Part of #8 · Layer 3 (export) · 🟢 P1 · v1.2 / OG route

What

Initial @void-layer/export package with toSchemaOrgInvoice(invoice) → JSON-LD, wired into the opt-in OG public-layer route (<script type="application/ld+json">).

Why

• schema.org/PriceSpecification.priceCurrency explicitly accepts crypto tickers ("USDC") — spec-valid, no migration.
• Zero privacy cost (only the already-public OG layer), SEO + machine-readability gain.

Acceptance

• toSchemaOrgInvoice maps total/currency/payee/payer/dueDate/invoiceId
• emitted JSON-LD validates against schema.org Invoice
• wallet/chain/contract gaps expressed via additionalProperty (no blocker)
• only emitted on opt-in public layer — never on private fragment

wiki: concepts/schema-org-invoice.md, comparisons/currency-identifier-standards.md