elkay: undo lesson.py 506-521

phase/Student_view/lesson.py

@@ -504,13 +504,17 @@ def _render_lesson():
             st.button(label, key=f"jump_{i}", on_click=lambda j=i: st.session_state.update({"topic_idx": j}) or st.rerun())
 
 def _get_topics(level: str, module_id: int) -> List[Tuple[str, str]]:
+    """
+    Build the six-topic plan from metadata titles, try backend for each,
+    and if content is missing, provide a short fallback paragraph.
+    """
     cache_key = (level, module_id)
-    cached = st.session_state.topics_cache.get(cache_key)
-    if isinstance(cached, list) and len(cached) > 0:   # only trust non-empty cache
-        return cached
+    if cache_key in st.session_state.topics_cache:
+        return st.session_state.topics_cache[cache_key]
 
-    plan = _topic_plan(level, module_id)
+    plan = _topic_plan(level, module_id)   # six titles max
     out: List[Tuple[str, str]] = []
+
     for idx in range(len(plan)):
         title, content = _fetch_topic_from_backend(level, module_id, idx)
         if not content: