alice starts a session on node-1
  session_start returned HTTP 200, session_id=213ffcaf-c9ad-4141-9b05-407b2cae07a6
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=213ffcaf-c9ad-4141-9b05-407b2cae07a6
  bob sees 2 rows tagged session_id=213ffcaf-c9ad-4141-9b05-407b2cae07a6 (expected 2)