alice starts a session on node-1
  session_start returned HTTP 200, session_id=444df584-de37-4d84-b98e-1ea113df7488
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=444df584-de37-4d84-b98e-1ea113df7488
  bob sees 2 rows tagged session_id=444df584-de37-4d84-b98e-1ea113df7488 (expected 2)