feat(i18n): localize servicedesk errors + guard against un-keyed throws (#16 Phase-2 close-out)

[WolfTasks]

Final session of the #16 backend-i18n Phase-2 API-error sweep (Task 9 servicedesk + sweep close-out). Single commit, TDD-ordered. Branches off clean main — no stacking.

What changed

Localizes the last remaining module + fixes latent 500s. Both servicedesk REST controllers threw ?: error(...) (unhandled IllegalStateException → HTTP 500 for ordinary "unknown project / desk not enabled" conditions) and English-only ResponseStatusException. Converted to the project's keyed domain exceptions:

• ServiceDeskController.kt / IncidentController.kt:
  • 9× ?: error("Project not found…" / "Service desk not enabled…") → NotFoundException.keyed("project.notFound" | "serviceDesk.notEnabled", key) — 500 → localized 404
  • 2× ResponseStatusException(BAD_REQUEST, …) → BadRequestException.keyed("serviceDesk.invalidPriority" | "incident.invalidSeverity", …) — stays 400, now localized body
  • removed now-unused ResponseStatusException import; kept HttpStatus (still used by @ResponseStatus)
• New catalog keys (en base messages.properties + de messages_de.properties, \uXXXX-escaped; project.notFound reused): serviceDesk.notEnabled, serviceDesk.invalidPriority, incident.invalidSeverity (the last doubled ''{0}'' per the MessageFormat rule).

Durable regression guard — NoUnkeyedUserFacingThrowTest. A static gate that fails CI on any un-keyed user-facing throw — bare OR fully-qualified (throw com.taskowolf…NotFoundException("…")) — plus free-text orElseThrow, ?: error(, ResponseStatusException, AccessDeniedException. Allowlists exactly the 2 intentional internal invariants (SsoController clientSecret, OidcUserProvisioningService OIDC-no-email). Closes the FQ-prefix blind spot that let an un-keyed AttachmentController throw slip through the earlier sweep. Has an anti-vacuous check (filesScanned > 0).

Tests

• ServiceDeskMessagesTest — en/de resolution for the 3 new keys (proves the ''{0}'' doubling).
• ServiceDeskErrorLocalizationTest (MockMvc) — unknown project → 404 localized de, desk-not-enabled → 404 localized de, invalid priority → 400 localized, invalid severity → 400 localized.
• Full suite 373/373 green; all three static gates green (MessagesParityTest, KeyedReferenceIntegrityTest, NoUnkeyedUserFacingThrowTest).
• TDD: guard's RED phase listed exactly the 11 servicedesk sites (no false positives); web test RED was 500/unlocalized.

Sweep close-out verification

The plan's widened FQ-blind-spot audit was run against the full src/main/kotlin tree and is clean everywhere except the 2 allowlisted invariants → the #16 Phase-2 API-error sweep is complete.

Reviews

Task review: Approved (0 Critical/Important). Final whole-branch review (opus): Ready to merge: Yes (0 Critical/Important). 3 Minor findings all inherited/pre-existing patterns, correctly deferred.

Handoff (owed by Wolfgang, after merge — out of scope here)

• Manual DE/EN browser smoke: GET a service desk on a project that has none → German 404 (not 500); switch to English → English body; confirm Accept-Language in the Network tab.
• The v1.0.x release.
• Frontend note: GET …/service-desk now returns 404 (not 500) when the desk isn't enabled — treat that as the "not enabled" state. Both project-not-found and not-enabled share code NOT_FOUND (distinguishable by message only).
• Phase 3 (emails + notifications, recipient-locale rendering) remains open.

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