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。

src/core/api_format/conversion/normalizer.py

@@ -160,21 +160,6 @@ class FormatNormalizer(ABC):
     def _extract_extra(self, payload: dict[str, Any], known_keys: set[str]) -> dict[str, Any]:
         return {k: v for k, v in payload.items() if k not in known_keys}
 
-    @staticmethod
-    def _reorder_request_keys(
-        payload: dict[str, Any],
-        prefix_keys: tuple[str, ...],
-    ) -> dict[str, Any]:
-        """将指定字段前置，其余保持原序，用于稳定请求体前缀以提升 prompt cache 命中率。"""
-        ordered: dict[str, Any] = {}
-        for key in prefix_keys:
-            if key in payload:
-                ordered[key] = payload[key]
-        for key, value in payload.items():
-            if key not in ordered:
-                ordered[key] = value
-        return ordered
-
     def _merge_dropped(self, target: dict[str, int], source: dict[str, int]) -> None:
         for k, v in source.items():
             target[k] = target.get(k, 0) + int(v)

src/core/api_format/conversion/normalizers/openai.py

@@ -453,7 +453,7 @@ class OpenAINormalizer(FormatNormalizer):
                 if key in _CHAT_PASSTHROUGH_KEYS and key not in result and key not in _HANDLED_KEYS:
                     result[key] = value
 
-        return self._reorder_request_prefix_keys(result)
+        return result
 
     # =========================
     # Responses
@@ -1401,11 +1401,6 @@ class OpenAINormalizer(FormatNormalizer):
         joined = "\n\n".join(parts)
         return joined or None
 
-    _REQUEST_PREFIX_KEYS = ("model", "tools", "messages")
-
-    def _reorder_request_prefix_keys(self, payload: dict[str, Any]) -> dict[str, Any]:
-        return self._reorder_request_keys(payload, self._REQUEST_PREFIX_KEYS)
-
     def _openai_tools_to_internal(self, tools: Any) -> list[ToolDefinition] | None:
         if not tools or not isinstance(tools, list):
             return None

src/core/api_format/conversion/normalizers/openai_cli.py

@@ -76,8 +76,6 @@ from src.core.api_format.conversion.stream_events import (
 from src.core.api_format.conversion.stream_state import StreamState
 from src.core.logger import logger
 
-_OPENAI_CLI_REQUEST_PREFIX_KEYS = ("model", "instructions", "tools", "input")
-
 
 def _is_chat_completions_response(data: dict[str, Any]) -> bool:
     """检测数据是否为 OpenAI Chat Completions 格式（而非 Responses API 格式）。
@@ -103,18 +101,6 @@ def _get_openai_chat_normalizer() -> "FormatNormalizer | None":
     return format_conversion_registry.get_normalizer("openai:chat")
 
 
-def reorder_openai_cli_request_prefix_keys(payload: dict[str, Any]) -> dict[str, Any]:
-    """Keep the stable OpenAI Responses prefix ahead of the typically dynamic tail."""
-    ordered: dict[str, Any] = {}
-    for key in _OPENAI_CLI_REQUEST_PREFIX_KEYS:
-        if key in payload:
-            ordered[key] = payload[key]
-    for key, value in payload.items():
-        if key not in ordered:
-            ordered[key] = value
-    return ordered
-
-
 class OpenAICliNormalizer(FormatNormalizer):
     FORMAT_ID = "openai:cli"
     capabilities = FormatCapabilities(
@@ -282,7 +268,6 @@ class OpenAICliNormalizer(FormatNormalizer):
         result: dict[str, Any] = {"model": internal.model}
         if instructions_text or has_explicit_instructions:
             result["instructions"] = instructions_text or ""
-        # Keep the stable system prefix ahead of the typically dynamic input payload.
         result["input"] = self._internal_messages_to_input(
             internal.messages,
             system_to_developer=False,
@@ -409,7 +394,7 @@ class OpenAICliNormalizer(FormatNormalizer):
                 ):
                     result[key] = value
 
-        return self._reorder_request_prefix_keys(result)
+        return result
 
     # =========================
     # Responses
@@ -2135,9 +2120,6 @@ class OpenAICliNormalizer(FormatNormalizer):
         joined = "\n\n".join(parts)
         return joined or None
 
-    def _reorder_request_prefix_keys(self, payload: dict[str, Any]) -> dict[str, Any]:
-        return reorder_openai_cli_request_prefix_keys(payload)
-
     def _error_type_from_value(self, value: str) -> ErrorType:
         for t in ErrorType:
             if t.value == value: