References from SII

This module extends the Chilean SII reference feature so that references are attached to invoices. On both customer and supplier invoice forms, a new "References" section appears where users can add one or more reference lines. Each line shows the document name, its SII code, the reference class, the motive and the date; the name and class are required.

The module also adds an Invoice field on the reference records themselves, so from a reference you can see which invoice it belongs to.

Automatic behaviour: - When an invoice is saved in draft, the system tries to build references automatically. For a credit note, it references the original invoice being refunded. For a normal invoice, it looks at the sales order lines behind the invoice and creates references from the related sales order, blanket order and outgoing delivery pickings that have a reference class. - Duplicate protection: the same document name and class cannot be added twice to the same invoice; a database rule blocks it and a check in code silently skips duplicates.

References are read-only once the invoice leaves draft, so they can only be edited while the invoice is still a draft. Deleting an invoice also deletes its references.