelled();
+      // Guests without an account watch through the server, with the
+      // host's own sign-in (the hosted item's server, else the default).
+      await jellyfin.ensureLoaded(validate: false);
+      final relay = relayCredentialFor(jellyfin, serverId: media?.jellyfin?.serverId);
       late final ServerIsolate server;
       try {
         server = await ServerIsolate.start(
@@ -241,6 +252,7 @@ class SessionState {
             name: 'server',
             mediaPath: params.mediaPath,
             hostKey: hostKey,
+            jellyfin: relay,
           ),
           onLog: (line) => debugPrint('[server] $line'),
           onCrash: (cause) => _onServerCrash(server, cause),
@@ -256,6 +268,8 @@ class SessionState {
         throw const ConnectCancelled();
       }
       _server = server;
+      coordinator.hostFile = (path) async =>
+          identical(_server, server) ? server.setFile(path) : null;
       status.value =
           HealthStatus(HealthSeverity.ok, 'hosting on port ${server.port}');
       try {
@@ -265,8 +279,8 @@ class SessionState {
           secret: params.secret,
           name: params.name,
           avatar: params.avatar,
-          linkUrl: params.linkUrl,
           hostKey: hostKey,
+          media: media,
         ));
         if (op != _op) throw const ConnectCancelled();
       } catch (e) {
@@ -353,6 +367,7 @@ class SessionState {
   }
 
   Future<void> stopServer() async {
+    coordinator.hostFile = null;
     _stopKickWatch?.call();
     _stopKickWatch = null;
     final server = _server;

apps/desktop/lib/src/state/settings.dart

@@ -16,6 +16,7 @@ const _keyAutoCheckUpdates = 'autoCheckUpdates';
 const _keyShaderPreset = 'shaderPreset';
 const _keyShaderQuality = 'shaderQuality';
 const _keyCustomShaders = 'customShaders';
+const _keyAutoAdvance = 'autoAdvance';
 
 enum HwdecMode { auto, off, custom }
 
@@ -25,6 +26,8 @@ class AppSettings {
   final hwdecMode = signal(HwdecMode.auto);
   final hwdecCustom = signal('');
   final autoCheckUpdates = signal(true);
+  /// Jellyfin episodes: at the end, count down 10 s and put up the next.
+  final autoAdvance = signal(true);
 
   /// Video shaders: one choice, used on join and changed both here and
   /// in the session (Ctrl+0..6, the shader button).
@@ -59,6 +62,8 @@ class AppSettings {
       if (custom is String) hwdecCustom.value = custom;
       final auto = box.get(_keyAutoCheckUpdates);
       if (auto is bool) autoCheckUpdates.value = auto;
+      final advance = box.get(_keyAutoAdvance);
+      if (advance is bool) autoAdvance.value = advance;
       final preset = box.get(_keyShaderPreset);
       shaderPreset.value =
           ShaderPreset.values.where((p) => p.name == preset).firstOrNull ??
@@ -91,6 +96,11 @@ class AppSettings {
     _put(_keyAutoCheckUpdates, on);
   }
 
+  void setAutoAdvance(bool on) {
+    autoAdvance.value = on;
+    _put(_keyAutoAdvance, on);
+  }
+
   void setShaderPreset(ShaderPreset preset) {
     shaderPreset.value = preset;
     _put(_keyShaderPreset, preset.name);