German GoBD 10-year digital invoice archive, how do you implement on Magento?

GoBD (Grundsätze zur ordnungsmäßigen Führung und Aufbewahrung von Büchern, Aufzeichnungen und Unterlagen in elektronischer Form) is the German tax-authority's digital bookkeeping standard. It mandates 10-year tamper-proof retention of every invoice, order confirmation, refund credit-note, and finance-related document, with full audit trail, immutability, and machine-readable search. For Magento we implement: (1) immutable PDF generation on every invoice/credit-memo save event, using mPDF or DomPDF rendered server-side, never client-cached; (2) SHA-256 checksum table per document, stored in a separate MySQL table that's append-only via DB trigger; (3) writes to an audit-log-protected S3 bucket (Hetzner Storage Box, AWS S3 Glacier, or Azure Blob immutable) with WORM (write-once-read-many) lifecycle policy; (4) a search index per Steuernummer + USt-IdNr + invoice date for Betriebsprüfung (tax audit) export; (5) ZUGFeRD/XRechnung hybrid PDFs satisfy GoBD + 2025+ B2B e-invoicing in one document. Auditor-ready from day 1.