-- The rewrite pass: an author re-authors existing chapter prose in
-- their own voice (canon preserved, prose reworked). body_md gets
-- overwritten with the rewritten version; body_md_original keeps
-- the pre-rewrite prose so the original is never lost. Populated
-- only on the FIRST rewrite of a chapter (if NULL) — subsequent
-- rewrites leave the original alone.
ALTER TABLE chapters
    ADD COLUMN IF NOT EXISTS body_md_original text;

-- Allow 'rewrite' as a generation_runs.kind.
ALTER TABLE generation_runs
    DROP CONSTRAINT generation_runs_kind_check;
ALTER TABLE generation_runs
    ADD CONSTRAINT generation_runs_kind_check
    CHECK (kind = ANY (ARRAY['gen', 'cleanup', 'audit', 'summary', 'embed', 'narrate_prep', 'rewrite']));