Protocol 10 presence gate, drop/paste anywhere, quick UI fixes

Ready gate: whoever is in the server while it is not playing counts (joining
while playing does not pause anyone); a swap counts everyone present and
keeps ready flags; the quorum rule is gone. Optional 'Unready when the
video changes'. No 'Skip 1:30' guess when the media has chapters.

Drag & drop and Ctrl+V anywhere (fox_utils): files, folders and links get a
small card asking how to open them. Files series start collapsed.

UI: Tab never moves focus and Space is always ready outside text fields;
chat focuses its field; unread badge on uosc and a chip in fullscreen;
people-only chat with an Activity toggle; skip pills show 5 s then with
the controls; volume up to 150%; own avatar same size as the party.

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

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

@@ -0,0 +1,197 @@
+import 'dart:io';
+
+import 'package:flutter/material.dart';
+
+import '../files/scanner.dart' show FileKind, kindOf;
+import '../files/ui/file_tiles.dart' show baseName;
+import 'library_tab.dart' show offlinePutUpHint;
+
+// Something handed to the app, by a drop or by Ctrl+V outside a text
+// field: what it is ([classifyHandoff], pure) and the small card that asks
+// how to open it ([HandoffCard]). The shell wires both.
+
+/// What was dropped or pasted.
+sealed class Handoff {
+  const Handoff();
+}
+
+/// Video files (by the Files page's extensions), in the order given.
+final class HandoffVideos extends Handoff {
+  final List<String> paths;
+  const HandoffVideos(this.paths);
+}
+
+final class HandoffFolder extends Handoff {
+  final String path;
+  const HandoffFolder(this.path);
+}
+
+/// An http(s) link.
+final class HandoffLink extends Handoff {
+  final String url;
+  const HandoffLink(this.url);
+}
+
+/// An image file. Nothing takes one yet; the shell ignores it.
+final class HandoffImage extends Handoff {
+  final String path;
+  const HandoffImage(this.path);
+}
+
+final class HandoffNothing extends Handoff {
+  const HandoffNothing();
+}
+
+const _imageExtensions = {'png', 'jpg', 'jpeg', 'webp', 'gif', 'bmp'};
+
+final _link = RegExp(r'^https?://\S+$', caseSensitive: false);
+final _windowsAbsolute = RegExp(r'^([A-Za-z]:[\\/]|\\\\)');
+
+bool _absolute(String p) => p.startsWith('/') || _windowsAbsolute.hasMatch(p);
+
+/// A `file://` URI as a path; anything else as is.
+String _pathOf(String p) {
+  if (!p.startsWith('file://')) return p;
+  try {
+    return Uri.parse(p).toFilePath();
+  } catch (_) {
+    return p;
+  }
+}
+
+/// Classifies dropped or pasted [paths] (files first) or, when there are
+/// none, pasted [text]: a link, or one absolute path (or `file://` URI) per
+/// line. Videos win over folders, folders over images; paths that do not
+/// exist ([typeOf], defaults to the file system) count for nothing.
+Handoff classifyHandoff({
+  List<String> paths = const [],
+  String? text,
+  FileSystemEntityType Function(String path)? typeOf,
+}) {
+  final type = typeOf ?? (p) => FileSystemEntity.typeSync(p);
+  var list = [for (final p in paths) if (p.trim().isNotEmpty) _pathOf(p.trim())];
+  if (list.isEmpty && text != null) {
+    final t = text.trim();
+    if (_link.hasMatch(t)) return HandoffLink(t);
+    final lines = [for (final l in t.split(RegExp(r'[\r\n]+'))) if (l.trim().isNotEmpty) _pathOf(l.trim())];
+    if (lines.isEmpty || !lines.every(_absolute)) return const HandoffNothing();
+    list = lines;
+  }
+  final types = {for (final p in list) p: type(p)};
+  bool file(String p) => types[p] == FileSystemEntityType.file;
+  final videos = [for (final p in list) if (file(p) && kindOf(p) == FileKind.video) p];
+  if (videos.isNotEmpty) return HandoffVideos(videos);
+  for (final p in list) {
+    if (types[p] == FileSystemEntityType.directory) return HandoffFolder(p);
+  }
+  for (final p in list) {
+    final dot = p.lastIndexOf('.');
+    if (file(p) && dot >= 0 && _imageExtensions.contains(p.substring(dot + 1).toLowerCase())) {
+      return HandoffImage(p);
+    }
+  }
+  return const HandoffNothing();
+}
+
+/// What the card's buttons ask the shell to do.
+enum HandoffAction {
+  /// Put the (first) video up for everyone.
+  putUp,
+  /// Offline: list the video in Files → Recent and open it there.
+  openInFiles,
+  /// Add the video's folder (or the folder) to Files and open it.
+  addFolder,
+  /// Open Library → Link with the URL filled.
+  openLink,
+}
+
+/// The card asking how to open a [Handoff] (videos, a folder or a link);
+/// pops the [HandoffAction] chosen.
+class HandoffCard extends StatelessWidget {
+  final Handoff item;
+  final bool online;
+  const HandoffCard({super.key, required this.item, required this.online});
+
+  @override
+  Widget build(BuildContext context) {
+    final scheme = Theme.of(context).colorScheme;
+    void pick(HandoffAction a) => Navigator.of(context).pop(a);
+    Widget button(HandoffAction a, IconData icon, String label, {bool primary = false}) => primary
+        ? FilledButton.icon(
+            key: ValueKey('handoff-${a.name}'), onPressed: () => pick(a), icon: Icon(icon, size: 18), label: Text(label))
+        : OutlinedButton.icon(
+            key: ValueKey('handoff-${a.name}'), onPressed: () => pick(a), icon: Icon(icon, size: 18), label: Text(label));
+
+    final (IconData icon, String title, String detail, List<Widget> buttons) = switch (item) {
+      HandoffVideos(:final paths) => (
+          Icons.movie_outlined,
+          baseName(paths.first),
+          paths.length > 1 ? 'and ${paths.length - 1} more · the first one goes up' : 'A video on this computer',
+          [
+            if (online)
+              button(HandoffAction.putUp, Icons.play_arrow, 'Put it up', primary: true)
+            else
+              button(HandoffAction.openInFiles, Icons.history, 'Open in Files', primary: true),
+            button(HandoffAction.addFolder, Icons.create_new_folder_outlined, 'Add its folder to Files'),
+          ],
+        ),
+      HandoffFolder(:final path) => (
+          Icons.folder_outlined,
+          baseName(path),
+          path,
+          [button(HandoffAction.addFolder, Icons.create_new_folder_outlined, 'Add to Files', primary: true)],
+        ),
+      HandoffLink(:final url) => (
+          Icons.link,
+          url,
+          online ? 'Pick how the others get it on the Link page' : offlinePutUpHint,
+          [
+            button(HandoffAction.openLink, Icons.link, online ? 'Put it up as a link…' : 'Open in Link',
+                primary: true),
+          ],
+        ),
+      HandoffImage() || HandoffNothing() => (Icons.help_outline, '', '', const <Widget>[]),
+    };
+    return Material(
+      key: const ValueKey('handoff-card'),
+      elevation: 12,
+      color: scheme.surfaceContainer,
+      borderRadius: BorderRadius.circular(18),
+      child: ConstrainedBox(
+        constraints: const BoxConstraints(maxWidth: 380),
+        child: Padding(
+          padding: const EdgeInsets.fromLTRB(18, 16, 18, 16),
+          child: Column(
+            mainAxisSize: MainAxisSize.min,
+            crossAxisAlignment: CrossAxisAlignment.start,
+            children: [
+              Row(
+                children: [
+                  Icon(icon, color: scheme.primary),
+                  const SizedBox(width: 10),
+                  Expanded(
+                    child: Column(
+                      crossAxisAlignment: CrossAxisAlignment.start,
+                      children: [
+                        Text(title,
+                            maxLines: 2,
+                            overflow: TextOverflow.ellipsis,
+                            style: Theme.of(context).textTheme.titleSmall),
+                        Text(detail,
+                            maxLines: 2,
+                            overflow: TextOverflow.ellipsis,
+                            style: TextStyle(color: scheme.onSurfaceVariant, fontSize: 12)),
+                      ],
+                    ),
+                  ),
+                ],
+              ),
+              const SizedBox(height: 14),
+              Wrap(spacing: 8, runSpacing: 8, children: buttons),
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+}