fix: keep legacy subscription URLs working

backend/internal/router/subscription.go

@@ -13,8 +13,8 @@ import (
 	"gorm.io/gorm"
 )
 
-func RegisterPublicSubscriptionRoutes(api *gin.RouterGroup, db *gorm.DB, cfg *config.Config) {
-	handler := func(c *gin.Context) {
+func subscriptionHandler(db *gorm.DB, cfg *config.Config) gin.HandlerFunc {
+	return func(c *gin.Context) {
 		if db == nil {
 			c.JSON(http.StatusInternalServerError, gin.H{"error": "database is not configured"})
 			return
@@ -83,20 +83,22 @@ func RegisterPublicSubscriptionRoutes(api *gin.RouterGroup, db *gorm.DB, cfg *co
 		c.Header("Cache-Control", "no-store")
 		c.Data(http.StatusOK, "text/plain; charset=utf-8", converted)
 	}
+}
 
-	// Keep the current canonical API path and accept legacy subscription URLs
-	// so existing clients do not start returning 404 after an upgrade.
+func RegisterPublicSubscriptionRoutes(api *gin.RouterGroup, db *gorm.DB, cfg *config.Config) {
+	handler := subscriptionHandler(db, cfg)
 	api.GET("/client/sub/:token", handler)
 	api.GET("/client/sub/:token/", handler)
+}
 
-	// Legacy paths are registered on the engine root by SetupRouterWithDeps.
-	// The aliases below are attached to the same handler through the parent
-	// router group so all subscription URLs share exactly the same behavior.
-	root := api.Group("/")
-	root.GET("/sub/:token", handler)
-	root.GET("/sub/:token/", handler)
-	root.GET("/api/client/sub/:token", handler)
-	root.GET("/api/client/sub/:token/", handler)
+// RegisterLegacySubscriptionRoutes keeps subscription links generated by
+// older releases working after upgrading to the /api/v1 route layout.
+func RegisterLegacySubscriptionRoutes(r *gin.Engine, db *gorm.DB, cfg *config.Config) {
+	handler := subscriptionHandler(db, cfg)
+	r.GET("/sub/:token", handler)
+	r.GET("/sub/:token/", handler)
+	r.GET("/api/client/sub/:token", handler)
+	r.GET("/api/client/sub/:token/", handler)
 }
 
 func writeSubInfo(c *gin.Context, db *gorm.DB, tok string) {