When dispatchBackupForGroup's conn.Send errors, queue a pending_runs
row (attempt=1, next_attempt_at = now + group.RetryBackoffSeconds)
instead of silently dropping the fire. The orphaned queued job row
is left behind for forensic visibility — the drainer will create a
fresh job row on its retry.
Also adds Store.ListPendingRunsForHost — the on-reconnect drain
walks every row for the host, regardless of due-ness, since the
host being back makes 'due' irrelevant.
steve
194e6c9719