fix(openai): keep xhigh normalization scoped to messages

backend/internal/service/openai_model_mapping.go

@@ -4,7 +4,6 @@ package service
 // forwarding. Group-level default mapping only applies when the account itself
 // did not match any explicit model_mapping rule.
 func resolveOpenAIForwardModel(account *Account, requestedModel, defaultMappedModel string) string {
-	requestedModel = NormalizeOpenAICompatRequestedModel(requestedModel)
 	if account == nil {
 		if defaultMappedModel != "" {
 			return defaultMappedModel

backend/internal/service/openai_model_mapping_test.go

@@ -58,19 +58,6 @@ func TestResolveOpenAIForwardModel(t *testing.T) {
 			defaultMappedModel: "gpt-4o-mini",
 			expectedModel:      "gpt-5.4",
 		},
-		{
-			name: "normalizes gpt reasoning alias before passthrough mapping",
-			account: &Account{
-				Credentials: map[string]any{
-					"model_mapping": map[string]any{
-						"gpt-5.4": "gpt-5.4",
-					},
-				},
-			},
-			requestedModel:     "gpt-5.4-xhigh",
-			defaultMappedModel: "gpt-5.1",
-			expectedModel:      "gpt-5.4",
-		},
 	}
 
 	for _, tt := range tests {