diff --git a/agent/chat_completion_helpers.py b/agent/chat_completion_helpers.py
index 5eca94a32..7a7064d72 100644
--- a/agent/chat_completion_helpers.py
+++ b/agent/chat_completion_helpers.py
@@ -2017,13 +2017,21 @@ def interruptible_streaming_api_call(agent, api_kwargs: dict, *, on_first_delta=
         request_client_holder["diag"] = _diag
         stream = request_client.chat.completions.create(**stream_kwargs)
 
-        # Some OpenAI-compatible adapters (for example copilot-acp) accept
-        # stream=True but still return a completed response object rather than
-        # an iterator of chunks.  Treat that as "streaming unsupported" for the
-        # rest of this session instead of crashing on ``for chunk in stream``
-        # with ``'types.SimpleNamespace' object is not iterable`` (#11732).
-        response_choices = getattr(stream, "choices", None)
-        if isinstance(response_choices, list) and response_choices:
+        # Some OpenAI-compatible adapters (for example copilot-acp, and the MoA
+        # openai-codex aggregator) accept stream=True but still return a
+        # completed response object rather than an iterator of chunks.  Treat
+        # that as "streaming unsupported" for the rest of this session instead
+        # of crashing on ``for chunk in stream`` with ``'types.SimpleNamespace'
+        # object is not iterable`` (#11732, #55933).
+        #
+        # Discriminate on the mere PRESENCE of a ``choices`` attribute, not on
+        # it being a non-empty list: an adapter may hand back a completed
+        # response whose ``choices`` is ``None`` or empty (an error /
+        # content-filter / terminal frame), and every such shape is still a
+        # whole response — not a token stream — that would crash iteration just
+        # the same.  A genuine provider stream (SDK ``Stream`` object,
+        # generator) exposes no ``choices`` attribute, so it is left untouched.
+        if hasattr(stream, "choices"):
             logger.info(
                 "Streaming request returned a final response object instead of "
                 "an iterator; switching %s/%s to non-streaming for this session.",
@@ -2031,7 +2039,13 @@ def interruptible_streaming_api_call(agent, api_kwargs: dict, *, on_first_delta=
                 agent.model or "unknown",
             )
             agent._disable_streaming = True
-            message = getattr(response_choices[0], "message", None)
+            # An empty/None ``choices`` carries no message to surface; return the
+            # completed object as-is so the outer loop's normal invalid-response
+            # validation (conversation_loop.py) handles it via the retry path,
+            # never ``for chunk in stream``.
+            choices = stream.choices
+            first_choice = choices[0] if isinstance(choices, (list, tuple)) and choices else None
+            message = getattr(first_choice, "message", None)
             if message is not None:
                 reasoning_text = (
                     getattr(message, "reasoning_content", None)
diff --git a/tests/run_agent/test_streaming.py b/tests/run_agent/test_streaming.py
index 2c4f8f8d0..7ccafff66 100644
--- a/tests/run_agent/test_streaming.py
+++ b/tests/run_agent/test_streaming.py
@@ -671,6 +671,53 @@ class TestStreamingFallback:
         assert agent._disable_streaming is True
         assert deltas == ["Hello from ACP"]
 
+    @pytest.mark.parametrize("choices", [[], None], ids=["empty", "none"])
+    @patch("run_agent.AIAgent._create_request_openai_client")
+    @patch("run_agent.AIAgent._close_request_openai_client")
+    def test_completed_response_no_usable_choices_returned_not_iterated(
+        self, mock_close, mock_create, choices
+    ):
+        """A completed response whose ``choices`` is empty ``[]`` or ``None`` is
+        still a whole (non-iterable) response, not a token stream.
+
+        The pre-existing guard (#55932) recognized a completed response only
+        when ``choices`` was a *non-empty* list, so an empty/terminal or
+        error/content-filter frame fell through to ``for chunk in stream`` and
+        crashed with ``'types.SimpleNamespace' object is not iterable`` (#55933,
+        hit by the MoA openai-codex aggregator). It must now disable streaming
+        and return the object for the outer loop's invalid-response retry path
+        instead of iterating it.
+        """
+        from run_agent import AIAgent
+
+        final_response = SimpleNamespace(model="gpt-5.5", choices=choices, usage=None)
+
+        mock_client = MagicMock()
+        mock_client.chat.completions.create.return_value = final_response
+        mock_create.return_value = mock_client
+
+        agent = AIAgent(
+            model="default",
+            provider="moa",
+            api_key="test-key",
+            base_url="moa://local",
+            quiet_mode=True,
+            skip_context_files=True,
+            skip_memory=True,
+        )
+        agent.api_mode = "chat_completions"
+        agent._interrupt_requested = False
+
+        deltas = []
+        agent._stream_callback = lambda text: deltas.append(text)
+
+        # Must NOT raise "'types.SimpleNamespace' object is not iterable".
+        response = agent._interruptible_streaming_api_call({})
+
+        assert response is final_response
+        assert agent._disable_streaming is True
+        assert deltas == []
+
     @patch("run_agent.AIAgent._create_request_openai_client")
     @patch("run_agent.AIAgent._close_request_openai_client")
     def test_stream_error_propagates_original(self, mock_close, mock_create):