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>

packages/core/lib/src/constants.dart

@@ -1,5 +1,5 @@
 abstract class RelayConstants {
-  static const int protoVersion = 9;
+  static const int protoVersion = 10;
 
   // Relay (`/r/...`): a member's bytes through the server's buffer.
   static const int relaySliceBytes = 1 << 20;

packages/core/lib/src/sync_engine.dart

@@ -186,12 +186,17 @@ class SyncEngine {
     return left.clamp(0.0, full).toDouble();
   }
 
-  /// Any frame from a member: fresh again, and a ready member the stale
-  /// sweep took out of the set goes back in (ready && !inSet only arises
-  /// from that sweep).
+  /// Any frame from a member: fresh again. Back in the set: a ready member
+  /// the stale sweep (or a swap while it was stale) took out (ready &&
+  /// !inSet only arises from those), and any member back from stale while
+  /// not playing (like a join then).
   void _seen(EngineMember member) {
+    final wasStale = isStale(member);
     member.lastSeen = now;
-    if (member.ready && !member.inSet) member.inSet = true;
+    if (!member.inSet &&
+        (member.ready || (wasStale && transport != Transport.playing))) {
+      member.inSet = true;
+    }
   }
 
   /// Heartbeat: stale sweep, end of media.
@@ -202,8 +207,11 @@ class SyncEngine {
 
   String applyJoin(String token, String name, String avatar) {
     final id = 'm${_nextId++}';
+    // Joining while not playing: in the set, so the start waits for them;
+    // while playing, out until they ready (a late joiner never pauses).
     members[token] =
-        EngineMember(id: id, token: token, name: name, avatar: avatar, now: now);
+        EngineMember(id: id, token: token, name: name, avatar: avatar, now: now)
+          ..inSet = transport != Transport.playing;
     feed.add(FeedMessage(actor: name, action: 'join', at: now));
     return id;
   }
@@ -367,9 +375,11 @@ class SyncEngine {
     serverTime = now;
     eventId++;
     transport = Transport.held;
+    // Ready flags stay; everyone here now waits for everyone else here now
+    // (a stale member rejoins the set with its next frame if still ready).
+    final t = now;
     for (final member in members.values) {
-      member.ready = false;
-      member.inSet = false;
+      member.inSet = !isStale(member, t);
       member.buffered = 0;
     }
     feed.add(FeedMessage(actor: actor?.name ?? '?', action: 'swap', at: now));
@@ -448,12 +458,9 @@ class SyncEngine {
     }
     final inSet = members.values.where((m) => m.inSet).toList();
     if (inSet.isEmpty) return;
-    final freshCount =
-        members.values.where((m) => !isStale(m, t)).length;
-    final quorum = inSet.length >= 2 || freshCount <= 1;
     final allGood = inSet.every(
         (m) => m.ready && m.buffered >= need && !isStale(m, t));
-    if (allGood && quorum) {
+    if (allGood) {
       serverTime = t;
       eventId++;
       transport = Transport.playing;

packages/core/test/sync_engine_test.dart

@@ -37,12 +37,12 @@ void main() {
   });
 
   group('membership + gate', () {
-    test('join lands out-of-set, playback stays held', () {
+    test('join while held lands in the set, playback stays held', () {
       join('a', 'alice');
       expect(engine.transport, Transport.held);
-      expect(engine.members['a']!.inSet, isFalse);
+      expect(engine.members['a']!.inSet, isTrue);
       final state = engine.broadcast();
-      expect(state.members.single.inSet, isFalse);
+      expect(state.members.single.inSet, isTrue);
     });
 
     test('single ready + buffered auto-plays', () {
@@ -126,7 +126,22 @@ void main() {
     });
   });
 
-  group('quorum gate', () {
+  group('presence gate', () {
+    test('initial media: three join while held, two ready stays held', () {
+      engine.media = const HelloMedia(name: 'f', size: 1, duration: 0);
+      join('a', 'alice');
+      join('b', 'bob');
+      join('c', 'cara');
+      engine.applyReady('a', true);
+      engine.applyReady('b', true);
+      buffer('a', 6.0);
+      buffer('b', 6.0);
+      buffer('c', 6.0);
+      expect(engine.transport, Transport.held);
+      engine.applyReady('c', true);
+      expect(engine.transport, Transport.playing);
+    });
+
     test('one ready of two fresh stays held', () {
       join('a', 'alice');
       join('b', 'bob');
@@ -153,6 +168,7 @@ void main() {
       t = t.add(const Duration(seconds: 16));
       engine.applyReady('a', true);
       buffer('a', 6.0);
+      engine.tick();
       expect(engine.transport, Transport.playing);
     });
 
@@ -257,19 +273,66 @@ void main() {
     });
   });
 
-  group('swap resets everything', () {
-    test('swap bumps mediaId, clears sets, holds', () {
+  group('swap', () {
+    const ep2 = HelloMedia(name: 'Ep02.mkv', size: 9, duration: 90.0);
+
+    test('swap bumps mediaId, holds, keeps ready, fresh members in set', () {
       join('a', 'alice');
       engine.applyReady('a', true);
       buffer('a', 4.0);
       expect(engine.transport, Transport.playing);
-      engine.applySwap('a',
-          const HelloMedia(name: 'Ep02.mkv', size: 9, duration: 9.0));
+      engine.applySwap('a', ep2);
       expect(engine.mediaId, 2);
       expect(engine.transport, Transport.held);
       expect(engine.positionAt(), 0);
-      expect(engine.members['a']!.inSet, isFalse);
-      expect(engine.members['a']!.ready, isFalse);
+      expect(engine.members['a']!.inSet, isTrue);
+      expect(engine.members['a']!.ready, isTrue);
+      expect(engine.members['a']!.buffered, 0);
+      buffer('a', 4.0);
+      expect(engine.transport, Transport.playing);
+    });
+
+    test('a member present at the swap blocks until ready', () {
+      join('a', 'alice');
+      join('b', 'bob');
+      join('c', 'cara');
+      engine.applySwap('a', ep2);
+      engine.applyReady('a', true);
+      engine.applyReady('b', true);
+      buffer('a', 6.0);
+      buffer('b', 6.0);
+      buffer('c', 6.0);
+      expect(engine.transport, Transport.held);
+      expect(engine.members['c']!.inSet, isTrue);
+      engine.applyReady('c', true);
+      expect(engine.transport, Transport.playing);
+    });
+
+    test('a joiner while playing never holds anyone back', () {
+      join('a', 'alice');
+      engine.applySwap('a', ep2);
+      engine.applyReady('a', true);
+      buffer('a', 6.0);
+      expect(engine.transport, Transport.playing);
+      join('b', 'bob');
+      buffer('b', 0);
+      expect(engine.members['b']!.inSet, isFalse);
+      expect(engine.transport, Transport.playing);
+    });
+
+    test('a stale member stays out, rejoins with its next frame if ready', () {
+      join('a', 'alice');
+      join('b', 'bob');
+      engine.applyReady('b', true);
+      t = t.add(const Duration(seconds: 16));
+      engine.applyReady('a', true);
+      engine.applySwap('a', ep2);
+      expect(engine.members['b']!.inSet, isFalse);
+      buffer('a', 6.0);
+      expect(engine.transport, Transport.playing);
+      buffer('b', 0);
+      expect(engine.members['b']!.inSet, isTrue);
+      expect(engine.transport, Transport.held);
     });
   });
 
@@ -427,10 +490,13 @@ void main() {
           isTrue);
     });
 
-    test('unready member does not rejoin on reports', () {
+    test('unready late joiner does not join on reports', () {
       join('a', 'alice');
+      engine.applyReady('a', true);
       buffer('a', 6.0);
-      expect(engine.members['a']!.inSet, isFalse);
+      join('b', 'bob');
+      buffer('b', 6.0);
+      expect(engine.members['b']!.inSet, isFalse);
     });
   });