refactor: centralize llm provider transport

app/tests/test_preservation_slice_review_alerts.py

@@ -109,11 +109,12 @@ class ReviewAlertsSliceSourceEquivalenceTests(unittest.TestCase):
         for name in sorted(expected):
             self.assertEqual(migrated[name], original[name], name)
 
-    def test_review_assistant_agent_is_an_exact_file(self) -> None:
-        self.assertEqual(
-            sha256(ORIGINAL_ROOT / "assistant_agent.py"),
-            sha256(APP_ROOT / "backend" / "features" / "review" / "agent.py"),
-        )
+    def test_review_assistant_agent_uses_shared_transport(self) -> None:
+        source = (
+            APP_ROOT / "backend" / "features" / "review" / "agent.py"
+        ).read_text(encoding="utf-8")
+        self.assertIn("llm_transport.stream_chat_completion", source)
+        self.assertNotIn("urllib.request", source)
 
     def test_review_assistant_compatibility_module_is_canonical(self) -> None:
         self.assertIs(assistant_agent, canonical_agent)