-- Attach every pre-existing bookmark to the owner reader, seeded between the
-- two migrate passes (Store.Open). The oldest reader is the owner by
-- construction: only the seed creates readers, and it runs once per database.
-- Run-once via the version table, like every migration.
UPDATE bookmarks SET reader_id = (SELECT id FROM readers ORDER BY id LIMIT 1);

-- Ownership lands structurally: reader_id becomes part of the key, so a
-- bookmark is one Reader's progress on one Series and a duplicate for the
-- same pair is impossible at the database level. Deleting a Reader takes
-- their bookmarks with them. The old text key is gone — the wire "key" is
-- derived as site:series_id on read, and nothing references the column.
-- Dropping it drops the primary key it carried; the composite key replaces
-- it, and the FK index the series constraint needs is created automatically.
ALTER TABLE bookmarks
  ALTER COLUMN reader_id SET NOT NULL,
  DROP COLUMN key,
  ADD PRIMARY KEY (reader_id, site, series_id),
  ADD CONSTRAINT bookmarks_reader_fk
    FOREIGN KEY (reader_id) REFERENCES readers (id) ON DELETE CASCADE;