fix: print error

# What does this PR do?


## Test Plan

Author: ehhuang

src/llama_stack_client/lib/agents/agent.py

@@ -257,7 +257,15 @@ def create_turn(
             chunks = [x for x in self._create_turn_streaming(messages, session_id, toolgroups, documents)]
             if not chunks:
                 raise Exception("Turn did not complete")
-            return chunks[-1].event.payload.turn
+
+            last_chunk = chunks[-1]
+            try:
+                return last_chunk.event.payload.turn
+            except Exception as e:
+                if getattr(last_chunk, "error", None):
+                    raise RuntimeError(f"Turn did not complete. Error: {last_chunk.error}") from None
+                else:
+                    raise RuntimeError(f"Turn did not complete with output: {last_chunk}") from None
 
     def _create_turn_streaming(
         self,