alice starts a session on node-1
  session_start returned HTTP 200, session_id=7b1f3156-504a-4aba-a4a1-ecd70ee5edde
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=7b1f3156-504a-4aba-a4a1-ecd70ee5edde
  bob sees 2 rows tagged session_id=7b1f3156-504a-4aba-a4a1-ecd70ee5edde (expected 2)