alice starts a session on node-1
  session_start returned HTTP 200, session_id=2b11cb31-6757-48e0-bbf3-f3307a93f2b3
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=2b11cb31-6757-48e0-bbf3-f3307a93f2b3
  bob sees 2 rows tagged session_id=2b11cb31-6757-48e0-bbf3-f3307a93f2b3 (expected 2)