The create endpoint shared the scanner's upsert (ON CONFLICT
(library_id, file_path) DO UPDATE SET updated_at = NOW() RETURNING *) —
so a POST naming an already-registered file returned 201 CREATED with
the OLD row while silently discarding everything the caller submitted.
Nothing depended on that lie: the app only GETs/PUTs media items, the
web only searches/purges/deletes, KOReader never calls it — the
endpoint's create path had zero production callers.
Split the API path from the scanner's idempotent upsert, which is kept
verbatim in CreateMediaItem (re-scan dedup remains its safety net):
- CreateMediaItemIfNew: same insert with ON CONFLICT DO NOTHING — the
loser of a create race writes nothing and returns no row.
- GetMediaItemByLibraryAndPath: fetch the existing row for the
duplicate response.
- Handler branch: on pgx.ErrNoRows → 200 OK with
{"duplicate": true, "message": ..., "item": <existing row>} instead
of a 201 pretending it created something. Real creates still answer
201 with the item as before.
Bulk-import shape (the reason for 200+flag over 409): a re-run after a
mid-import failure is harmless and countable — each response tells the
caller exactly which of the two things happened.
Verified by the full integration suite: 217 groups pass, zero failures,
including a new pin of the duplicate contract (same file_path twice in
one library → 201 then 200/duplicate:true, second payload not
overwritten).
John O'Keefe
da13898046