AEAT modelo 303 - OSS

This module extends the Spanish VAT self-assessment report (modelo 303) so that operations covered by the EU One-Stop Shop (OSS) appear in the correct boxes of the form.

• It adds new report boxes (fields 123, 124, 126 and 127) to the 2024 tax map used by the modelo 303: operations not subject to Spanish VAT because of localisation rules covered by OSS, and operations subject to and covered by OSS.
• For the OSS boxes, the tax search is widened: instead of the usual taxes, it picks up the company's taxes that have an OSS country set, so cross-border OSS sales are collected.
• Automatic rule: the summary boxes 126 and 127 are only filled in the last report of the year (4th quarter or December) and only when the company is not exonerated from filing modelo 390 and has operation volume. In any other period those boxes stay empty.
• When those summary boxes are computed, the date range is automatically widened to the whole year, so the annual OSS totals are correct.

It works on the modelo 303 report (l10n.es.aeat.mod303.report) and on the tax mapping lines (l10n.es.aeat.map.tax.line). No new menus or screens are added; the changes appear inside the existing modelo 303 report.