The lease maintenance process does not seem robust in the face of garbage-collection-enabled storage servers

[exarkun]

ZKAPAuthorizer automatically renews leases for a set of reachable objects. For a while it tried to do this "shortly" before the leases expired. More recently (#215) it changed to wait at least until the leases expired. If an active lease means "keep this share" then waiting until after the leases expire means storage servers might decided not to keep shares the client still wants.

Additionally, if there is no running Tahoe-LAFS client node with the ZKAPAuthorizer plugin when lease expiration time comes around, there is nothing that will renew the leases.

These issues need to be dealt with so that ZKAPAuthorizer can reliably ensure that shares that are meant to be kept always have an active lease.