refactor(normalizer): 移除 request key reorder 机制，保持自然插入顺序

移除 OpenAI/OpenAI CLI normalizer 中的 _reorder_request_prefix_keys 及
基类 _reorder_request_keys 死代码，request_from_internal 直接返回构建
顺序的 dict，测试同步更新为验证自然插入顺序。

tests/core/api_format/conversion/test_cli_conversion.py

@@ -504,7 +504,7 @@ def test_openai_cli_custom_tool_and_choice_convert_to_openai_chat() -> None:
 
     out = reg.convert_request(openai_cli_req, "openai:cli", "openai:chat")
 
-    assert list(out.keys())[:3] == ["model", "tools", "messages"]
+    assert list(out.keys())[:3] == ["model", "messages", "tools"]
     assert out["tools"] == [
         {
             "type": "custom",
@@ -583,7 +583,7 @@ def test_openai_chat_web_search_options_convert_to_openai_cli_tools() -> None:
 
     out = reg.convert_request(openai_chat_req, "openai:chat", "openai:cli")
 
-    assert list(out.keys())[:3] == ["model", "tools", "input"]
+    assert list(out.keys())[:3] == ["model", "input", "tools"]
     assert out["tools"] == [
         {
             "type": "web_search",
@@ -760,6 +760,22 @@ def test_openai_cli_request_tool_choice_flat_function_roundtrip_preserved() -> N
     assert out["tool_choice"] == {"type": "function", "name": "read_file"}
 
 
+def test_openai_cli_request_from_internal_keeps_natural_insertion_order() -> None:
+    normalizer = OpenAICliNormalizer()
+    internal = normalizer.request_to_internal(
+        {
+            "model": "gpt-test",
+            "input": [],
+            "max_output_tokens": 32,
+            "tools": [{"type": "function", "name": "read_file"}],
+        }
+    )
+
+    out = normalizer.request_from_internal(internal)
+
+    assert list(out.keys())[:4] == ["model", "input", "max_output_tokens", "tools"]
+
+
 def test_claude_explicit_effort_preserved_in_openai_cli() -> None:
     reg = _make_registry_with_cli()
 

tests/core/api_format/conversion/test_openai_normalizer.py

@@ -237,6 +237,27 @@ def test_openai_request_preserves_empty_string_legacy_function_call_arguments()
     assert out["messages"][1]["tool_calls"][0]["function"]["arguments"] == ""
 
 
+def test_openai_request_from_internal_keeps_natural_insertion_order() -> None:
+    n = OpenAINormalizer()
+
+    req = {
+        "model": "gpt-4o-mini",
+        "messages": [{"role": "user", "content": "weather?"}],
+        "max_tokens": 12,
+        "tools": [
+            {
+                "type": "function",
+                "function": {"name": "get_weather", "parameters": {"type": "object"}},
+            }
+        ],
+    }
+
+    internal = n.request_to_internal(req)
+    out = n.request_from_internal(internal)
+
+    assert list(out.keys())[:4] == ["model", "messages", "max_tokens", "tools"]
+
+
 def test_openai_request_content_image_and_unknown_drop() -> None:
     n = OpenAINormalizer()