ephemeral and links-only are a database identity choice, not a runtime toggle: a storage-mode marker written at adoption lets open reject a definite mismatch before migrations or compaction filters mutate anything. pre-marker databases are adopted after migration, when their record layout is inferable (markerless v9 inference). a migrated ephemeral database now rejects a permanent-mode open instead of silently changing shape. issue: hydrant-adq