The gate reads t3's state.sqlite: safe to restart only when zero threads have an
active_turn_id AND the most-recent thread activity is older than the quiet buffer
(default 15m). Fail-closed on any parse/query error. Pure-bash unit tests cover
the boundaries against fixture DBs (no root/bats/Docker).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
