# ADR-0032: The werkbak refreshes itself by polling, not by a pushed stream

- **Status:** Accepted
- **Date:** 2026-09-04
- **Deciders:** Respellion engineering
- **Slice:** #162 (proposal #163). The issue titles it S-26; that id already belongs to
  the self-service resume slice (#111), so #162 is the identifier that counts.

## Context

The werkbak (S-12) is a read of the open Flowable `Beoordelen` tasks: portal → BFF
`GET /behandel/werkbak` → domain `Werkbak` query → workflow engine, each task enriched
from its aggregate. A registration reaches `Beoordelen` **asynchronously**, only once the
citizen supplies its documents and the DMN routes it (S-10a) — so it appears in a werkbak
that is already open, and until now a behandelaar had to reload the page to see it.

Three forces shape the mechanism:

- **Nothing notifies anyone.** The trigger lives in Flowable. The domain does not publish
  task events, and there is no bus between the domain and the BFF.
- **The BFF is stateless** and sits behind each portal's reverse proxy.
- **This is the repo's first live-updating view**, so the choice sets a precedent.

## Decision

**The werkbak page re-reads the existing BFF endpoint on a fixed interval
(`WERKBAK_REFRESH_MS`, 5 s) while it is open. No new endpoint, dependency or server-side
state.**

The refresh is a *background* read: it leaves the rows and the loading/failure states
untouched until it has an answer, so a tick never flashes a spinner over rows a
behandelaar is reading and a single failed poll never swaps the list for the error alert.
A read that comes back also clears an earlier failure, so the view recovers on its own —
the same reload this slice set out to remove would otherwise be needed to escape a
transient error. Only a foreground read (on open, after a decision) speaks for whether the
werkbak is readable at all.

### Why not SSE or WebSockets

Neither buys freshness here, because **nothing notifies the BFF either**:

- **SSE** (`text/event-stream`) would mean a new streaming endpoint whose handler polls the
  domain and forwards diffs — the same latency, plus connection lifecycle, proxy
  buffering, and auth on a long-lived connection.
- **WebSocket/SignalR** adds a dependency (CLAUDE.md §13) and makes the BFF stateful and
  sticky-session-bound. A genuine push path would *also* need the domain to publish task
  events. Warranted by high-frequency, bidirectional or fan-out-heavy traffic; the werkbak
  is none of those.

Polling meets the acceptance ("a registration can be seen in the werkbak once it is ready
for review") in a handful of lines inside one component.

- ponytail ceiling: a fixed 5 s interval, per open page, that keeps polling in a
  background tab. Each tick costs one Flowable task query plus a store read per open task.
- Upgrade path: publish task events from the domain, then swap the component's `interval`
  for a stream. The endpoint contract and the component's rendering stay as they are;
  gate on `document.visibilityState` first if request volume is the concern.

## Consequences

**Positive**

- The outcome is delivered with no new endpoint, dependency, or server-side state, and no
  service boundary moves.
- Self-healing: a transient read failure no longer strands the view until a manual reload.
- The e2e got *simpler* — the happy path waits for the werkbak row without reloading the
  page, which is itself the live-refresh assertion.

**Negative / costs**

- Staleness is bounded by one interval (≤5 s) rather than instant.
- One `GET /behandel/werkbak` per open werkbak per interval, including in hidden tabs.
- The precedent is polling; a future view with genuinely high-frequency updates will have
  to revisit this (see the upgrade path above).

## Coupling rules touched (CLAUDE.md §8)

None. The poll reuses the existing portal → BFF → domain read path: §8.3 (portals talk
only to the BFF) and §8.2 (only the Workflow Client talks to Flowable) are unchanged.