🚧 Update topic explorer

backend/tests/conftest.py

@@ -256,6 +256,7 @@ def client(db_session, monkeypatch):
             self.id = id
             self.username = username
             self.topic_filter = topic_filter
+            self.buffer = []  # list of message dicts, index-tagged
 
     class FakeSessions:
         def __init__(self):
@@ -281,7 +282,8 @@ def client(db_session, monkeypatch):
     monkeypatch.setattr(explorer_module, "sessions", fake_sessions)
 
     def fake_messages_since(session_id, index):
-        return []
+        session = fake_sessions.get(session_id)
+        return [dict(m) for m in session.buffer if m["index"] > index]
 
     def fake_list_retained(max_results=200, timeout=3.0):
         return [