fix: 修复gpt->claude转换无法命中codex缓存问题

backend/internal/service/openai_gateway_messages.go

@@ -78,7 +78,12 @@ func (s *OpenAIGatewayService) ForwardAsAnthropic(
 		if err := json.Unmarshal(responsesBody, &reqBody); err != nil {
 			return nil, fmt.Errorf("unmarshal for codex transform: %w", err)
 		}
-		applyCodexOAuthTransform(reqBody, false, false)
+		codexResult := applyCodexOAuthTransform(reqBody, false, false)
+		if codexResult.PromptCacheKey != "" {
+			promptCacheKey = codexResult.PromptCacheKey
+		} else if promptCacheKey != "" {
+			reqBody["prompt_cache_key"] = promptCacheKey
+		}
 		// OAuth codex transform forces stream=true upstream, so always use
 		// the streaming response handler regardless of what the client asked.
 		isStream = true