v9 created records with compression disabled at every level and fjall persists keyspace options on disk, so bodies written there stay uncompressed no matter what the schema says at open (measured on the prod db copy: 71.3MB stored vs 16MB zstd:3 standalone on the same bodies). the schema registers the store under a new name, heads, with zstd at every level, and v10 stages rewritten bodies straight into it, retiring both legacy stores in its finalize. chunked passes now resolve scan keyspaces through an on-disk fallback for stores the registry has dropped, pass the scanned keyspace to visit so in-place rewrites keep writing the store they read, and treat a never-existing source as a no-op when the pass is optional_on_absent. verified on a copy of the prod database: 136,311 entries migrated in ~500ms, heads compacts to 13.1MB (5.4x smaller), record resolution unchanged.