diff --git a/docs/testing.md b/docs/testing.md
index 57d6d18070..79d4e53d14 100644
--- a/docs/testing.md
+++ b/docs/testing.md
@@ -217,6 +217,10 @@ FNXC:CoreTests 2026-06-19-15:05: Merge verification re-observed store-concurrent
 
 **2026-06-19 dashboard WorkflowNodeEditor rescue (FN-6744):** `packages/dashboard/app/components/__tests__/WorkflowNodeEditor.test.tsx` was rescued before its 2026-07-03 deletion deadline. The original duplicate-merge test passed in isolation but was load-sensitive because `handleInsertFragment` derived existing seams only from transient React Flow nodes; a fast palette click could arrive after `activeWorkflow.ir` loaded but before the canvas nodes materialized, allowing an invalid duplicate merge seam instead of showing the conflict alert. The fix keeps the test unquarantined by treating IR merge nodes as the merge seam and by unioning seams from the loaded IR only during initial canvas materialization, preserving post-load canvas-state semantics. Regression coverage now exercises both desktop and mobile fragment insertion surfaces and asserts the conflict affordance appears without growing the rendered graph. The ledger and `packages/dashboard/vitest.config.ts` exclude were removed in lockstep; targeted file runs, repeated `test:quality:app:components-b`, lint, gate, typecheck, and build are the closure evidence. A broader `@fusion/dashboard test` run currently fails unrelated Command Center ProductivityArea mock drift tracked by FN-6754, so do not re-quarantine WorkflowNodeEditor for that lane.
 
+<!-- FNXC:DashboardTests 2026-06-19-22:14: FN-6753 classified `routes-auth.test.ts` as suite-load coupled rather than a proven low-value flake: it timed out in the broad dashboard API backfill shard, but repeated loaded local shard runs did not isolate a root-cause teardown or probe-spy leak. Keep auth-critical assertions active by moving the file into the curated dashboard API shard and out of the contended backfill glob; do not quarantine, widen timeouts, retry, or reduce worker load without new root-cause evidence. -->
+
+**2026-06-19 dashboard API shard isolation (FN-6753):** `packages/dashboard/src/__tests__/routes-auth.test.ts` is classified as **suite-load coupling**. The observed symptom was a timeout only under the broad `dashboard-api-quality-backfill` shard; five loaded local runs of the isolated shard did not expose a concrete teardown, probe-spy, or product-code root cause. The remedy is shard isolation, not quarantine: keep `routes-auth` in the curated `dashboard-api-quality` include list so authentication coverage stays active, and let `backfillApiExclude` remove it from the broad `src/**/*.test.ts` backfill glob. Use the same pattern for critical route suites that fail only under broad backfill contention after loaded local proof cannot identify an owned fixture seam: preserve coverage in a curated shard, document the classification, and avoid timeout bumps, retries, worker reductions, or ledger entries unless a later loaded run proves a real flaky file that needs the deletion ratchet.
+
 **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).
diff --git a/packages/dashboard/vitest.config.ts b/packages/dashboard/vitest.config.ts
index 826285a14b..f4e0930893 100644
--- a/packages/dashboard/vitest.config.ts
+++ b/packages/dashboard/vitest.config.ts
@@ -296,7 +296,12 @@ const quarantinedDashboardTests: string[] = [];
 const qualityApiTests = [
   // Critical HTTP/server behavior: auth, task/project/settings mutation,
   // git/GitHub, agents, nodes, chat/files, realtime, and isolation guards.
-  "src/__tests__/{api-error,auth-middleware,auth-middleware-integration,chat-attachment-routes,chat-manager,chat-routes,file-service,github,github-webhooks,initialize,planning-flow-diagnostics-guardrail,pr-routes-auto-merge,pr-routes.contract,project-routes,project-store-resolver,register-git-github.pr-options-preflight-metadata,register-git-github.pr-resolve-conflicts,remote-access-routes,remote-auth,routes-agent-budget,routes-agent-keys,routes-agent-permissions,routes-agent-ratings,routes-agent-runs,routes-agent-soul-memory,routes-agents,routes-automation,routes-branch-groups,routes-git,routes-github,routes-merge-advance-push-origin,routes-nodes,routes-nodes-sync-contract,routes-planning,routes-plugin-registry,routes-secrets-sync,routes-settings,routes-task-commit-associations,routes-tasks,routes-tasks-deterministic-dedup,routes-tasks-duplicate-check,routes-tasks-explicit-duplicate-marker,server,server-static-assets,server-webhook,server.events,setup-routes,sse,sse-buffer,test-isolation-guard,update-check-route,websocket,recover-branch-binding-route}.test.ts",
+  /*
+  FNXC:DashboardTests 2026-06-19-22:14:
+  FN-6753 observed routes-auth timing out only under the broad API backfill shard, while five loaded local shard runs did not expose a concrete probe-spy or teardown root cause.
+  Keep this auth-critical suite in the curated API shard so its assertions remain active without running inside the contended broad backfill glob.
+  */
+  "src/__tests__/{api-error,auth-middleware,auth-middleware-integration,chat-attachment-routes,chat-manager,chat-routes,file-service,github,github-webhooks,initialize,planning-flow-diagnostics-guardrail,pr-routes-auto-merge,pr-routes.contract,project-routes,project-store-resolver,register-git-github.pr-options-preflight-metadata,register-git-github.pr-resolve-conflicts,remote-access-routes,remote-auth,routes-agent-budget,routes-agent-keys,routes-agent-permissions,routes-agent-ratings,routes-agent-runs,routes-agent-soul-memory,routes-agents,routes-auth,routes-automation,routes-branch-groups,routes-git,routes-github,routes-merge-advance-push-origin,routes-nodes,routes-nodes-sync-contract,routes-planning,routes-plugin-registry,routes-secrets-sync,routes-settings,routes-task-commit-associations,routes-tasks,routes-tasks-deterministic-dedup,routes-tasks-duplicate-check,routes-tasks-explicit-duplicate-marker,server,server-static-assets,server-webhook,server.events,setup-routes,sse,sse-buffer,test-isolation-guard,update-check-route,websocket,recover-branch-binding-route}.test.ts",
   "src/__tests__/dashboard-test-config-guard.test.ts",
   "src/routes/__tests__/{custom-provider-routes,custom-providers,register-docker-node-routes,register-diagnostics-routes,stash-recovery-routes}.test.ts",
   "scripts/__tests__/{run-quality-tests,run-vitest-with-heap}.test.ts",