fix(agent-runner): stabilize event context and streams

tests/unit_tests/provider/requesters/test_chatcmpl_errors_direct.py

@@ -7,6 +7,7 @@ only the necessary dependencies.
 from __future__ import annotations
 
 import asyncio
+from types import SimpleNamespace
 from unittest.mock import AsyncMock, MagicMock
 import pytest
 import openai  # Import real openai package
@@ -140,6 +141,36 @@ class TestInvokeLLMErrorHandling:
 
         assert '频繁' in str(exc.value) or '余额' in str(exc.value)
 
+    @pytest.mark.asyncio
+    async def test_stream_skips_choice_with_none_delta(self, requester_with_mocked_client, mock_model):
+        """OpenAI-compatible streams may include choice frames with delta=None."""
+
+        async def fake_req_stream(args, extra_body=None):
+            yield SimpleNamespace(choices=[SimpleNamespace(delta=None, finish_reason=None)])
+            yield SimpleNamespace(
+                choices=[
+                    SimpleNamespace(
+                        delta=SimpleNamespace(model_dump=lambda: {'role': 'assistant', 'content': 'OK'}),
+                        finish_reason='stop',
+                    )
+                ]
+            )
+
+        requester_with_mocked_client._req_stream = fake_req_stream
+
+        chunks = [
+            chunk
+            async for chunk in requester_with_mocked_client._closure_stream(
+                query=None,
+                req_messages=[{'role': 'user', 'content': 'hello'}],
+                use_model=mock_model,
+            )
+        ]
+
+        assert len(chunks) == 1
+        assert chunks[0].content == 'OK'
+        assert chunks[0].is_final is True
+
 
 class TestInvokeEmbeddingErrorHandling:
     """Tests for invoke_embedding error handling."""