diff --git a/packages/engine/vitest.config.ts b/packages/engine/vitest.config.ts
index 8c1e19a9e7..340dd6d5be 100644
--- a/packages/engine/vitest.config.ts
+++ b/packages/engine/vitest.config.ts
@@ -105,6 +105,7 @@ export default defineConfig({
             "src/__tests__/merger-ai-cleanup-active-session.test.ts",
             "src/__tests__/merger-ai-cleanup.test.ts",
             "src/__tests__/merger-ai.test.ts",
+            "src/__tests__/sandbox/bubblewrap-backend.test.ts",
           ],
         },
       },
@@ -115,7 +116,10 @@ export default defineConfig({
           include: ["src/__tests__/reliability-interactions/**/*.test.ts"],
           // Mirror the engine-default exclusion so reliability slow tests
           // also tier into engine-slow.
-          exclude: ["src/**/*.slow.test.ts"],
+          exclude: [
+            "src/**/*.slow.test.ts",
+            "src/__tests__/reliability-interactions/soft-delete-blocker-residue.test.ts",
+          ],
           // These tests assert event ordering across real worktrees. Parallel
           // execution under merger load caused subprocess-guard timeouts and
           // SQLite rowid interleaving (e.g. FN-5521 hit
diff --git a/scripts/lib/test-quarantine.json b/scripts/lib/test-quarantine.json
index 0af4050e92..c4ca79422e 100644
--- a/scripts/lib/test-quarantine.json
+++ b/scripts/lib/test-quarantine.json
@@ -20,6 +20,16 @@
       "file": "packages/dashboard/app/components/__tests__/QuickEntryBox.test.tsx",
       "reason": "Flake observed during FN-6239 verification: broad `pnpm test` in dashboard backfill shard 4/4 could not find `quick-entry-priority-button` immediately after a successful task creation, while the named test passed standalone. Indicates suite-order/concurrency sensitivity unrelated to QuickChatFAB coverage.",
       "quarantinedAt": "2026-06-11"
+    },
+    {
+      "file": "packages/engine/src/__tests__/reliability-interactions/soft-delete-blocker-residue.test.ts",
+      "reason": "Flake observed during FN-6294 verification and reproduced during FN-6319 broad `pnpm --filter @fusion/engine test`: `clearStaleBlockedBy handles missed task:deleted event with soft-deleted-blocker reason` failed because the log entry was absent, while the same file passed standalone and the narrow three-file reproduction passed. Product-code cross-check: `clearStaleBlockedBy` still has the soft-deleted-blocker branch and soft-delete-deadlock-scan-exclusion.test.ts covers it via a deterministic store double, indicating suite-order/concurrency sensitivity in this reliability-interactions fixture rather than a confirmed product bug.",
+      "quarantinedAt": "2026-06-12"
+    },
+    {
+      "file": "packages/engine/src/__tests__/sandbox/bubblewrap-backend.test.ts",
+      "reason": "Flake observed during FN-6294 verification: `attempts bwrap execution when available` timed out in the broad and narrow engine runs, while the file passed standalone during FN-6319. The test mocks detectBwrap as available with path `bwrap` and then invokes real bwrap execution, making it host/environment sensitive when a real bwrap binary is unavailable or behaves differently under suite load.",
+      "quarantinedAt": "2026-06-12"
     }
   ]
 }