Server on an isolate, dedicated server binary, room -> server (proto 5)

- serve(Map config, events) is the one server entrypoint: the app
  hosts it via Isolate.spawn (crash surfaced on the Host card, logs
  forwarded as [server]); bin/server.dart is the dedicated server,
  compiled into the bundle as watch-together-server. --headless gone.
- Host identity via a per-hosting hostKey in hello, replacing the
  loopback heuristic.
- Rename room -> server across code, files and wire (t:"state",
  /health name); protocol bumped to 5.
- CI compiles the server binary; isolate smoke tests in server and
  desktop suites. Docs updated.

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

apps/desktop/lib/src/sync/state_diff.dart

@@ -19,9 +19,9 @@ class RateAction extends PlayerAction {
   const RateAction(this.rate);
 }
 
-double roomPositionAt(RoomBroadcast room, DateTime now) {
-  if (room.transport != 'playing') return room.position;
-  return room.position + now.difference(room.serverTime).inMilliseconds / 1000.0;
+double serverPositionAt(StateBroadcast state, DateTime now) {
+  if (state.transport != 'playing') return state.position;
+  return state.position + now.difference(state.serverTime).inMilliseconds / 1000.0;
 }
 
 bool seekLanded({required double ownPosition, required double target}) {
@@ -31,9 +31,9 @@ bool seekLanded({required double ownPosition, required double target}) {
   return true;
 }
 
-bool localPlayAllowed(RoomBroadcast room, String memberId) {
+bool localPlayAllowed(StateBroadcast state, String memberId) {
   if (memberId.isEmpty) return false;
-  for (final m in room.members) {
+  for (final m in state.members) {
     if (m.id == memberId) return m.inSet && m.ready;
   }
   return false;
@@ -45,7 +45,7 @@ bool localPlayAllowed(RoomBroadcast room, String memberId) {
 bool shouldReassertReady(MemberView? self) =>
     self != null && self.ready && !self.inSet && !self.stale;
 
-class RoomDiff {
+class StateDiff {
   static const debounceWindow = Duration(seconds: 2);
 
   int _lastEventId = -1;
@@ -57,14 +57,14 @@ class RoomDiff {
 
   bool get slowing => _slowing;
 
-  List<PlayerAction> diff(RoomBroadcast room, double ownPosition, DateTime now) {
+  List<PlayerAction> diff(StateBroadcast state, double ownPosition, DateTime now) {
     final out = <PlayerAction>[];
-    final roomPos = roomPositionAt(room, now);
+    final serverPos = serverPositionAt(state, now);
 
-    if (room.mediaId != _lastMediaId && _lastMediaId != -1) {
-      _lastEventId = room.eventId;
-      _lastTransport = room.transport;
-      _lastMediaId = room.mediaId;
+    if (state.mediaId != _lastMediaId && _lastMediaId != -1) {
+      _lastEventId = state.eventId;
+      _lastTransport = state.transport;
+      _lastMediaId = state.mediaId;
       _slowing = false;
       _deviatingSince = null;
       out.add(const SeekAction(0));
@@ -74,39 +74,39 @@ class RoomDiff {
     }
 
     if (_lastEventId == -1) {
-      _lastEventId = room.eventId;
-      _lastTransport = room.transport;
-      _lastMediaId = room.mediaId;
+      _lastEventId = state.eventId;
+      _lastTransport = state.transport;
+      _lastMediaId = state.mediaId;
       _deviatingSince = null;
-      out.add(SeekAction(roomPos));
-      out.add(TransportAction(room.transport == 'playing'));
+      out.add(SeekAction(serverPos));
+      out.add(TransportAction(state.transport == 'playing'));
       return out;
     }
 
-    if (room.eventId != _lastEventId) {
-      _lastEventId = room.eventId;
+    if (state.eventId != _lastEventId) {
+      _lastEventId = state.eventId;
       _slowing = false;
       _deviatingSince = null;
       out.add(const RateAction(1.0));
-      out.add(SeekAction(roomPos));
-      if (room.transport != _lastTransport) {
-        _lastTransport = room.transport;
-        out.add(TransportAction(room.transport == 'playing'));
+      out.add(SeekAction(serverPos));
+      if (state.transport != _lastTransport) {
+        _lastTransport = state.transport;
+        out.add(TransportAction(state.transport == 'playing'));
       }
       return out;
     }
 
-    if (room.transport != _lastTransport) {
-      _lastTransport = room.transport;
+    if (state.transport != _lastTransport) {
+      _lastTransport = state.transport;
       _slowing = false;
       _deviatingSince = null;
       out.add(const RateAction(1.0));
-      out.add(TransportAction(room.transport == 'playing'));
-      out.add(SeekAction(roomPos));
+      out.add(TransportAction(state.transport == 'playing'));
+      out.add(SeekAction(serverPos));
       return out;
     }
 
-    final drift = ownPosition - roomPos;
+    final drift = ownPosition - serverPos;
     if (_slowing) {
       if (drift.abs() < 0.1) {
         _slowing = false;
@@ -114,10 +114,10 @@ class RoomDiff {
       }
       return out;
     }
-    switch (correctionFor(ownPosition: ownPosition, roomPosition: roomPos)) {
+    switch (correctionFor(ownPosition: ownPosition, serverPosition: serverPos)) {
       case Correction.seek:
-        if (_deviatingEvent != room.eventId || _deviatingSince == null) {
-          _deviatingEvent = room.eventId;
+        if (_deviatingEvent != state.eventId || _deviatingSince == null) {
+          _deviatingEvent = state.eventId;
           _deviatingSince = now;
           break;
         }
@@ -125,7 +125,7 @@ class RoomDiff {
           break;
         }
         _deviatingSince = null;
-        out.add(SeekAction(roomPos));
+        out.add(SeekAction(serverPos));
       case Correction.slowDown:
         _deviatingSince = null;
         _slowing = true;

apps/desktop/lib/src/sync/sync_client.dart

@@ -9,13 +9,13 @@ enum SyncStatus { idle, connecting, open, kicked, closed, error }
 class SyncClient {
   WebSocketChannel? _channel;
   StreamSubscription? _sub;
-  final StreamController<RoomBroadcast> _rooms = StreamController.broadcast();
+  final StreamController<StateBroadcast> _states = StreamController.broadcast();
   final StreamController<FeedMessage> _feeds = StreamController.broadcast();
   final StreamController<String> _kicked = StreamController.broadcast();
   final StreamController<String> _errors = StreamController.broadcast();
   final StreamController<SyncStatus> _status = StreamController.broadcast();
 
-  Stream<RoomBroadcast> get rooms => _rooms.stream;
+  Stream<StateBroadcast> get states => _states.stream;
   Stream<FeedMessage> get feeds => _feeds.stream;
   Stream<String> get kicked => _kicked.stream;
   Stream<String> get errors => _errors.stream;
@@ -24,7 +24,7 @@ class SyncClient {
   String token = '';
   String memberId = '';
   String? mediaUrl;
-  RoomBroadcast? lastRoom;
+  StateBroadcast? lastState;
   Completer<WelcomeMessage>? _pendingWelcome;
 
   Future<WelcomeMessage> connect({
@@ -33,6 +33,7 @@ class SyncClient {
     required String name,
     String avatar = '',
     HelloMedia? media,
+    String hostKey = '',
   }) async {
     await disconnect();
     _status.add(SyncStatus.connecting);
@@ -61,6 +62,7 @@ class SyncClient {
       secret: secret,
       user: HelloUser(name: name, avatar: avatar),
       media: media ?? const HelloMedia(name: '', size: 0, duration: 0),
+      hostKey: hostKey,
     );
     ch.sink.add(jsonEncode(hello.toJson()));
     _pendingWelcome = welcomeCompleter;
@@ -74,8 +76,8 @@ class SyncClient {
       mediaUrl = welcome.mediaUrl;
       if (welcome.state != null) {
         try {
-          lastRoom = RoomBroadcast.fromJson(welcome.state!);
-          _rooms.add(lastRoom!);
+          lastState = StateBroadcast.fromJson(welcome.state!);
+          _states.add(lastState!);
         } catch (_) {}
       }
       _status.add(SyncStatus.open);
@@ -113,11 +115,11 @@ class SyncClient {
       return;
     }
     switch (t) {
-      case 'room':
+      case 'state':
         try {
-          final room = RoomBroadcast.fromJson(decoded);
-          lastRoom = room;
-          _rooms.add(room);
+          final state = StateBroadcast.fromJson(decoded);
+          lastState = state;
+          _states.add(state);
         } catch (_) {}
       case 'feed':
         try {
@@ -219,12 +221,12 @@ class SyncClient {
     token = '';
     memberId = '';
     mediaUrl = null;
-    lastRoom = null;
+    lastState = null;
   }
 
   Future<void> dispose() async {
     await disconnect();
-    await _rooms.close();
+    await _states.close();
     await _feeds.close();
     await _kicked.close();
     await _errors.close();