Mapping Correction

arc-mapping creates a series that does not exist yet and stops there. Everything after that first insert lands here: extending, renumbering, and correcting rows that users are already reading.

REQUIRED BACKGROUND: arc-mapping defines the schema, the cumulative-episode convention, and the research sources. This skill assumes them.

Corrections are database writes. No commit, no release. Clients pick them up on next launch, which also means a bad write is live immediately.

Before writing anything

1. Read the current rows. Never edit blind.

   select s.id, s.title, s.anilist_anime_id, s.anilist_manga_id, s.source_notes,
          a.position, a.episode_start, a.episode_end, a.chapter_start, a.chapter_end, a.arc, a.season
   from series s join arc_mappings a on a.series_id = s.id
   where s.title ilike '%<show>%' order by a.position;
   

2. Re-fetch the counts. The AniList curl in arc-mapping step 1. Never carry forward a count from the original insert; that is what went stale.
3. Confirm the boundary against a source (fandom wiki, Wikipedia episode list, AniList forum guide) before changing a number. An audit finding is a prompt to research, not a fact.

The four corrections

Situation	What changes
Manga published further	Extend the last arc's chapter_end, or append a new arc with episode_start/episode_end NULL. Update source_notes with the new chapter count.
New season aired	Convert the affected tail arcs from NULL episodes to real cumulative ranges, and/or insert new arcs. Set season. Update source_notes arithmetic.
Boundary was wrong	Change chapter_start/chapter_end on both adjacent arcs so they stay contiguous. Fixing one side creates a gap or an overlap.
Film missing or misplaced	Insert into movies at the right position and renumber the rest. movies.length is what the series page displays.

Inserting into the middle

arc_mappings and movies both carry unique (series_id, position), so a naive insert collides. Shift the tail first, in one statement, descending:

-- make room at position 5
update arc_mappings set position = position + 1
where series_id = <id> and position >= 5;

insert into arc_mappings (series_id, position, episode_start, episode_end, chapter_start, chapter_end, arc, season)
values (<id>, 5, 137, 148, 302, 327, 'Culling Game Arc', 3);

Deleting an arc requires the mirror: delete, then position = position - 1 for everything after it. Positions must stay a dense 0-based run.

Always finish with

bun run scripts/audit-mappings.ts --series "<show>" --no-ignore

--no-ignore matters here: if the series has triaged entries, the default run hides exactly the codes you are most likely to have just broken.

Common mistakes

Mistake	Consequence
Treating new-season episodes as starting at 1	Episodes are cumulative across seasons. S3E1 of a 24-episode run is episode 25.
Changing anilist_anime_id to the new season's id	The first season's id is the stable key. Changing it orphans user progress and breaks existing links.
Fixing one side of a boundary	Leaves a gap or an overlap. Always edit both adjacent arcs.
Extending the last arc past the real chapter count	catalog-behind-manga becomes catalog-ahead-of-manga and the UI promises chapters that do not exist.
Leaving source_notes stale	It is the only record of the cumulative arithmetic and manga state. The next correction depends on it.
Inserting without shifting position	Violates unique (series_id, position); the write fails or, worse, you renumber by hand and skip one.