## What & why
Second sub-slice of **S-11 · Withdrawal (Flow 3)** (#12). S-11a (#88) made a withdrawal advance the aggregate to INGETROKKEN; this sub-slice **cancels the running Flowable process** so the withdrawn case leaves the behandelaar's werkbak.
- **BPMN** (`registratie.bpmn`): an interrupting message boundary event (`RegistratieIngetrokken`) on the `Beoordelen` task, routing to a dedicated "Registratie ingetrokken" end event.
- **Workflow Client**: `WithdrawBeoordelingAsync(executionId)` delivers `messageEventReceived` to the task's execution (PUT); `BeoordelingTask` now carries its `executionId`.
- **`WithdrawRegistration` handler**: after the domain transition, finds the open `Beoordelen` task for the registration and delivers the withdrawal message — best-effort, mirroring how the beoordeling completes its task.
- **Werkbak**: also filters out registrations that are no longer open, so a withdrawn case never surfaces even in the brief window before cancellation lands.
- **ADR-0014** records the decision (message event in BPMN vs. deleting the instance from code).
- **verify (`run-domain-check.sh`)**: a second registration parks at `Beoordelen`, is withdrawn via the domain, and the check asserts its `Beoordelen` task disappears — so verify-stack validates the live Flowable message correlation.
Refs #12 (S-11c — the BFF + self-service "trek aanvraag in" button + e2e — closes it).
## Definition of Done
- [x] Linked Gitea issue (#12).
- [x] Failing tests committed before the implementation (red → green per commit).
- [x] Implementation makes the tests pass.
- [x] Conventional Commits referencing the issue (`refs #12`).
- [ ] CI green — all Gitea Actions jobs.
- [x] `docker compose up` unaffected (BPMN redeploys on a fresh CI DB via flowable-init).
- [x] ADR added (ADR-0014).
- [x] Docs — the user-visible demo note lands with S-11c.
## Notes for reviewers
- Verified locally: `Big.Tests` 94/94 pass; `Big.Api` builds; `registratie.bpmn` is well-formed.
- The Flowable message-correlation REST shape is validated **live** by verify-stack (the Workflow Client unit tests stub the exchange and assert only the request shape, per ADR-0009) — the new `run-domain-check.sh` withdrawal step is that live check.
- Known gap (ADR-0014): a withdrawal that races ahead of the process reaching `Beoordelen` finds no task to cancel; the aggregate is still INGETROKKEN and the werkbak filter hides it, but that instance parks unattended. A process-level event subprocess would close the gap — deferred.
Reviewed-on: #89
## What & why
Second sub-slice of **S-12 (#13)** — the **Workflow Client gains behandelaar user-task operations**, and the process model gains the beoordeling step.
- **BPMN:** `registratie.bpmn` now parks at a `Beoordelen` **userTask** (candidate group `behandelaar`) after `OpenZaakAanmaken`; `registrationId` rides along as a process variable so the werkbak can correlate each task to its aggregate.
- **Workflow Client** (`IUserTaskClient`, the only code that talks to Flowable §8.2):
- `GetOpenBeoordelingenAsync()` — the werkbak (open `Beoordelen` tasks + their `registrationId`)
- `ClaimAsync(taskId, behandelaar)`
- `CompleteBeoordelingAsync(taskId, besluit)` — carries the decision into the process as the `besluit` variable
- **Live integration:** `verify-domain` now drives the full user-task lifecycle against a real Flowable — after the worker opens the zaak, it polls for the task, claims it as `merel-behandelaar`, completes it (`goedkeuren`), and asserts the process finishes. This proves the exact REST contract (`service/runtime/tasks/query` + `…/{id}` claim/complete) the client depends on.
The walking skeleton is unaffected: the temporary `/approve` path still sets the zaak status directly; wiring the domain decision to *complete this task* (and driving the werkbak from the BFF) lands in **S-12c**.
## Definition of Done
- [x] Linked issue: #13 (umbrella; `refs`, does not close)
- [x] Tests first; red → green
- [x] Unit + acceptance green (`make unit`): domain 76, acceptance 9 (acl/event-subscriber/bff unaffected)
- [x] Mutation ≥ break(90): **domain 100%** (killed the new survivors *and* the pre-existing `FlowableWorkflowClient` baseline)
- [x] Live Flowable user-task lifecycle asserted in `verify-domain`
- [ ] CI green (pending)
Part of #13.
Reviewed-on: #83
