Harden configuration validation

internal/config/config.go

@@ -83,6 +83,13 @@ type StorageConfig struct {
 	S3      *StorageS3Config `yaml:"s3"`
 }
 
+const (
+	// StorageBackendLocal disables remote object-store operations.
+	StorageBackendLocal = "local"
+	// StorageBackendS3 enables the configured S3 object store.
+	StorageBackendS3 = "s3"
+)
+
 // StorageS3Config configures S3 storage coordinates.
 type StorageS3Config struct {
 	Bucket         string `yaml:"bucket"`