OverlayBuild
internal class OverlayBuild(val jarEntries: Map<File, List<String>>, val renameFor: RenameFor, val pinned: LanguageVersion?, val failed: MutableSet<File>)
What a shard build reads: the entries to widen, whether each jar's bytes get renamed, the metadata level for the rebuilt kotlin_module, and where to record a jar that would not open.