Update nodes.py

nodes.py

@@ -523,10 +523,15 @@ EXPLANATION:
         "review":      "Polished and explained"
     }
 
+
 # ─────────────────────────────────────────
 # NODE 13 — EXPLAINER (passthrough)
 # ─────────────────────────────────────────
 def explainer(state: State):
-    if not state.get("explanation"):
+    explanation = state.get("explanation")
+    if not explanation:
         return {"explanation": "Code completed successfully. See final code above."}
-    return {}
+    
+    # LangGraph requires a state update. 
+    # Re-writing the existing explanation satisfies this rule.
+    return {"explanation": explanation}