test(workflow): start carries diploma origin as a process variable (S-13, refs #14)

Add DiplomaOrigin (Binnenlands/Buitenlands) to the Registration aggregate and
submit command, and thread it through the process-start port so the workflow's
DMN can route on it (ADR proposal #100). Failing Workflow Client test asserts the
diplomaOrigin start variable; the client takes the origin but does not emit it yet.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

services/domain/Big.Domain/DiplomaOrigin.cs

@@ -0,0 +1,17 @@
+namespace Big.Domain;
+
+/// <summary>
+/// Where a zorgprofessional's diploma was issued. It is the input to the diploma-eligibility decision
+/// (S-13): a <see cref="Buitenlands"/> (foreign) diploma routes the registratie through an extra
+/// CBGV-advies assessment step, a <see cref="Binnenlands"/> (domestic) one goes straight to beoordeling.
+/// The decision itself lives in the workflow's DMN, not here (ADR-0016); the domain only carries the
+/// origin and hands it to the process as a start variable.
+/// </summary>
+public enum DiplomaOrigin
+{
+    /// <summary>A Dutch (domestic) diploma. Default for a registration submitted via DigiD.</summary>
+    Binnenlands,
+
+    /// <summary>A foreign diploma (e.g. an eIDAS submission). Triggers the CBGV-advies step.</summary>
+    Buitenlands,
+}

services/domain/Big.Domain/Registration.cs

@@ -7,10 +7,11 @@ namespace Big.Domain;
 /// </summary>
 public sealed class Registration
 {
-    private Registration(RegistrationId id, string bsn)
+    private Registration(RegistrationId id, string bsn, DiplomaOrigin diplomaOrigin)
     {
         Id = id;
         Bsn = bsn;
+        DiplomaOrigin = diplomaOrigin;
         Status = RegistrationStatus.Ingediend;
     }
 
@@ -20,6 +21,10 @@ public sealed class Registration
     /// as the domain payload; the domain never constructs ZGW concepts from it (§8.1).</summary>
     public string Bsn { get; }
 
+    /// <summary>Where the diploma was issued. Rides along to the process as a start variable and
+    /// drives the diploma-eligibility DMN's foreign→CBGV-advies routing (S-13, ADR-0016).</summary>
+    public DiplomaOrigin DiplomaOrigin { get; }
+
     public RegistrationStatus Status { get; private set; }
 
     /// <summary>The Flowable process instance driving this registration, once started.</summary>
@@ -28,11 +33,13 @@ public sealed class Registration
     /// <summary>The zaak the ACL opened for this registration, once the external task has run.</summary>
     public Uri? ZaakUrl { get; private set; }
 
-    /// <summary>Submit a new registration. It begins in <see cref="RegistrationStatus.Ingediend"/>.</summary>
-    public static Registration Submit(string bsn)
+    /// <summary>Submit a new registration. It begins in <see cref="RegistrationStatus.Ingediend"/>.
+    /// The diploma origin defaults to <see cref="DiplomaOrigin.Binnenlands"/> — the common DigiD path;
+    /// a foreign (eIDAS) submission passes <see cref="DiplomaOrigin.Buitenlands"/>.</summary>
+    public static Registration Submit(string bsn, DiplomaOrigin diplomaOrigin = DiplomaOrigin.Binnenlands)
     {
         ArgumentException.ThrowIfNullOrWhiteSpace(bsn);
-        return new Registration(RegistrationId.New(), bsn);
+        return new Registration(RegistrationId.New(), bsn, diplomaOrigin);
     }
 
     /// <summary>Record that the registratie workflow process has been started for this registration.</summary>