handleRelease cancelled the per-lease renewal goroutine but deleted the
KV entry without waiting for it to exit. An in-flight reaffirm/renew Put
could land after the Delete, re-creating the lease and leaking a KV
record. Add a per-loop done channel and block on it after cancel so any
pending Put completes before the delete, making DrainAll's release path
deterministically synchronous.
Josh Siviour
34badea0d9