- Carry BigInts, Sets, and regular expressions through checked native storage without a JavaScript engine.
- Preserve dictionary aliases, spreads, frozen metadata, and fluent initialization helpers.
- Collect checked object and closure cycles while preserving live references.
- Shard portable coverage across 16 sandboxes while retaining focused Darwin contracts.
- Run invariant suites once and keep differential and sanitizer-sensitive coverage in both lanes.
- Harden sandbox transport, exit-status parsing, and Linux runtime test portability.