-- chapter_sources: drop the global (source_id, source_chapter_key) PK
-- and rekey on (source_id, chapter_id).
--
-- The old PK assumed chapter slugs are unique per source. Sources whose
-- chapter naming is per-manga (chapter-1, chapter-2, ...) instead of per-
-- catalog (br_chapter-379272 with a global counter) would collide on the
-- second manga: the INSERT would conflict on (source_id, "chapter-1") and
-- the lookup would attribute the row to the first manga's chapter_id.
--
-- The new key is the natural identity of a source attachment: "this source
-- has this chapter". An (source_id, source_chapter_key) index preserves
-- the lookup path (find existing source row by source's identifier) but
-- no longer enforces uniqueness — the application combines it with the
-- chapters table's manga_id to scope the lookup per-manga.

ALTER TABLE chapter_sources DROP CONSTRAINT chapter_sources_pkey;
ALTER TABLE chapter_sources ADD PRIMARY KEY (source_id, chapter_id);

CREATE INDEX chapter_sources_source_key_idx
    ON chapter_sources (source_id, source_chapter_key);