feat(domain): RegistratieVerlopen worker + processor expire on document timeout (refs #102)

Adds RegistratieVerlopenJob, IRegistratieVerlopenClient, the ExpireRegistrationWorker
application handler, and the RegistratieVerlopenProcessor drain loop — the timeout
counterpart to the OpenZaak/escalation worker trios.

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

services/domain/Big.Infrastructure/IExternalWorkerClient.cs

@@ -36,3 +36,19 @@ public interface IBeoordelingEscalatieClient
     /// <summary>Complete an acquired escalation job so its token reaches the escalation end event.</summary>
     Task CompleteBeoordelingEscalatieJobAsync(string jobId, CancellationToken ct = default);
 }
+
+/// <summary>
+/// The document-timeout side of the Workflow Client (S-10a): the <c>RegistratieVerlopen</c>
+/// external-worker jobs parked by the 30-day boundary timer on <c>WachtOpDocumenten</c>. Kept separate
+/// from the other worker ports (interface segregation) so neither the OpenZaak nor escalation worker
+/// sees expiry. Implemented by <see cref="FlowableWorkflowClient"/> — the only code that talks to
+/// Flowable (§8.2, ADR-0017).
+/// </summary>
+public interface IRegistratieVerlopenClient
+{
+    /// <summary>Acquire and lock up to <paramref name="maxJobs"/> <c>RegistratieVerlopen</c> jobs.</summary>
+    Task<IReadOnlyList<RegistratieVerlopenJob>> AcquireRegistratieVerlopenJobsAsync(int maxJobs, CancellationToken ct = default);
+
+    /// <summary>Complete an acquired expiry job so its token reaches the <c>endVerlopen</c> end event.</summary>
+    Task CompleteRegistratieVerlopenJobAsync(string jobId, CancellationToken ct = default);
+}

services/domain/Big.Infrastructure/RegistratieVerlopenProcessor.cs

@@ -0,0 +1,41 @@
+using Big.Application;
+using Microsoft.Extensions.Logging;
+
+namespace Big.Infrastructure;
+
+/// <summary>
+/// One poll tick of the document-timeout worker (S-10a, ADR-0017): acquire the parked
+/// <c>RegistratieVerlopen</c> jobs — the tokens the 30-day boundary timer on <c>WachtOpDocumenten</c>
+/// spawns — expire each correlated registration via the <see cref="ExpireRegistrationWorker"/>, and
+/// complete the job so its token reaches <c>endVerlopen</c>. A job that fails is logged and left
+/// un-completed so Flowable redelivers it (§8.6). Split out from the hosted pump so the
+/// acquire→expire→complete logic is unit-testable without a running host. Mirrors
+/// <see cref="OpenZaakJobProcessor"/> and <see cref="BeoordelingEscalatieProcessor"/>.
+/// </summary>
+public sealed class RegistratieVerlopenProcessor(
+    IRegistratieVerlopenClient client,
+    ExpireRegistrationWorker worker,
+    ILogger<RegistratieVerlopenProcessor> logger)
+{
+    /// <summary>Acquire and process up to <paramref name="maxJobs"/> jobs. Returns the number acquired.</summary>
+    public async Task<int> PumpOnceAsync(int maxJobs, CancellationToken ct = default)
+    {
+        var jobs = await client.AcquireRegistratieVerlopenJobsAsync(maxJobs, ct);
+
+        foreach (var job in jobs)
+        {
+            try
+            {
+                await worker.HandleAsync(job, ct);
+                await client.CompleteRegistratieVerlopenJobAsync(job.JobId, ct);
+            }
+            catch (Exception ex)
+            {
+                // Leave the job un-completed: its lock expires and Flowable redelivers it (§8.6).
+                logger.LogError(ex, "RegistratieVerlopen job {JobId} failed; leaving it for redelivery.", job.JobId);
+            }
+        }
+
+        return jobs.Count;
+    }
+}