fix(dm): remove local append on send to prevent double messages

web/src/stores/conversation.ts

@@ -130,32 +130,29 @@ export const useConversationStore = create<ConversationState>((set, get) => ({
   },
 
   sendMessage: async (conversationId, content) => {
+    // don't append here — WS MESSAGE_CREATE broadcast is the single source of truth.
+    // Appending in both places caused double messages when the WS event arrived before the HTTP response.
     const message = await api.post<ConversationMessage>(
       `/conversations/${conversationId}/messages`,
       { content },
     );
-    set((state) => ({
-      messagesByConversation: {
-        ...state.messagesByConversation,
-        [conversationId]: [
-          ...(state.messagesByConversation[conversationId] || []),
-          message,
-        ],
-      },
-    }));
     return message;
   },
 
   addMessage: (message) => {
-    set((state) => ({
+    set((state) => {
+      const existing = state.messagesByConversation[message.conversation_id] || [];
+      if (existing.some((m) => m.id === message.id)) {
+        return state;
+      }
+      return {
         messagesByConversation: {
           ...state.messagesByConversation,
-        [message.conversation_id]: [
-          ...(state.messagesByConversation[message.conversation_id] || []),
-          message,
-        ].sort((a, b) => new Date(a.created_at).getTime() - new Date(b.created_at).getTime()),
+          [message.conversation_id]: [...existing, message]
+            .sort((a, b) => new Date(a.created_at).getTime() - new Date(b.created_at).getTime()),
         },
-    }));
+      };
+    });
   },
   updateMessage: (message) => {
     set((state) => {