Keep null error fields from tripping replay failure

api/streaming.py

@@ -8106,7 +8106,7 @@ def _run_agent_streaming(
                 _drop_replayed_assistant = (
                     _agent_result_terminal_failure(result)
                     or bool(getattr(agent, '_last_error', None))
-                    or ('error' in result)
+                    or ('error' in result and result.get('error') is not None)
                 )
                 _saved_transcript_lacks_final_answer = _merged_transcript_lacks_final_assistant_answer(
                     _previous_messages,

tests/test_issue5121_provider_auth_terminal_error.py

@@ -377,6 +377,42 @@ def test_success_repeated_assistant_text_stays_successful_current_turn(tmp_path,
     assert not any(event == "apperror" for event, _ in events)
 
 
+def test_success_repeated_assistant_text_ignores_empty_error_field(tmp_path, monkeypatch):
+    session = _prepare_session("repeat_success_empty_error", "stream_repeat_success_empty_error", pending_user_message="Please say it again")
+    _seed_prior_turn(
+        session,
+        prior_user="Earlier question",
+        prior_assistant="Same answer",
+    )
+
+    class RepeatedSuccessWithEmptyErrorAgent(MockAgent):
+        def run_conversation(self, **kwargs):
+            history = list(kwargs.get("conversation_history") or [])
+            return {
+                "messages": history + [{"role": "assistant", "content": "Same answer"}],
+                "error": None,
+            }
+
+    fake_queue = _run_stream(
+        monkeypatch,
+        session,
+        "stream_repeat_success_empty_error",
+        RepeatedSuccessWithEmptyErrorAgent,
+        workspace=str(tmp_path),
+    )
+    saved = Session.load("repeat_success_empty_error")
+    assert saved is not None
+
+    assert any(msg.get("role") == "user" and msg.get("content") == "Please say it again" for msg in saved.messages)
+    assert saved.messages[-1]["role"] == "assistant"
+    assert saved.messages[-1]["content"] == "Same answer"
+    assert not any(msg.get("_error") for msg in saved.messages)
+
+    events = _queue_events(fake_queue)
+    assert any(event == "done" for event, _ in events)
+    assert not any(event == "apperror" for event, _ in events)
+
+
 def test_non_auth_silent_failure_still_uses_no_response(tmp_path, monkeypatch):
     session = _prepare_session("silent_failure", "stream_silent_failure", pending_user_message="Please handle silence")