Python: clean up exception (#2319)

* Potential fix for code scanning alert no. 18: Information exposure through an exception

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

* Fix test

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Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

Author: moonbox3

python/packages/ag-ui/agent_framework_ag_ui/_endpoint.py

@@ -91,4 +91,4 @@ async def event_generator():
             )
         except Exception as e:
             logger.error(f"Error in agent endpoint: {e}", exc_info=True)
-            return {"error": str(e)}
+            return {"error": "An internal error has occurred."}

python/packages/ag-ui/tests/test_endpoint.py

@@ -154,7 +154,7 @@ async def test_endpoint_error_handling():
     assert response.status_code == 200
     content = json.loads(response.content)
     assert "error" in content
-    assert "Expecting value" in content["error"]
+    assert content["error"] == "An internal error has occurred."
 
 
 async def test_endpoint_multiple_paths():