-- Real-world sources publish multiple chapters at the same number:
-- different uploaders, translator notices/farewells, paid-vs-free
-- re-uploads, and our own users can legitimately have two versions of
-- "Ch.52" with different scanlations. The (manga_id, number) UNIQUE
-- from 0001_init silently collapses all of those into a single row via
-- ON CONFLICT, dropping data. Drop the constraint and lean on the
-- chapter id (UUID) as the only chapter identity going forward.

ALTER TABLE chapters DROP CONSTRAINT chapters_manga_id_number_key;

-- The UNIQUE was also our only index on (manga_id, number) since
-- 0007 dropped the redundant explicit one. Chapter list pages
-- ORDER BY number ASC and the manga page is a hot read path, so put
-- the index back without the uniqueness. Secondary sort by created_at
-- so duplicate-numbered chapters have a stable order in lists and
-- prev/next navigation.
CREATE INDEX chapters_manga_id_number_idx
    ON chapters (manga_id, number, created_at);