FN-6596: guard compound engineering debug launches

Guard Compound Engineering debug stage launches against stale stage settings and artifacts.

- Add source-level coverage proving stale enabledStages snapshots do not block registered CE stages, including debug.
- Add dist freshness checks for the disabledStages opt-out launch model so stale compiled plugin artifacts fail fast.
- Mirror newly observed core suite-load flakes in the quarantine ledger and Vitest excludes.

Files changed:
 packages/core/vitest.config.ts                     |  5 ++
 .../src/__tests__/dist-freshness.test.ts           | 38 +++++++++++++++
 .../src/__tests__/stage-launch-guard.test.ts       | 57 ++++++++++++++++++++++
 scripts/lib/test-quarantine.json                   | 10 ++++
 4 files changed, 110 insertions(+)

Fusion-Task-Id: FN-6596

Fusion-Task-Lineage: 3cd75e5f-c6f8-4bde-8202-54eeac82b894

scripts/lib/test-quarantine.json

@@ -30,6 +30,16 @@
       "file": "plugins/fusion-plugin-compound-engineering/src/__tests__/work-bridge.test.ts",
       "reason": "CE broad package verification under NODE_ENV=production fix hit a 10000ms beforeEach hook timeout only in the full @fusion-plugin-examples/compound-engineering lane, while an immediate isolated compound-engineering-node run of work-bridge.test.ts passed in 10.96s. Quarantined per deletion-ratchet policy without hookTimeout increases, retries, or assertion loosening.",
       "quarantinedAt": "2026-06-17"
+    },
+    {
+      "file": "packages/core/src/__tests__/task-list-format.test.ts",
+      "reason": "FN-6596 verification: pnpm test failed in the broad changed-package @fusion/core lane with a beforeEach hook timeout in task-list-format after the merge gate had passed; immediate isolated rerun of the file passed. Quarantined as a suite-load timeout flake without timeout bumps, retries, or assertion loosening.",
+      "quarantinedAt": "2026-06-17"
+    },
+    {
+      "file": "packages/core/src/__tests__/test-project.test.ts",
+      "reason": "FN-6596 verification: pnpm test failed in the broad changed-package @fusion/core lane with a test timeout in test-project after the merge gate had passed; immediate isolated rerun of the file passed. Quarantined as a suite-load timeout flake without timeout bumps, retries, or assertion loosening.",
+      "quarantinedAt": "2026-06-17"
     }
   ]
 }