Hi!

Thanks for the PR.

We need a migration path for existing Redis users before merging this.

With this change, claimDueSchedule() only reads from the new schedules::due ZSET, but users upgrading from the current version will only have the existing schedule hashes plus schedules::index. Those schedules will never be claimed until something manually rewrites them or calls backfillDueIndex().

Can we make the migration automatic/idempotent, or expose and document a required migration step? For example, on startup or first claim, backfill schedules::due from schedules::index for active schedules with next_run_at.