diff --git a/packages/dashboard/src/__tests__/chat-manager.test.ts b/packages/dashboard/src/__tests__/chat-manager.test.ts
index 383d5c560..9d41b88a6 100644
--- a/packages/dashboard/src/__tests__/chat-manager.test.ts
+++ b/packages/dashboard/src/__tests__/chat-manager.test.ts
@@ -1838,6 +1838,7 @@ describe("ChatManager generation isolation", () => {
       role: "assistant",
       content: "",
     });
+    mockChatStore.getRoomMessages.mockReturnValue([]);
   });
 
   // Regression: a "Generation cancelled" broadcast from a previous generation