fix: 补全 OpenAI 工具参数 schema 中缺失的 properties 字段

OpenAI API 要求 type=object 的 schema 节点必须声明 properties，
否则会拒绝请求。在 request_from_internal 出口处对工具参数 schema
进行深拷贝并递归补全缺失的空 properties，不影响内部表示。

tests/core/api_format/conversion/test_cli_conversion.py

@@ -776,6 +776,21 @@ def test_openai_cli_request_from_internal_keeps_natural_insertion_order() -> Non
     assert list(out.keys())[:4] == ["model", "input", "max_output_tokens", "tools"]
 
 
+def test_openai_cli_request_from_internal_fixes_empty_object_tool_parameters() -> None:
+    normalizer = OpenAICliNormalizer()
+    internal = normalizer.request_to_internal(
+        {
+            "model": "gpt-test",
+            "input": [],
+            "tools": [{"type": "function", "name": "read_file", "parameters": {"type": "object"}}],
+        }
+    )
+
+    out = normalizer.request_from_internal(internal)
+
+    assert out["tools"][0]["parameters"] == {"type": "object", "properties": {}}
+
+
 def test_claude_explicit_effort_preserved_in_openai_cli() -> None:
     reg = _make_registry_with_cli()
 

tests/core/api_format/conversion/test_openai_normalizer.py

@@ -258,6 +258,26 @@ def test_openai_request_from_internal_keeps_natural_insertion_order() -> None:
     assert list(out.keys())[:4] == ["model", "messages", "max_tokens", "tools"]
 
 
+def test_openai_request_from_internal_fixes_empty_object_tool_parameters() -> None:
+    n = OpenAINormalizer()
+
+    req = {
+        "model": "gpt-4o-mini",
+        "messages": [{"role": "user", "content": "ping"}],
+        "tools": [
+            {
+                "type": "function",
+                "function": {"name": "noop", "parameters": {"type": "object"}},
+            }
+        ],
+    }
+
+    internal = n.request_to_internal(req)
+    out = n.request_from_internal(internal)
+
+    assert out["tools"][0]["function"]["parameters"] == {"type": "object", "properties": {}}
+
+
 def test_openai_request_content_image_and_unknown_drop() -> None:
     n = OpenAINormalizer()