- Add opt-in raise_on_missing_state flag to kickoff, kickoff_async,
akickoff, stream_events, and astream: when True and the
restore_from_state_id lookup misses (or no persistence backend is
configured), kickoff raises a clear ValueError instead of silently
running a fresh session.
- Expose flow.last_restore_succeeded (None = no restore requested,
True = hydrated, False = miss) so API wrappers can detect silent
restore misses without parsing logs.
- Default behavior is unchanged: misses still fall back silently.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>