fix(privacy): mask the owner BSN on the cross-owner case lists (RB-03)

Mappers.ToAdminSummaryDto set Owner to the raw BSN. Both consumers are cross-owner lists read by someone who is not the subject — GET /admin/cases and GET /werkvoorraad — while GET /beoordeling/{id}, the detail view of the same data, already masked it. The detail screen showed ******782 and the list one click earlier showed the whole thing. Masked in the mapper rather than at each endpoint, so a third cross-owner list cannot be added that forgets to. MaskTail moves out of Program.cs into Domain/People/Pii.cs: it now has callers in Contracts, Program.cs and (once RB-04 lands) Data, and a second hand-rolled copy is how one of them drifts into leaking. Documented as idempotent, which is what lets /beoordeling/{id} keep its own call — IZaakSource has a second implementation whose Owner is mapped from the OpenZaak zaak identificatie, so that endpoint should not depend on which source answered. No frontend change: all three consumers display the value, and the parse boundaries only require a non-empty string. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
2026-08-27 10:52:29 +02:00
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+# RB-03 — mask the owner BSN on the cross-owner case lists
+
+Status: **implemented** · 2026-08-27 · Source findings: `07-bio2-compliance.md` BIO-003 · `99-backlog.md` RB-03
+
+## What was wrong
+
+`Mappers.ToAdminSummaryDto` set `Owner = a.Owner` — the raw BSN. Two endpoints consume it,
+both cross-owner lists read by someone who is **not** the subject:
+
+- `GET /admin/cases` (`cases:manage`)
+- `GET /werkvoorraad` (`aanvraag:beoordelen`)
+
+`GET /beoordeling/{id}` — the *detail* view of the same data — already masked. So the
+detail screen showed `******782` while the list one click earlier showed the whole BSN.
+
+## What changed
+
+| File                        | Change                                                                            |
+| --------------------------- | ----------------------------------------------------------------------------------- |
+| `Domain/People/Pii.cs`      | **new** — `Pii.MaskTail`, moved out of `Program.cs`                               |
+| `Contracts/Mappers.cs`      | `Owner = Pii.MaskTail(a.Owner, 3)`                                                |
+| `Program.cs`                | local `MaskTail` deleted; two call sites point at `Pii.MaskTail`                  |
+| `AdminCasesTests.cs`        | asserts the masked value and that `DemoOwner` does not appear                     |
+| `WerkvoorraadTests.cs`      | same assertion, replacing the `IsNullOrEmpty` one                                 |
+
+**Masked in the mapper, not at the endpoints.** The point of the ticket is that both
+lists *inherit* it, so a third cross-owner list cannot be added that forgets to mask.
+
+**`MaskTail` moved to `Domain/People/Pii.cs`** because it now has three callers across
+three folders (`Contracts`, `Program.cs`, and `Data` once **RB-04** lands), and a second
+hand-rolled copy is how one of them drifts into leaking. It is documented as idempotent,
+which is what lets `/beoordeling/{id}` keep its own call: `IZaakSource` has a second
+implementation (`OpenZaakZaakSource` → `ZgwZaakMapper`, which maps `Owner` from the zaak
+`identificatie`), so that endpoint's guarantee should not depend on which source answered.
+
+## Blast radius on the frontend — none
+
+Both consumers use the value for display only (`admin-cases.page.ts:101`,
+`beoordeling-view.ts:40`, `werkvoorraad-item-view.ts:28`); the `parse*` boundaries require
+a non-empty string, which a masked BSN still is. Nothing keys, filters or looks up by owner.
+
+## Verification
+
+`dotnet format --verify-no-changes` clean. `dotnet test`: **251 passed, 1 failed** — the
+pre-existing `OpenZaakIntegrationTests.Admin_cases_…`, which needs a live container.