Add streaming LLM proposal support

tests/test_core_flow.py

@@ -253,9 +253,23 @@ class CoreFlowTests(unittest.TestCase):
             self.assertEqual(endpoint.provider, "codex")
             self.assertEqual(endpoint.base_url, "http://codex.example/v1")
             self.assertEqual(endpoint.wire_api, "responses")
+            self.assertFalse(endpoint.stream)
             self.assertEqual(endpoint.reasoning_effort, "high")
             self.assertEqual(endpoint.api_key_env, "OPENAI_API_KEY")
 
+    def test_endpoint_stream_flag(self) -> None:
+        endpoint = LLMEndpointSpec.from_dict(
+            {
+                "provider": "custom",
+                "base_url": "http://example/v1",
+                "wire_api": "chat.completions",
+                "stream": True,
+                "model": "x",
+                "api_key_env": "OPENAI_API_KEY",
+            }
+        )
+        self.assertTrue(endpoint.stream)
+
     def test_extract_response_text_supports_responses_api_output(self) -> None:
         text = _extract_response_text(
             {