Ephemeral ETS persistence adapter — the default, no-database option.
Reads and high-frequency single-writer-per-conversation writes (append,
fsm_state, summaries) run directly against the named public tables owned by a
dedicated owner process. Per-conversation seq is allocated atomically
with :ets.update_counter/4. Tool-call resolution and suspension expiry — which
may race across processes — are serialized through the owner.
Does not survive a node restart (acceptable for the ephemeral adapter); the Ecto adapter is the durable option.