fix(chat): NewStreamerHub accepts ConversationService interface; SSE handler drains ready events before ctx

internal/chat/streamer.go

@@ -107,23 +107,32 @@ type streamerHub struct {
 }
 
 // NewStreamerHub constructs a StreamerHub.
+// convSvc must be the concrete *conversationService produced by NewConversationService;
+// the type assertion lets callers in other packages pass the interface without needing
+// to import the unexported concrete type. Pass nil to skip title generation.
 func NewStreamerHub(
 	repo Repository,
 	registry clientGetter,
 	dispatch notifyDispatcher,
 	auditor audit.Recorder,
-	convSvc *conversationService,
+	convSvc ConversationService,
 	log *slog.Logger,
 	retention time.Duration,
 	safetyPct float64,
 ) StreamerHub {
+	var concrete *conversationService
+	if convSvc != nil {
+		if c, ok := convSvc.(*conversationService); ok {
+			concrete = c
+		}
+	}
 	return &streamerHub{
 		byMsgID:   make(map[int64]*streamer),
 		repo:      repo,
 		registry:  registry,
 		dispatch:  dispatch,
 		auditor:   auditor,
-		convSvc:   convSvc,
+		convSvc:   concrete,
 		log:       log,
 		retention: retention,
 		safety:    safetyPct,