Booking reminders and delivery recovery
Replace obsolete reminders, suppress cancelled-booking messages and bound failure recovery.
Replace pending reminders after a booking moves
Recalculate reminder timing from the confirmed schedule revision and retire messages for the old time.
Suppress queued reminders after cancellation
Recheck active booking state immediately before dispatch while retaining already-sent history.
Recover a failed reminder within a bounded useful window
Distinguish failed, unknown and accepted delivery outcomes before another attempt.