# WP-65 — Behandelportal: zaak detail + beoordeling (decision) screen

Status: todo
Phase: 11 — Behandelportal

## Why

The core case-treatment write path — a medewerker opens one aanvraag's detail (including
its documents) and records a decision (goedkeuren/afwijzen/meer info opvragen), advancing
the status lifecycle WP-63 published. This is the first genuinely new *write* capability
in the system beyond what the citizen SSP already does to itself.

## Read first

- `mutation-command` skill
- `form-machine` skill (the decision action is a state-changing form, same idiom as
  everywhere else in this house)
- [WP-63](WP-63-aanvraag-status-lifecycle.md) (the status field being advanced)

## Decisions (pre-made, don't relitigate)

- The decision action is modeled as a `*.machine.ts` (Model/Msg/reduce) + a `submit-*`
  command returning `Result`, per this house's one-idiom-for-forms rule — not a
  hand-rolled mutable field.
- The mutation endpoint is a new BFF-lite write (per `mutation-command` recipe) that
  transitions the status field from WP-63; it validates the transition is legal
  server-side (e.g. can't approve an already-approved case) — the backend remains the
  authority.
- Runs against `LocalZaakSource` for this slice; wiring the decision into real OpenZaak is
  explicitly WP-66, not bundled here — keeps this slice's surface to app-level behavior
  only.

## Files

New mutation endpoint + command in `BigRegister.Api`; `behandeling/ui` detail page +
`behandeling/application` decision machine in the behandelportal app.

## Steps

1. Backend: mutation endpoint advancing aanvraag status (goedkeuren/afwijzen/meer-info-
   opvragen), validating the transition.
2. FE: zaak-detail page (documents + current status) + a decision form machine + submit
   command.
3. Wire the werkvoorraad list (WP-64) to link into this detail page.
4. Storybook stories + a11y for the new detail/decision UI.

## Acceptance criteria

- [ ] A medewerker can view one aanvraag's detail and record a decision that advances its
      status.
- [ ] Illegal transitions are rejected server-side (tested).
- [ ] End-to-end smoke: werkvoorraad → detail → decision → status change reflected back
      in the queue.
- [ ] `npm run ci` (behandelportal app) + `dotnet test` green.

## Verification

Manual/automated smoke test of the full werkvoorraad → beoordeling → besluit flow against
`LocalZaakSource`; `npm run ci`; `cd backend && dotnet test`.

## Out of scope

Writing the decision to real OpenZaak (WP-66).

## Risks

This is the largest FE slice in Phase 11 — if it feels too big at kickoff, split
detail-view (read) from decision-recording (write) into two sessions; the WP as scoped
already keeps them in one slice because a detail view with no decision action isn't
independently useful for a caseworker.

Depends on: WP-64.