Documents the v4.2.0 release window in Keep-a-Changelog format, including prompt gate fixes, internal audits, known issues, and the watchdog supersession history.
Closes LOW-14, LOW-16
Document all 7+ BLOCKER+HIGH fixes, breaking-change-free additions
(public exports), known issue for delegated child-session fallback
(PR #3825 deferred to v4.2.1), and internal-only changes.
Closes L14