* feat(sandbox): unify command execution and enforcement
* test(sandbox): make platform contracts portable
* fix(sandbox): close execution lifecycle races
Bound retained interactive output, preserve interruption state, and start workspace observation before process launch.
Protect active runtime roots with cross-platform leases, capture transient protected-path creation events, and restore process attributes after PTY fallback.
* fix(sandbox): restore strict macOS isolation
Remove Seatbelt host-local network allowances after native validation showed localhost filters can reach host interfaces.
Track process reap completion so retained sessions cannot signal a stale numeric PID.
