Durable SessionStore over Redis, modelled on Redis Streams. The conversation is an append-only stream (XADD/XRANGE) so appends are atomic and O(1) with no read-modify-write — concurrent appends never lose an entry. Session metadata (turn state, config template, resume policy) lives in a hash; eager session_ids live in a SET for list_resumable/1.

The handle is {conn, namespace} (the host owns the Redix connection, Oban-style). All of a session's keys share a {sid} hash-tag so multi-key reads/forks stay in one Redis Cluster slot. Opaque values use term_to_binary / binary_to_term(_, [:safe]).

Durability is the operator's Redis config (AOF recommended). For the fail-closed invariant, pass wait: {numreplicas, timeout_ms} so boundary writes block on replica acknowledgement and fail the turn if unmet.