FN-6514: restore QuickEntryBox test isolation

Rescues the QuickEntryBox suite by restoring jsdom globals instead of keeping it quarantined.

- Snapshot and restore QuickEntryBox viewport, visibility, matchMedia, and object URL descriptors after each test.
- Add a guard test that proves mutated jsdom globals return to their original descriptors.
- Remove the QuickEntryBox quarantine entries while documenting the rescue pattern.

Files changed:
 docs/testing.md                                    |  2 +
 .../components/__tests__/QuickEntryBox.test.tsx    | 50 ++++++++++++++++++++++
 packages/dashboard/vitest.config.ts                |  7 ++-
 scripts/lib/test-quarantine.json                   |  5 ---
 4 files changed, 55 insertions(+), 9 deletions(-)

Fusion-Task-Id: FN-6514

Fusion-Task-Lineage: 12f20ad8-19ee-4168-91a9-33193b1ab5f7

docs/testing.md

@@ -162,6 +162,8 @@ Legitimate legacy exceptions must be recorded in `scripts/lib/test-timeout-appea
 
 **2026-06-15 rescue batch (FN-6486):** two same-day quarantines were rescued before their 2026-06-29 deletion deadline. `store-concurrent-writes.test.ts` kept its WAL/`transactionImmediate` regression value by making the external lock helper's timed release use synchronous `Atomics.wait` inside the child process, removing event-loop timer scheduling as the load-only flake source without widening retry windows. `extension-task-tools.test.ts` kept its worktree-root task-tool coverage by closing each real `TaskStore` fixture before temp-root removal and using non-hoisted mock cleanup. The reusable pattern is to remove scheduler/resource leaks in the helper or fixture seam, then prove the rescue with repeated exact-file runs plus package lanes, not with timeout bumps, retries, assertion loosening, or worker changes.
 
+**2026-06-16 rescue (FN-6514):** `packages/dashboard/app/components/__tests__/QuickEntryBox.test.tsx` was rescued before its 2026-06-30 deletion deadline. The file still caught real quick-entry behavior regressions, but it leaked jsdom descriptors for `window.innerWidth`, `window.matchMedia`, `document.visibilityState`, `URL.createObjectURL`, and `URL.revokeObjectURL`; a mobile viewport helper could leave later tests in the same dashboard backfill shard observing `innerWidth=375` and mismatched responsive assertions. The rescue removed the ledger/config quarantine entries in lockstep, captured each original `PropertyDescriptor` at module load, restored those descriptors (or deleted own properties that were originally absent) in `afterEach`, and added a guard test that mutates all rescued globals before asserting they return to their original descriptors. Reusable pattern: any test file that changes jsdom globals with `Object.defineProperty` or spies on replaceable globals must snapshot the original descriptor at the top of the file, restore it in every `afterEach`, and prove the invariant with a guard test; do not use timeout bumps, retries, worker changes, or blanket `vi.restoreAllMocks()` when module mocks depend on stable implementations.
+
 **Gate eviction:** a flake inside the merge gate cannot block all merges while red — it is evicted by removing its line from the `engine-core` allow-list (no quarantine entry needed unless it should also leave the non-blocking tier).
 
 **Gate admission:** the mirror operation — add the test's path to the `engine-core` `include` array in `packages/engine/vitest.config.ts`, citing the evidence of value (a real regression it caught) in the PR. Keep the project under its ~60s wall-clock budget.

packages/dashboard/app/components/__tests__/QuickEntryBox.test.tsx

@@ -28,6 +28,39 @@ const TEST_PROJECT_ID = "proj-123";
 const QUICK_ENTRY_STORAGE_KEY = scopedKey("kb-quick-entry-text", TEST_PROJECT_ID);
 const QUICK_ENTRY_BOX_CSS = readFileSync("app/components/QuickEntryBox.css", "utf8");
 
+const originalWindowInnerWidthDescriptor = Object.getOwnPropertyDescriptor(window, "innerWidth");
+const originalWindowMatchMediaDescriptor = Object.getOwnPropertyDescriptor(window, "matchMedia");
+const originalDocumentVisibilityStateDescriptor = Object.getOwnPropertyDescriptor(document, "visibilityState");
+const originalCreateObjectURLDescriptor = Object.getOwnPropertyDescriptor(URL, "createObjectURL");
+const originalRevokeObjectURLDescriptor = Object.getOwnPropertyDescriptor(URL, "revokeObjectURL");
+
+function restoreDescriptor(target: object, property: PropertyKey, descriptor: PropertyDescriptor | undefined) {
+  if (descriptor) {
+    Object.defineProperty(target, property, descriptor);
+    return;
+  }
+
+  delete (target as Record<PropertyKey, unknown>)[property];
+}
+
+function restoreQuickEntryTestGlobals() {
+  restoreDescriptor(window, "innerWidth", originalWindowInnerWidthDescriptor);
+  restoreDescriptor(window, "matchMedia", originalWindowMatchMediaDescriptor);
+  restoreDescriptor(document, "visibilityState", originalDocumentVisibilityStateDescriptor);
+  restoreDescriptor(URL, "createObjectURL", originalCreateObjectURLDescriptor);
+  restoreDescriptor(URL, "revokeObjectURL", originalRevokeObjectURLDescriptor);
+}
+
+function expectQuickEntryTestGlobalsRestored() {
+  expect(Object.getOwnPropertyDescriptor(window, "innerWidth")).toEqual(originalWindowInnerWidthDescriptor);
+  expect(Object.getOwnPropertyDescriptor(window, "matchMedia")).toEqual(originalWindowMatchMediaDescriptor);
+  expect(Object.getOwnPropertyDescriptor(document, "visibilityState")).toEqual(
+    originalDocumentVisibilityStateDescriptor,
+  );
+  expect(Object.getOwnPropertyDescriptor(URL, "createObjectURL")).toEqual(originalCreateObjectURLDescriptor);
+  expect(Object.getOwnPropertyDescriptor(URL, "revokeObjectURL")).toEqual(originalRevokeObjectURLDescriptor);
+}
+
 function quickEntryMobileActionsTouchRule() {
   return (
     QUICK_ENTRY_BOX_CSS.match(
@@ -336,6 +369,23 @@ describe("QuickEntryBox", () => {
     });
     vi.useRealTimers();
     localStorage.clear();
+    restoreQuickEntryTestGlobals();
+  });
+
+  /*
+  FNXC:DashboardTestIsolation 2026-06-16-21:31:
+  QuickEntryBox runs in broad dashboard jsdom workers, so viewport, visibility, and object-URL mocks must restore their original descriptors after every test.
+  This keeps mobile `innerWidth`/`matchMedia` state from flipping later disclosure `aria-expanded` assertions under sibling-file load.
+  */
+  it("restores jsdom globals mutated by viewport and URL helpers", () => {
+    mockMobileViewport();
+    Object.defineProperty(document, "visibilityState", { configurable: true, value: "visible" });
+    Object.defineProperty(URL, "createObjectURL", { configurable: true, writable: true, value: vi.fn() });
+    Object.defineProperty(URL, "revokeObjectURL", { configurable: true, writable: true, value: vi.fn() });
+
+    restoreQuickEntryTestGlobals();
+
+    expectQuickEntryTestGlobalsRestored();
   });
 
   it("renders textarea with placeholder", () => {

packages/dashboard/vitest.config.ts

@@ -236,16 +236,15 @@ FNXC:DashboardTestQuarantine 2026-06-14-17:01:
 FN-6454 applied the quarantine deletion ratchet to every dashboard test quarantined on 2026-06-14.
 Keep this list empty until a new flaky dashboard test is quarantined with a matching ledger entry.
 
-FNXC:DashboardTestQuarantine 2026-06-16-18:59:
-FN-6496 verification observed QuickEntryBox expanded-mode assertions fail only in the workspace gate while an isolated file rerun passed.
-Quarantine the file under the deletion ratchet instead of appeasing timing/state leakage with retries or widened waits.
+FNXC:DashboardTestQuarantine 2026-06-16-21:31:
+FN-6514 rescued QuickEntryBox before the 2026-06-30 deletion deadline by restoring its mutated jsdom viewport, visibility, and object-URL globals in file teardown.
+Keep it out of this exclude list so the broad app backfill lane exercises its aria-expanded regression coverage without quarantine drift.
 
 FNXC:DashboardTestQuarantine 2026-06-16-19:21:
 FN-6496 merge verification observed github-tracking-hook fail during the changed-test backfill shard with temp-directory cleanup ENOTEMPTY, then pass on isolated rerun.
 Quarantine the cleanup-flaky file under the deletion ratchet rather than changing production or test timing outside the chat-streaming scope.
 */
 const quarantinedDashboardTests: string[] = [
-  "app/components/__tests__/QuickEntryBox.test.tsx",
   "src/__tests__/github-tracking-hook.test.ts",
 ];
 

scripts/lib/test-quarantine.json

@@ -1,11 +1,6 @@
 {
   "$comment": "Flaky-test quarantine ledger (deletion ratchet — see AGENTS.md 'Flaky tests: quarantine on sight' and docs/testing.md 'Quarantine ledger and the deletion ratchet'). A test observed failing without a corresponding real bug is quarantined ON SIGHT: add an entry here AND a matching one-line `exclude` entry in that package's vitest config, in the same commit. Every entry needs a non-empty `reason` (link the failing run) and a `quarantinedAt` date — the entry expires 14 days later, at which point the test file is DELETED unless someone rescues it with evidence it catches real regressions plus a root-cause fix (never appeasement). There is deliberately no loader module and no automation around this file: it is a dated record, the vitest config exclude is the mechanism, and the sweep is policy executed by whoever touches the suite.",
   "entries": [
-    {
-      "file": "packages/dashboard/app/components/__tests__/QuickEntryBox.test.tsx",
-      "reason": "FN-6496 verification: pnpm test failed in QuickEntryBox expanded-mode tests (expected aria-expanded=false, received true) while FN-6496 only changed chat streaming hooks; direct isolated rerun of this file passed, so classify as unrelated flaky state leakage. Failing command: pnpm test; confirming command: pnpm --filter @fusion/dashboard exec vitest run app/components/__tests__/QuickEntryBox.test.tsx --reporter=dot --silent=passed-only.",
-      "quarantinedAt": "2026-06-16"
-    },
     {
       "file": "packages/dashboard/src/__tests__/github-tracking-hook.test.ts",
       "reason": "FN-6496 merge verification: pnpm test failed in dashboard-api-quality-backfill with ENOTEMPTY while removing a temp task directory; isolated rerun of the file passed, so classify as unrelated cleanup flake. Failing command: pnpm test; confirming command: pnpm --filter @fusion/dashboard exec vitest run src/__tests__/github-tracking-hook.test.ts --reporter=dot --silent=passed-only.",