alice starts a session on node-1
  session_start returned HTTP 200, session_id=01d82c21-a43e-48e7-b01d-f38c0098b86c
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=01d82c21-a43e-48e7-b01d-f38c0098b86c
  bob sees 2 rows tagged session_id=01d82c21-a43e-48e7-b01d-f38c0098b86c (expected 2)