-- A story can have a single stitched audiobook — all its chapter
-- renders concatenated into one chaptered file (see the m4b built
-- from per-chapter narration_runs). audiobook_path is the path the
-- web server serves it from (e.g. /audio/The-Coast-Down.m4b); NULL
-- means no audiobook has been stitched yet.
ALTER TABLE stories
    ADD COLUMN IF NOT EXISTS audiobook_path text;