Berichtenbox delivery waits on the Logius connection and answers to Q1 to Q9 #2605

What is missing

No Berichtenbox letter reaches a real citizen yet. The client follows the Logius interface, but every live proof ran against an XSD-validating fake.

Why it matters

dossiq and pipelinq send digital post through integriq. Until the connection is live, those letters stop at integriq.

Where

• Client: lib/Service/DigitalPost/ (BerichtenboxClientHttp, ebMS adapter, WUS ValidateAbonnementen).
• Open questions: openspec/changes/berichtenbox-client/design.md, section "Questions only Logius can answer".

Already done

• Spec: docs(openspec): a Berichtenbox client built on the interface Logius publishes #2578. Client built on Logius TAH 1.6.4: feat(berichtenbox): a live MijnOverheid Berichtenbox client, on the interface Logius publishes #2599. Digital post as a service account: feat(digital-post): store digital post as a service account, redact the opt-out log on erasure #2574.
• Decisions D1 to D8 approved on docs(openspec): a Berichtenbox client built on the interface Logius publishes #2578.

What is needed

1. A Logius connection (aansluiting) for the customer organisation: OIN, PKIoverheid certificate, access to the test environment, and a CPA.
2. Answers from Logius to the nine questions in design.md:
   • Q1. Which ebMS profile and Digikoppeling version does the Berichtenbox CPA demand today?
   • Q2. The CPA values for a sender: service, party ids, roles, endpoints, retry schedule, synchronous or asynchronous acknowledgement.
   • Q3. Which wins: S1 says Omschrijving is at most 40 characters, the XSD allows 128. Should the request import the _128ch types file?
   • Q4. May a sender call WUS ValidateAbonnementen once per letter, and at what volume does Logius want the ebMS AbonnementService instead?
   • Q5. How long can a GLOBE-R-BV-Result take?
   • Q6. What does EindDatumHandelingsTermijn trigger? It is in the XSD, not in S1.
   • Q7. Does a new connection on GLOBE have to move to BBO later, and with how much notice?
   • Q8. What does a connection cost, for an organisation and for an intermediary?
   • Q9. Does BerichtBestaatAl on a resend mean the first letter reached the citizen?

Done when

• The answers are recorded in design.md and the code follows them (for example the Omschrijving limit, the CPA values).
• One letter is sent and its result received on the Logius test environment, with the evidence in the PR.

Related: #859 (older Berichtenbox adapter change).