Why: F11 - SQLite runs lost mailbox/handoffs/board across restarts,
identical JSON entries collapsed during decode, and checkpoint or
terminal-save failures were swallowed behind success events.
Evidence: store and checkpoint tests pass incl. injected-failure and
round-trip tables (verify-u8.json, exit=0); schema migration preserves
rows.
Impact: runs survive restarts with collaboration state; save failures
are visible before any completion event; async/on_exit semantics kept.
Refs: feature/agent-stack-audit-remediation-b2 U8