feat(gateway): priority sorted based on config definition

llm-gateway/internal/provider/registry.go

@@ -19,6 +19,7 @@ type Route struct {
 // Registry maps model names to provider routes.
 type Registry struct {
 	routes map[string][]Route
+	order  []string // preserves config order
 }
 
 func NewRegistry(cfg *config.Config) (*Registry, error) {
@@ -28,8 +29,9 @@ func NewRegistry(cfg *config.Config) (*Registry, error) {
 		providers[pc.Name] = NewOpenAIProvider(pc.Name, pc.BaseURL, pc.APIKey, pc.Timeout)
 	}
 
-	// Build routes
+	// Build routes (preserving config order)
 	routes := make(map[string][]Route)
+	order := make([]string, 0, len(cfg.Models))
 	for _, mc := range cfg.Models {
 		var modelRoutes []Route
 		for _, rc := range mc.Routes {
@@ -52,9 +54,10 @@ func NewRegistry(cfg *config.Config) (*Registry, error) {
 			return modelRoutes[i].Priority < modelRoutes[j].Priority
 		})
 		routes[mc.Name] = modelRoutes
+		order = append(order, mc.Name)
 	}
 
-	return &Registry{routes: routes}, nil
+	return &Registry{routes: routes, order: order}, nil
 }
 
 // Lookup returns the routes for a model name.
@@ -63,12 +66,7 @@ func (r *Registry) Lookup(model string) ([]Route, bool) {
 	return routes, ok
 }
 
-// ModelNames returns all registered model names.
+// ModelNames returns all registered model names in config order.
 func (r *Registry) ModelNames() []string {
-	names := make([]string, 0, len(r.routes))
-	for name := range r.routes {
-		names = append(names, name)
-	}
-	sort.Strings(names)
-	return names
+	return r.order
 }