kvserver: only pause followers when holding active lease

If the raft leader is not the leaseholder (which includes the case in
which we just transferred the lease away), leave all followers unpaused.
Otherwise, the leaseholder won't learn that the entries it submitted
were committed which effectively causes range unavailability.

Fixes #84884.

Release note: None

pkg/kv/kvserver/replica_raft_overload.go

@@ -230,6 +230,15 @@ func (r *Replica) updatePausedFollowersLocked(
 		return
 	}
 
+	status := r.leaseStatusAtRLocked(ctx, r.Clock().NowAsClockTimestamp())
+	if !status.IsValid() || status.OwnedBy(r.StoreID()) {
+		// If we're not the leaseholder (which includes the case in which we just
+		// transferred the lease away), leave all followers unpaused. Otherwise, the
+		// leaseholder won't learn that the entries it submitted were committed
+		// which effectively causes range unavailability.
+		return
+	}
+
 	// When multiple followers are overloaded, we may not be able to exclude all
 	// of them from replication traffic due to quorum constraints. We would like
 	// a given Range to deterministically exclude the same store (chosen