- persisting a session's protocol state after a request now rewrites an
existing record only (Redis SET XX, the memory store likewise) and closes
the local copy when the record is gone
- before, a request that finished after DELETE, a revoked or deleted subject
event or the idle expiry put the record back, and the next request
rehydrated the ended session
- found by plan 19.7-05's TestFanOut (revocation and deletion cases, about
one run in a hundred)