docs/architecture/adr-0014-withdrawal-cancels-the-process.md

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+# ADR-0014: Withdrawal cancels the registratie process via a BPMN message event
+
+- **Status:** Accepted
+- **Date:** 2026-07-16
+- **Deciders:** Respellion engineering
+- **Relates to:** S-11 (#12); builds on ADR-0009 (external-task worker / Workflow Client), ADR-0013
+  (behandel-portal wiring, the Beoordelen user task)
+
+## Context
+
+S-11 lets a zorgprofessional withdraw a still-open registration ("trek aanvraag in"). S-11a already
+advances the aggregate to INGETROKKEN (domain state). But the registratie process is still running in
+Flowable — parked at the `Beoordelen` user task — so without a second step the withdrawn registration
+would linger as work for a behandelaar. The withdrawal must also **cancel the running process**.
+
+Two questions shape this sub-slice.
+
+1. **How does the case get cancelled — in code, or in the BPMN model?**
+2. **How does a withdrawal correlate to the right running process instance?**
+
+## Decision
+
+**The BPMN models the cancellation as an interrupting message boundary event on the `Beoordelen`
+task; the Workflow Client correlates a `RegistratieIngetrokken` message to the task's execution.**
+
+- **Modelled in BPMN, not deleted from code.** The `Beoordelen` user task carries an interrupting
+  message boundary event (`RegistratieIngetrokken`) that routes to a dedicated "Registratie
+  ingetrokken" end event. The process's own model says *how* a withdrawal ends it — the Workflow
+  Client only delivers the message; it never reaches into Flowable to delete an instance. This keeps
+  the workflow's control flow in the workflow (§8.2) and leaves an audit trail in Flowable history
+  (the process ended via the ingetrokken path, not a raw delete).
+- **Correlated via the Beoordelen task's execution.** The `WithdrawRegistration` handler already
+  knows the registration; it finds the open `Beoordelen` task for it (the same task-query the werkbak
+  uses, §8.2) and asks the Workflow Client to deliver the withdrawal message to that task's execution
+  (`messageEventReceived`). No separate correlation store is needed — the werkbak task set is the
+  authoritative correlation, exactly as the beoordeling decision reuses it (ADR-0013).
+- **Best-effort, mirroring the beoordeling.** If no open `Beoordelen` task is found (the process has
+  not yet parked there — the `OpenZaakAanmaken` window — or has already ended), the withdrawal still
+  stands: the aggregate is INGETROKKEN and the werkbak filters it out regardless (S-11b). We complete
+  the domain transition first and cancel the workflow best-effort, exactly as `BeoordeelRegistratie`
+  completes its task best-effort.
+
+## Consequences
+
+**Positive**
+
+- The cancellation path is visible in `registratie.bpmn`; the Workflow Client stays the only code
+  that talks to Flowable and does not delete instances behind the model's back.
+- Reuses the existing task-query correlation — no new plumbing, no correlation store.
+- A withdrawn case leaves the werkbak (its `Beoordelen` task is cancelled), and the werkbak also
+  filters non-open registrations as a belt-and-braces for the brief window before cancellation lands.
+
+**Negative / costs**
+
+- A withdrawal raced ahead of the process reaching `Beoordelen` (during `OpenZaakAanmaken`, seconds)
+  finds no task to cancel, so that process instance runs on to `Beoordelen` and parks there with no
+  one to act on it (it is hidden from the werkbak by the status filter). Acceptable for this
+  reference at these volumes; a process-level interrupting event subprocess would close the gap and
+  is an additive follow-up if it matters.
+- The Flowable message-correlation REST shape is validated live (verify-stack), not in the
+  Workflow Client's unit tests, which stub the HTTP exchange and assert only the request shape
+  (consistent with ADR-0009).
+
+## Alternatives considered
+
+- **Delete the process instance from the Workflow Client** (`DELETE /runtime/process-instances/{id}`)
+  — rejected: it cancels the case but hides the reason from the BPMN model; the "why" lives in code,
+  not the process. The message event keeps the cancellation a first-class part of the workflow.
+- **Interrupting message event subprocess at process level** — more robust (correlates anytime,
+  closing the `OpenZaakAanmaken`-race gap), but a heavier BPMN construct; deferred as an additive
+  change if the race proves to matter.