fix(openai): handle codex spark model limitations

backend/internal/service/openai_model_mapping.go

@@ -1,5 +1,7 @@
 package service
 
+import "strings"
+
 // resolveOpenAIForwardModel determines the upstream model for OpenAI-compatible
 // forwarding. Group-level default mapping only applies when the account itself
 // did not match any explicit model_mapping rule.
@@ -12,8 +14,28 @@ func resolveOpenAIForwardModel(account *Account, requestedModel, defaultMappedMo
 	}
 
 	mappedModel, matched := account.ResolveMappedModel(requestedModel)
-	if !matched && defaultMappedModel != "" {
+	if !matched && defaultMappedModel != "" && !isExplicitCodexModel(requestedModel) {
 		return defaultMappedModel
 	}
 	return mappedModel
 }
+
+func isExplicitCodexModel(model string) bool {
+	model = strings.TrimSpace(model)
+	if model == "" {
+		return false
+	}
+	if strings.Contains(model, "/") {
+		parts := strings.Split(model, "/")
+		model = parts[len(parts)-1]
+	}
+	model = strings.ToLower(strings.TrimSpace(model))
+	if getNormalizedCodexModel(model) != "" {
+		return true
+	}
+	if strings.HasSuffix(model, "-openai-compact") {
+		base := strings.TrimSuffix(model, "-openai-compact")
+		return getNormalizedCodexModel(base) != ""
+	}
+	return false
+}