fix(codex): align validation with normalization for empty stream output

The response validation stage unconditionally marked Codex Responses API
replies as invalid when response.output was empty, triggering unnecessary
retries and fallback chains. However, _normalize_codex_response can
recover from this state by synthesizing output from response.output_text.

Now the validation stage checks for output_text before marking the
response invalid, matching the normalization logic. Also fixes
logging.warning → logger.warning for consistency with the rest of the
file.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/run_agent/test_run_agent_codex_responses.py

@@ -386,6 +386,56 @@ def test_run_conversation_codex_plain_text(monkeypatch):
     assert result["messages"][-1]["content"] == "OK"
 
 
+def test_run_conversation_codex_empty_output_with_output_text(monkeypatch):
+    """Regression: empty response.output + valid output_text should succeed,
+    not trigger retry/fallback. The validation stage must defer to
+    _normalize_codex_response which synthesizes output from output_text."""
+    agent = _build_agent(monkeypatch)
+
+    def _empty_output_response(api_kwargs):
+        return SimpleNamespace(
+            output=[],
+            output_text="Hello from Codex",
+            usage=SimpleNamespace(input_tokens=5, output_tokens=3, total_tokens=8),
+            status="completed",
+            model="gpt-5-codex",
+        )
+
+    monkeypatch.setattr(agent, "_interruptible_api_call", _empty_output_response)
+
+    result = agent.run_conversation("Say hello")
+
+    assert result["completed"] is True
+    assert result["final_response"] == "Hello from Codex"
+
+
+def test_run_conversation_codex_empty_output_no_output_text_retries(monkeypatch):
+    """When both output and output_text are empty, validation should
+    correctly mark the response as invalid and trigger retry."""
+    agent = _build_agent(monkeypatch)
+    calls = {"api": 0}
+
+    def _fake_api_call(api_kwargs):
+        calls["api"] += 1
+        if calls["api"] == 1:
+            return SimpleNamespace(
+                output=[],
+                output_text=None,
+                usage=SimpleNamespace(input_tokens=5, output_tokens=3, total_tokens=8),
+                status="completed",
+                model="gpt-5-codex",
+            )
+        return _codex_message_response("Recovered")
+
+    monkeypatch.setattr(agent, "_interruptible_api_call", _fake_api_call)
+
+    result = agent.run_conversation("Say hello")
+
+    assert calls["api"] >= 2
+    assert result["completed"] is True
+    assert result["final_response"] == "Recovered"
+
+
 def test_run_conversation_codex_refreshes_after_401_and_retries(monkeypatch):
     agent = _build_agent(monkeypatch)
     calls = {"api": 0, "refresh": 0}