fix(openai): do not normalize /completion API token based accounts

backend/internal/service/openai_gateway_chat_completions.go

@@ -46,7 +46,7 @@ func (s *OpenAIGatewayService) ForwardAsChatCompletions(
 	// 2. Resolve model mapping early so compat prompt_cache_key injection can
 	// derive a stable seed from the final upstream model family.
 	billingModel := resolveOpenAIForwardModel(account, originalModel, defaultMappedModel)
-	upstreamModel := normalizeCodexModel(billingModel)
+	upstreamModel := normalizeOpenAIModelForUpstream(account, billingModel)
 
 	promptCacheKey = strings.TrimSpace(promptCacheKey)
 	compatPromptCacheInjected := false

backend/internal/service/openai_gateway_messages.go

@@ -62,7 +62,7 @@ func (s *OpenAIGatewayService) ForwardAsAnthropic(
 
 	// 3. Model mapping
 	billingModel := resolveOpenAIForwardModel(account, normalizedModel, defaultMappedModel)
-	upstreamModel := normalizeCodexModel(billingModel)
+	upstreamModel := normalizeOpenAIModelForUpstream(account, billingModel)
 	responsesReq.Model = upstreamModel
 
 	logger.L().Debug("openai messages: model mapping applied",

backend/internal/service/openai_ws_forwarder.go

@@ -2515,7 +2515,7 @@ func (s *OpenAIGatewayService) ProxyResponsesWebSocketFromClient(
 			}
 			normalized = next
 		}
-		upstreamModel := normalizeCodexModel(account.GetMappedModel(originalModel))
+		upstreamModel := normalizeOpenAIModelForUpstream(account, account.GetMappedModel(originalModel))
 		if upstreamModel != originalModel {
 			next, setErr := applyPayloadMutation(normalized, "model", upstreamModel)
 			if setErr != nil {
@@ -2773,7 +2773,7 @@ func (s *OpenAIGatewayService) ProxyResponsesWebSocketFromClient(
 		mappedModel := ""
 		var mappedModelBytes []byte
 		if originalModel != "" {
-			mappedModel = normalizeCodexModel(account.GetMappedModel(originalModel))
+			mappedModel = normalizeOpenAIModelForUpstream(account, account.GetMappedModel(originalModel))
 			needModelReplace = mappedModel != "" && mappedModel != originalModel
 			if needModelReplace {
 				mappedModelBytes = []byte(mappedModel)