prompt is now a string, not a tuple, copilot nailed this one

app.py

@@ -93,13 +93,13 @@ def on_submit(symptoms_text, history):
         md = getattr(node, 'metadata', {}) or {}
         context_list.append(f"{md.get('code','')}: {md.get('description','')}")
     context_text = "\n".join(context_list)
-    prompt = (
-        f"{SYSTEM_PROMPT}\n\n",
-        f"User symptoms: '{cleaned}'\n\n",
-        f"Relevant ICD-10 context:\n{context_text}\n\n",
-        "Respond with your top 3 ICD-10 codes and their confidence scores.\n\n",
-        "Think step by step and explain your reasoning.\n",
-    )
+    prompt = "\n".join([
+        f"{SYSTEM_PROMPT}",
+        f"User symptoms: '{cleaned}'",
+        f"Relevant ICD-10 context:\n{context_text}",
+        "Respond with your top 3 ICD-10 codes and their confidence scores.",
+        "Think step by step and explain your reasoning."
+    ])
 
     msg = "✏️ Prompt built"
     log.append(msg)