feat(workflow): document-wait task + 30-day timeout cancellation (S-10a, closes #102) (#105)

## What & why

S-10a, the **workflow/timeout spine** of the (split) document-upload slice: the registratie process
now parks at a **`WachtOpDocumenten`** user task with an **interrupting `P30D` boundary timer**. When
the documents arrive the task completes and the process continues into the diploma routing (S-13) →
Beoordelen; if the 30 days lapse, the timer cancels the wait, runs a `RegistratieVerlopen`
external-worker task, and the domain expires the aggregate to a new terminal status **`Verlopen`**.
Backend only — the real upload trigger (portal → BFF → ACL → Documenten API) is S-10b (#103).

Closes #102

Mechanism recorded in **ADR-0017**; opened as proposal #104. Mirrors the S-14 escalation
(boundary-timer + external-worker) and S-11 withdrawal (interrupting cancel) patterns.

## Definition of Done

- [x] Linked Gitea issue (above).
- [x] Failing test committed before the implementation (red→green pairs per layer).
- [x] Implementation makes the test pass.
- [x] Conventional Commits referencing the issue (`refs #102`).
- [ ] CI green — all Gitea Actions jobs (pending on this PR).
- [x] `docker compose up` health unaffected (no new services; deploy path unchanged).
- [x] Docs updated (ADR-0017, demo-script, BACKLOG split).
- [x] ADR added (`docs/architecture/adr-0017-document-wait-timeout-cancellation.md`).
- [x] Demo note in `docs/demo-script.md`.

## Notes for reviewers

- **Domain** (`Registration.Expire()` + `Verlopen`), **application** (`ExpireRegistrationWorker`),
  **infra** (`RegistratieVerlopenProcessor`/`Pump`, `IRegistratieVerlopenClient`, Flowable
  acquire/complete + `CompleteDocumentWaitAsync`) — the timeout counterpart to the OpenZaak/escalation
  worker trios; idempotent per §8.6.
- **BPMN** verified live against a `flowable-rest` probe: complete `WachtOpDocumenten` → routes to
  Beoordelen; fire the P30D timer → `RegistratieVerlopen` job (carrying `registrationId`) + the wait
  task cancelled. `verify-domain` exercises both branches in-stack (completes the wait in every existing
  block; fires the timer and asserts `Verlopen` in a new block).
- **Scope boundary:** on expiry the aggregate goes `Verlopen` and the process ends, but the ZGW *zaak*
  is not yet set to a cancellation status — that needs a new ACL method + statustype seeding and is
  folded into S-10b (noted in ADR-0017).
- `CompleteDocumentWaitAsync` is built and HTTP-tested here but not yet called from a domain endpoint;
  S-10b wires the upload trigger to it.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: #105

services/domain/Big.Tests/FlowableWorkflowClientTests.cs

@@ -426,4 +426,106 @@ public class FlowableWorkflowClientTests
             capture.Seen.RequestUri!.ToString());
         Assert.Contains("\"workerId\":\"worker-x\"", capture.Body);
     }
+
+    // ── S-10a (#102): document-wait timeout → RegistratieVerlopen (ADR-0017) ──────────────────────
+    // A 30-day interrupting boundary timer on WachtOpDocumenten spawns a RegistratieVerlopen
+    // external-worker job carrying the registration id; the worker expires the registration and
+    // completes the job. Separately, "documents received" completes the WachtOpDocumenten user task.
+
+    [Fact]
+    public async Task Acquire_verlopen_jobs_posts_the_topic_and_parses_jobs_with_their_registration_id()
+    {
+        var rid = RegistrationId.New();
+        var capture = new RequestCapture();
+        var client = Client(capture.Responds(HttpStatusCode.OK,
+            $$"""[{"id":"job-9","variables":[{"name":"registrationId","type":"string","value":"{{rid}}"}]}]"""));
+
+        var jobs = await client.AcquireRegistratieVerlopenJobsAsync(3);
+
+        var job = Assert.Single(jobs);
+        Assert.Equal("job-9", job.JobId);
+        Assert.Equal(rid, job.RegistrationId);
+        Assert.Equal("http://flowable/flowable-rest/external-job-api/acquire/jobs",
+            capture.Seen!.RequestUri!.ToString());
+        Assert.Contains("\"topic\":\"RegistratieVerlopen\"", capture.Body);
+        Assert.Contains("\"numberOfTasks\":3", capture.Body);
+        Assert.Contains("\"workerId\":\"worker-x\"", capture.Body);
+    }
+
+    [Theory]
+    [InlineData("[]")]
+    [InlineData("null")]
+    public async Task Acquire_verlopen_jobs_returns_empty_when_none_are_parked(string body)
+    {
+        var capture = new RequestCapture();
+        var client = Client(capture.Responds(HttpStatusCode.OK, body));
+
+        Assert.Empty(await client.AcquireRegistratieVerlopenJobsAsync(1));
+        Assert.NotNull(capture.Seen);
+    }
+
+    [Fact]
+    public async Task Complete_verlopen_job_posts_to_the_job_complete_endpoint()
+    {
+        var capture = new RequestCapture();
+        var client = Client(capture.Responds(HttpStatusCode.NoContent));
+
+        await client.CompleteRegistratieVerlopenJobAsync("job-9");
+
+        Assert.Equal(HttpMethod.Post, capture.Seen!.Method);
+        Assert.Equal("http://flowable/flowable-rest/external-job-api/acquire/jobs/job-9/complete",
+            capture.Seen.RequestUri!.ToString());
+        Assert.Contains("\"workerId\":\"worker-x\"", capture.Body);
+    }
+
+    [Fact]
+    public async Task Provide_documents_completes_the_wacht_op_documenten_task_in_the_instance()
+    {
+        var requests = new List<(HttpMethod Method, string Url, string? Body)>();
+        var client = Client(new StubHandler(async req =>
+        {
+            requests.Add((req.Method, req.RequestUri!.ToString(),
+                req.Content is null ? null : await req.Content.ReadAsStringAsync()));
+            return req.RequestUri!.AbsoluteUri.EndsWith("service/query/tasks")
+                ? new HttpResponseMessage(HttpStatusCode.OK)
+                {
+                    Content = new StringContent("""{"data":[{"id":"task-3"}],"total":1}""",
+                        Encoding.UTF8, "application/json"),
+                }
+                : new HttpResponseMessage(HttpStatusCode.OK);
+        }));
+
+        await client.CompleteDocumentWaitAsync("pi-1");
+
+        // 1. Find the still-open WachtOpDocumenten task in this process instance.
+        var query = requests.Single(r => r.Url.EndsWith("service/query/tasks"));
+        Assert.Equal(HttpMethod.Post, query.Method);
+        Assert.Contains("\"processInstanceId\":\"pi-1\"", query.Body);
+        Assert.Contains("\"taskDefinitionKey\":\"WachtOpDocumenten\"", query.Body);
+        // 2. Complete that task so the process leaves the wait state.
+        var complete = requests.Single(r => r.Url.EndsWith("service/runtime/tasks/task-3"));
+        Assert.Equal(HttpMethod.Post, complete.Method);
+        Assert.Contains("\"action\":\"complete\"", complete.Body);
+    }
+
+    [Fact]
+    public async Task Provide_documents_is_a_no_op_when_the_wait_task_is_no_longer_open()
+    {
+        // The process already left WachtOpDocumenten (e.g. timed out): nothing to complete, no throw.
+        var methods = new List<HttpMethod>();
+        var client = Client(new StubHandler(req =>
+        {
+            methods.Add(req.Method);
+            return Task.FromResult(new HttpResponseMessage(HttpStatusCode.OK)
+            {
+                Content = new StringContent("""{"data":[],"total":0}""", Encoding.UTF8, "application/json"),
+            });
+        }));
+
+        await client.CompleteDocumentWaitAsync("pi-1");
+
+        // Only the query ran; no task-completion POST followed.
+        Assert.DoesNotContain(methods, m => m == HttpMethod.Put || m == HttpMethod.Delete);
+        Assert.Single(methods);
+    }
 }