unreachable_retry.plan_retry parks a cron job at now + ladder delay, an
instant that is off the expression's lattice. The stale-cron guard on the
due scan classified it as a direct schedule edit (STALE_CRON_EXPR_EDIT) and
re-anchored it to the natural occurrence without firing, so the 5/15/30-minute
ladder never ran for cron jobs — the same failure mode the quota-hold recovery
fire had to exempt itself from. Record the ladder instant in the retry state
and let _reanchor_stale_cron accept either planner's parked instant as an
authorized one-shot off-lattice fire; interval jobs and legacy state without
the instant keep the previous behaviour.
3e3cfec49d