feat: add connection status indicator with SSE heartbeat

- Add ConnectionIndicator component showing green/red dot
- Send lastPing signal every 15 seconds via SSE
- Indicator turns red if no ping received in 20 seconds
- Gives users confidence the live connection is active

chat/chat.go

@@ -76,11 +76,12 @@ func (r *Room) Send(msg Message) {
 	}
 }
 
-// receive processes an incoming NATS message, appending it to the buffer.
-func (r *Room) receive(data []byte) (Message, bool) {
+// Receive processes an incoming NATS message, appending it to the buffer.
+// Returns the new message and a snapshot of all messages.
+func (r *Room) Receive(data []byte) (Message, []Message) {
 	var msg Message
 	if err := json.Unmarshal(data, &msg); err != nil {
-		return msg, false
+		return msg, nil
 	}
 
 	r.mu.Lock()
@@ -88,9 +89,11 @@ func (r *Room) receive(data []byte) (Message, bool) {
 	if len(r.messages) > maxMessages {
 		r.messages = r.messages[len(r.messages)-maxMessages:]
 	}
+	snapshot := make([]Message, len(r.messages))
+	copy(snapshot, r.messages)
 	r.mu.Unlock()
 
-	return msg, true
+	return msg, snapshot
 }
 
 // Messages returns a snapshot of the current message buffer.
@@ -102,32 +105,15 @@ func (r *Room) Messages() []Message {
 	return snapshot
 }
 
-// Subscribe returns a channel of parsed messages and a cleanup function.
-// The room handles NATS subscription internally and buffers messages.
-func (r *Room) Subscribe() (<-chan Message, func()) {
-	natsCh := make(chan *nats.Msg, 64)
-	msgCh := make(chan Message, 64)
-
-	sub, err := r.nc.ChanSubscribe(r.subject, natsCh)
+// Subscribe creates a NATS channel subscription for the room's subject.
+// Caller is responsible for unsubscribing.
+func (r *Room) Subscribe() (chan *nats.Msg, *nats.Subscription, error) {
+	ch := make(chan *nats.Msg, 64)
+	sub, err := r.nc.ChanSubscribe(r.subject, ch)
 	if err != nil {
-		close(msgCh)
-		return msgCh, func() {}
+		return nil, nil, err
 	}
-
-	go func() {
-		for natsMsg := range natsCh {
-			if msg, ok := r.receive(natsMsg.Data); ok {
-				msgCh <- msg
-			}
-		}
-		close(msgCh)
-	}()
-
-	cleanup := func() {
-		_ = sub.Unsubscribe()
-	}
-
-	return msgCh, cleanup
+	return ch, sub, nil
 }
 
 func (r *Room) saveMessage(msg Message) {

features/c4game/handlers.go

@@ -142,8 +142,11 @@ func HandleGameEvents(store *connect4.Store, nc *nats.Conn, sm *scs.SessionManag
 		defer gameSub.Unsubscribe() //nolint:errcheck
 
 		// Subscribe to chat messages
-		chatCh, cleanupChat := room.Subscribe()
-		defer cleanupChat()
+		chatCh, chatSub, err := room.Subscribe()
+		if err != nil {
+			return
+		}
+		defer chatSub.Unsubscribe() //nolint:errcheck
 
 		ctx := r.Context()
 		for {
@@ -158,7 +161,8 @@ func HandleGameEvents(store *connect4.Store, nc *nats.Conn, sm *scs.SessionManag
 				if err := patchAll(); err != nil {
 					return
 				}
-			case chatMsg := <-chatCh:
+			case msg := <-chatCh:
+				chatMsg, _ := room.Receive(msg.Data)
 				err := sse.PatchElementTempl(
 					chatcomponents.ChatMessage(chatMsg, chatCfg),
 					datastar.WithSelectorID("c4-chat-history"),

features/snakegame/handlers.go

@@ -148,12 +148,15 @@ func HandleSnakeEvents(snakeStore *snake.SnakeStore, nc *nats.Conn, sm *scs.Sess
 		defer gameSub.Unsubscribe() //nolint:errcheck
 
 		// Chat subscription (multiplayer only)
-		var chatCh <-chan chat.Message
-		var cleanupChat func()
+		var chatCh chan *nats.Msg
+		var chatSub *nats.Subscription
 
 		if room != nil {
-			chatCh, cleanupChat = room.Subscribe()
-			defer cleanupChat()
+			chatCh, chatSub, err = room.Subscribe()
+			if err != nil {
+				return
+			}
+			defer chatSub.Unsubscribe() //nolint:errcheck
 		}
 
 		ctx := r.Context()
@@ -181,10 +184,11 @@ func HandleSnakeEvents(snakeStore *snake.SnakeStore, nc *nats.Conn, sm *scs.Sess
 					return
 				}
 
-			case chatMsg, ok := <-chatCh:
-				if !ok {
+			case msg := <-chatCh:
+				if msg == nil {
 					continue
 				}
+				chatMsg, _ := room.Receive(msg.Data)
 				err := sse.PatchElementTempl(
 					chatcomponents.ChatMessage(chatMsg, chatCfg),
 					datastar.WithSelectorID("snake-chat-history"),