Repeatability check

Runs each fixture twice with fixed options and verifies stable result metrics.

Waiting to run…

1. Light DOM: pending
2. Nested Shadow DOM: pending
3. Mutation churn: pending
4. Shadow lifecycle: attach: pending
5. Shadow lifecycle: detach: pending
6. Shadow lifecycle: reattach: pending
7. Shadow lifecycle: attachConnected: pending
8. Snapshot size: pending