alice starts a session on node-1
  session_start returned HTTP 200, session_id=f886d486-5b9a-4450-91a8-2326468ab52d
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=f886d486-5b9a-4450-91a8-2326468ab52d
  bob sees 2 rows tagged session_id=f886d486-5b9a-4450-91a8-2326468ab52d (expected 2)