[Epic]: V1→V2 parity — E-invoicing #666

Domain epic under the V1→V2 feature-parity umbrella (#136). Full audit: 04-einvoicing.md (2026-07-18 parity audit, v1 prep/v180 vs v2 develop).

Summary: Zero e-invoicing code exists in v2 (verified: no UBL/ZUGFeRD/Peppol/XML generation anywhere; MerchantClient is a payments record with no logic). Most of the v1 feature set is already tracked under #126's pluggable Peppol architecture — the real gaps are things #126 only mentions in passing (PDF embedding, readiness validation, offline delivery, inbound reception, two missing provider drivers) plus a deferred decision on Swiss Sumex/TARMED.

Sub-issues

• [Invoices]: Embed Factur-X/ZUGFeRD e-invoice XML into PDF/A-3 invoice PDFs #655 — Embed Factur-X/ZUGFeRD XML into PDF/A-3 invoice PDFs
• [Invoices]: E-invoicing readiness validation — required client and company fields #656 — E-invoicing readiness validation (required client/company fields)
• [Invoices]: E-invoice XML download action and email attachment (offline delivery) #657 — E-invoice XML download action and email attachment (offline delivery)
• [Invoices]: Inbound e-invoice reception — receive purchase documents from e-invoicing providers #658 — Inbound e-invoice reception
• [Invoices]: Qonto and SuperPdp e-invoicing provider drivers (v1.80 parity) #659 — Qonto and SuperPdp provider drivers
• [Invoices]: Sumex Swiss TARMED medical invoicing (decision needed) #660 — Sumex Swiss TARMED medical invoicing (decision needed)
• [Invoices]: Peppol e-invoicing — pluggable multi-provider architecture #126 — Peppol e-invoicing — pluggable multi-provider architecture (the parent architecture all of the above build on)
• [Invoices]: NLCIUS (Dutch CIUS) e-invoicing profile for UBL 2.1 export #487 — NLCIUS (Dutch CIUS) UBL 2.1 profile
• [Infrastructure]: Aruba electronic invoicing API integration (Italian FatturaPA) #379 — Aruba FatturaPA (Italy)
• [Core]: Certification with Portuguese TAX Authority (SAF-T) #407 — Portuguese SAF-T
• [Invoices]: Snapshot company contact data at invoice creation #382 — Company data snapshot (prerequisite for reproducible XML regeneration)

Specific

Reach e-invoicing feature parity with v1: working UBL/CII XML generation with country profiles, PDF/A-3 hybrid embedding, readiness validation, offline delivery, Peppol network transmission (outbound + inbound), and the full provider driver set v1.80 shipped.

Measurable

All 11 sub-issues closed; a company with e-invoicing enabled can generate valid, readiness-checked XML for its configured profile, deliver it via download/email/Peppol, and receive inbound documents.

Achievable

#126 is the architectural foundation (format handlers, provider registry) that #655/#657/#658/#659 build directly on top of; #487/#379/#407 are country-profile specializations of the same engine.

Relevant

E-invoicing is becoming legally mandatory in multiple EU markets (France B2B from 2026-09, Belgium Peppol from 2026-01); v2 currently has no path to compliance at all.

Time-Bound

#126's core handlers: several sprints (per its own Sprint 1-5 breakdown). Dependent issues here follow immediately after each relevant #126 milestone.