Spike in Backup Rate causes many conflicts and number of backup agents to drop

When there is a spike in the backup rate, we see an equivalent spike in conflicts. Several backup agents also fail to report to the cluster for a couple of minutes around the spike in backup rate.

Start by reproducing a spike in backup rate and observing the corresponding conflicts and backup-agent reporting in the cluster. Trace the backup-rate handling, conflict behavior, and agent-to-cluster reporting path; done requires identifying the cause and validating a fix against all three reported symptoms.

Written by the indexing model from the issue text.