alice starts a session on node-1
  session_start returned HTTP 200, session_id=d7073168-eca0-4eda-8989-5300a48e23f5
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=d7073168-eca0-4eda-8989-5300a48e23f5
  bob sees 2 rows tagged session_id=d7073168-eca0-4eda-8989-5300a48e23f5 (expected 2)