[AZ-463] [AZ-469] [AZ-476] [AZ-477] Batch 6 - flight/responsive/upload/settings tests

- AZ-463 flight selection persistence (FT-P-16) + rehydration
  on boot (FT-P-17) PASS at the wire; 100-cycle leak guard
  (NFT-RES-LIM-07) and 1h SSE soak (NFT-RES-LIM-06)
  scaffolded as RUN_LONG_RUNNING-gated e2e companions.
- AZ-469 browser-support smoke (FT-P-34) runs in both
  Chromium and Firefox via the existing playwright config;
  responsive variants (FT-P-35 480px / FT-P-36 1024px) PASS
  in fast (Tailwind class shape) and e2e (visibility).
- AZ-476 upload 501 MB -> 413: AC-1 user-visible error is
  drift today (uploadFiles silently falls through to local
  mode); it.fails() + control + e2e test.fail. AC-2 no-alert
  PASS via dialog spy.
- AZ-477 settings save 500 / network drop: AC-1+AC-2+AC-3
  all drift today (no try/finally, no error region, deadline
  unmeasurable); 4 it.fails() + control pinning the stuck-
  disabled drift; e2e companions test.fail mirror it.
- LESSONS.md seeded: vi.stubGlobal('URL', {...URL,...})
  destroys the URL constructor and breaks new URL(...) in
  MSW; patch the methods directly instead.

Code review: PASS (0 findings). Fast: 22/22 files, 120
passed / 13 skipped. Static: 24/24 PASS.

Co-authored-by: Cursor <cursoragent@cursor.com>

_docs/02_tasks/done/AZ-477_test_settings_resilience.md

@@ -0,0 +1,53 @@
+# Test — Settings Save Resilience & 2 s Error Budget
+
+**Task**: AZ-477_test_settings_resilience
+**Name**: Settings save 500 + network drop — `saving` flag reset + error surfaces ≤ 2 s
+**Description**: Implement the 5 blackbox tests covering Settings save resilience: upstream 500, network drop, the 2-second error-surface deadline, and the try/finally state reset that prevents a stuck "saving…" indicator.
+**Complexity**: 3 points
+**Dependencies**: AZ-456_test_infrastructure
+**Component**: 09_settings (Blackbox Tests)
+**Tracker**: AZ-477
+**Epic**: AZ-455
+
+## Problem
+
+Settings save has been observed to leave the `saving` flag set after an upstream failure (annotated in `src__features__settings__SettingsPage.md`). The user sees a forever-spinning button and the page becomes unusable. The contract: on ANY failure (HTTP error or network error), state resets within 2 s AND a user-visible error appears.
+
+## Outcome
+
+- 5 scenarios pass.
+
+## Scope
+
+### Included
+
+| Scenario | Profile | Source file |
+|----------|---------|-------------|
+| FT-N-13 — Settings save with 500 response — `saving` flag reset; error surfaced | fast | blackbox-tests.md |
+| FT-N-14 — Settings save with network failure — try/finally state reset | fast | blackbox-tests.md |
+| NFT-PERF-09 — Settings save error surfaces within 2 s | fast | performance-tests.md |
+| NFT-RES-05 — Settings save with upstream 500 — UI state recovers | fast | resilience-tests.md |
+| NFT-RES-06 — Settings save with network drop — try/finally state reset | fast | resilience-tests.md |
+
+### Excluded
+
+- Settings happy path (covered by per-feature tests in Phase B).
+- Settings RBAC redirect (covered in 12_test_protected_route_rbac).
+
+## Acceptance Criteria
+
+**AC-1: 500 recovery**
+FT-N-13 / NFT-RES-05 — MSW returns 500 on settings PUT; assert: (a) `saving` flag is off (Save button no longer disabled / spinner not shown) within 2 s, (b) an error region is present in DOM.
+
+**AC-2: Network drop**
+FT-N-14 / NFT-RES-06 — MSW returns a network error; assert the same two conditions as AC-1.
+
+**AC-3: Deadline**
+NFT-PERF-09 — measure wall-clock from response receipt (or network failure) to DOM error visibility; assert ≤ 2 s.
+
+## System Under Test Boundary
+
+- System under test: `<SettingsPage>` + its save handler + `src/api/client.ts`.
+- Allowed stubs: MSW for the settings PUT endpoint (returns 500 / network error per scenario).
+- Disallowed: reading React state — test asserts DOM affordances (disabled button, error region).
+- Expected observables per `results_report.md` rows 68-70 + the rows for NFT-RES-05/06.