Protocol 12: Up next (a shared queue) and where the video comes from

Up next: a server-side queue anyone edits by item id (add at end or
next, move, remove, play now, skip); each item says who added it and
how it plays. At the real end the first item swaps in after the end
card's countdown, put up by whoever can (its adder for through-me links
and files, someone with access for Jellyfin, else anyone); items that
can't play are skipped with the reason. The next item's link is
resolved ahead. Greyed "Continues with" episodes below. A chip with the
controls opens it as a popover (leaf_widgets, local path dependency for
now); "Add to queue" next to Put it up everywhere.

Delivery: the server measures the source's rate, the media's bitrate
and each member's read rate; the members card shows a source line
(who passes it on, through what, keeping up or not, source left) and
each member's route and buffer. A slow source is told once per media.
A failed server fetch is announced to everyone.

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

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

@@ -78,6 +78,8 @@ class LibraryTab extends StatefulWidget {
   final BrowseStart? jellyfinStart;
   /// Puts the pick up; returns an error text, or null when sent.
   final Future<String?> Function(PickedMedia media) onPutUp;
+  /// Adds a pick to Up next; null without a server (no queue actions).
+  final AddToQueue? onAddToQueue;
   final VoidCallback? onPutUpDone;
   final VoidCallback? onOpenIntegrations;
   /// Defaults to [RecentLinks.instance].
@@ -97,6 +99,7 @@ class LibraryTab extends StatefulWidget {
     required this.solo,
     required this.isHost,
     required this.onPutUp,
+    this.onAddToQueue,
     this.onPutUpDone,
     this.jellyfinStart,
     this.onOpenIntegrations,
@@ -164,6 +167,13 @@ class _LibraryTabState extends State<LibraryTab> {
 
   /// A Jellyfin card or episode: a series goes up as its next episode.
   Future<String?> _putUpJellyfin(JellyfinSelection sel) async {
+    final pick = await _jellyfinPick(sel);
+    return pick is JellyfinMedia ? _put(pick) : pick as String;
+  }
+
+  /// What a Jellyfin card stands for (a series: its next episode), or an
+  /// error text.
+  Future<Object> _jellyfinPick(JellyfinSelection sel) async {
     final account = widget.accounts.account(sel.serverId);
     final client = widget.accounts.clientFor(sel.serverId);
     if (account == null || client == null) return 'that Jellyfin server is not linked any more';
@@ -175,7 +185,23 @@ class _LibraryTabState extends State<LibraryTab> {
       return e.message;
     }
     if (item == null) return 'nothing to play in there';
-    return _put(pickFor(account, item));
+    return pickFor(account, item);
+  }
+
+  /// "Add to queue" on a Jellyfin card, episode or the details panel.
+  Future<String?> _queueJellyfin(JellyfinSelection sel, {bool next = false}) async {
+    final add = widget.onAddToQueue;
+    if (add == null) return null;
+    final pick = await _jellyfinPick(sel);
+    return pick is JellyfinMedia ? add(pick, next: next) : pick as String;
+  }
+
+  /// A card's menu: errors as a snack bar.
+  Future<void> _cardQueue(JellyfinSelection sel, {bool next = false}) async {
+    final error = await _queueJellyfin(sel, next: next);
+    if (error != null && mounted) {
+      ScaffoldMessenger.maybeOf(context)?.showSnackBar(SnackBar(content: Text(error)));
+    }
   }
 
   /// Double-click on a card: put it up, errors as a snack bar.
@@ -235,6 +261,7 @@ class _LibraryTabState extends State<LibraryTab> {
             selected: _c.selected,
             onSelect: _c.select,
             onPutUp: _doublePutUp,
+            onAddToQueue: widget.onAddToQueue == null ? null : _cardQueue,
             onOpenIntegrations: widget.onOpenIntegrations,
             start: widget.jellyfinStart,
             libraryStrip: false,
@@ -251,6 +278,7 @@ class _LibraryTabState extends State<LibraryTab> {
           recents: widget.recentLinks ?? RecentLinks.instance,
           probe: widget.probe,
           onPutUp: _put,
+          onAddToQueue: widget.onAddToQueue,
         ),
       MediaKind.file => _files(context),
     };
@@ -282,6 +310,7 @@ class _LibraryTabState extends State<LibraryTab> {
               selection: shown,
               solo: widget.solo,
               onPutUp: _putUpJellyfin,
+              onAddToQueue: widget.onAddToQueue == null ? null : _queueJellyfin,
               onClose: () => _c.select(null),
             ),
           ));
@@ -348,7 +377,13 @@ class _LibraryTabState extends State<LibraryTab> {
       if (b != null) {
         return b(context, solo: widget.solo, relayed: relayed, onPlay: play, nowPlayingPath: now);
       }
-      return FilesPage(solo: widget.solo, relayed: relayed, onPlay: play, nowPlayingPath: now);
+      final add = widget.onAddToQueue;
+      return FilesPage(
+          solo: widget.solo,
+          relayed: relayed,
+          onPlay: play,
+          onAddToQueue: add == null ? null : (path, {next = false}) => add(FileMedia(path), next: next),
+          nowPlayingPath: now);
     });
   }
 }