Wire the multi-barcode store layer to HTTP and the operator console:
- adminhandler: add POST /products/{id}/barcodes, DELETE
/products/{id}/barcodes/{barcodeID}, and POST .../primary. A barcode
owned by another product returns 409 with the conflicting product
(gtin/product_id/product_name); an invalid GTIN returns 400.
- admin-frontend: BarcodesCard on the product detail page lists all
barcodes (primary starred), adds with type/pack-level/region, sets
primary, and deletes; audit labels for the new actions.
- public-frontend: product detail surfaces non-primary barcodes so a
case/region code resolves and is visible to consumers.
Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
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