alice starts a session on node-1
  session_start returned HTTP 200, session_id=8714744c-6954-4dd0-945e-74d682bec36a
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=8714744c-6954-4dd0-945e-74d682bec36a
  bob sees 2 rows tagged session_id=8714744c-6954-4dd0-945e-74d682bec36a (expected 2)