Region-resident scheduling metadata. It owns no file handles or reservations.
Planning works on a private snapshot; the accepted plan consumes one fairness
turn per selected key. Execution success or failure does not rewrite ages.
A work identity survives file replacement and picking epochs, but not a region
incarnation. Different classes in the same window retain independent ages.
Waiting compensation starts after one minute. This is a promotion threshold,
not a deadline: an executing batch is never preempted to run an overdue pick.
It is checked at pick time and does not wake the scheduler on its own.