A session key that exists in the store but would be rolled to a fresh
session by the reset policy (daily/idle/suspended) is not an active
session. Treating it as active suppressed the first-turn Slack
thread-history reseed after reset (#55239).
_has_active_session_for_thread() now consults SessionStore._should_reset
so a stale entry gates like a missing one, letting _fetch_thread_context
reseed the fresh session with recent thread history.
Fixes#55239.
Salvaged from #55240 by @ooiuuii.
luyifan
2d71e9e9bc