fix: accept endpoint-only parties in Flow 2 invoice inbox rules

[alvarolivie]

Why

Blocks the gobl.ubl / gobl.cii endpoint-mapping release. Those
converters are switching the party electronic address to GOBL's
org.Endpoint (iso6523-actorid-upis::<scheme>:<code>) instead of the
deprecated org.Inbox (invopop/gobl.ubl#111, invopop/gobl.cii#68). As a
result, a French B2B invoice parsed from UBL/CII now carries an
endpoint and no inbox — and fails Flow 2 validation, which requires an
inbox:

[GOBL-FR-CTC-FLOW2-BILL-INVOICE-11] ($.doc.supplier.inboxes) ... required (BR-FR-13)
[GOBL-FR-CTC-FLOW2-BILL-INVOICE-13] ($.doc.supplier) ... inbox with scheme 0225 ... (BR-FR-21/22)
[GOBL-FR-CTC-FLOW2-BILL-INVOICE-14] ($.doc.customer.inboxes) ... required (BR-FR-13)

What

normalizeParty now back-fills the Peppol inbox from the party's
endpoint when the party carries an iso6523-actorid-upis::<scheme>:<code>
endpoint but no inbox. This is the inverse of the eu/en16931 addon's
inbox→endpoint migration, so the existing BR-FR-13/21/22 rules are
satisfied without touching the rules themselves. Parties that already
carry an inbox are left untouched, and non-Peppol endpoints (e.g.
mailto:) are ignored.

After normalization a party ends up with both representations (inbox +
endpoint), matching how en16931-normalized documents already look — so
every consumer works regardless of which field it reads.

Scope

Flow 2 (invoice) only — the path the converters exercise. Flow 6 (CDAR
status) keeps its own inbox handling; the converters' CDAR path is
unchanged, so it isn't affected here.

Verification

• New unit tests: normalizeParty back-fills from a Peppol endpoint,
  skips when an inbox already exists, and ignores mailto: endpoints.
• New end-to-end test TestInvoiceB2BEndpointOnlyParties: a full French
  B2B invoice with endpoint-only parties now passes Calculate +
  Validate.
• Confirmed against gobl.ubl via a local replace: parsing the French
  b2b-reg.xml and validating no longer emits INVOICE-11/13/14 (only
  unrelated pre-existing sample-data errors remain).

Release

Cut a new tag after merge; gobl.ubl and gobl.cii bump to it in their
respective PRs before their own merge.

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

❌ Patch coverage is 80.00000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.80%. Comparing base (e1cfb0b) to head (9e1ab88).

Files with missing lines	Patch %	Lines
addon/flow2/org.go	80.00%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #14      +/-   ##
==========================================
- Coverage   96.96%   96.80%   -0.16%     
==========================================
  Files          13       13              
  Lines        2141     2161      +20     
==========================================
+ Hits         2076     2092      +16     
- Misses         44       46       +2     
- Partials       21       23       +2     

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[Copilot]

Pull request overview

This PR updates Flow 2 (invoice) party normalization so that parties expressed only with a Peppol participant endpoint (and no legacy inbox) still satisfy the existing Flow 2 inbox validation rules, unblocking endpoint-mapping changes in upstream UBL/CII converters.

Changes:

• Add Flow 2 party normalization logic to back-fill a Peppol inbox from an iso6523-actorid-upis::… endpoint when no inbox is present.
• Add unit tests covering inbox back-fill behavior (back-fill, no-op when inbox exists, ignore non-Peppol endpoints).
• Add an end-to-end Flow 2 invoice test ensuring endpoint-only supplier/customer parties pass Calculate + Validate.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
addon/flow2/org.go	Adds endpoint→inbox back-fill during party normalization for Flow 2 invoices.
addon/flow2/org_test.go	Adds unit tests for endpoint-only party normalization behavior.
addon/flow2/flow2_test.go	Adds an end-to-end invoice test for endpoint-only parties passing validation.

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