Surface pending/calendar_failed booking states in the admin bookings list with
proper status badges (failed shows the last calendar error as a tooltip), and
add an operator "Retry now" action. The retry re-drives the same Stalwart
calendar write (confirm + attendee email on success); for a terminal
calendar_failed booking it re-claims the slot lock atomically first and refuses
if the time was taken in the meantime, so a manual retry can never double-book.
A failed Stalwart calendar write during confirmation no longer deletes the
booking + SlotLock. The booking stays 'pending' with its lock retained, and a
new @Cron worker (every 2 min, max 5 attempts by default) re-drives the write:
on success it promotes to 'confirmed' and sends the confirmation email; after
the cap it moves to the terminal 'calendar_failed' state and releases the lock.
Tracks calendarWriteAttempts + lastCalendarError on the Booking. The public
confirm endpoint still throws 503 on a failed first write (preserving the DoD:
never surface a confirmed booking without a calendar event); the pending row is
left for the background retry to finish.
Ronni Baslund