alice starts a session on node-1
  session_start returned HTTP 200, session_id=7063320b-c176-4899-b655-3db7c0dba68d
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=7063320b-c176-4899-b655-3db7c0dba68d
  bob sees 2 rows tagged session_id=7063320b-c176-4899-b655-3db7c0dba68d (expected 2)