Package-level declarations

Live, mutable counterpart of a TileSchema instance in the rendered tree — one holder per tile, built by a TileHolderBuilder and owned by the screen's TilesManager for as long as that tile stays composed.

Contract every Tile — built-in or custom — implements to turn its own TileSchema subtype T into its matching live TileHolder subtype H. Registered against T's class via a TileDefinition, and invoked exclusively through BuilderScope.buildTileHolder (and, transitively, through List<TileSchema>?.buildTileHolders()) — nothing else in the framework constructs a TileHolder directly.