alice starts a session on node-1
  session_start returned HTTP 200, session_id=07bb9a3e-2e8a-45bb-8ec0-3f853ad8e3b7
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=07bb9a3e-2e8a-45bb-8ec0-3f853ad8e3b7
  bob sees 2 rows tagged session_id=07bb9a3e-2e8a-45bb-8ec0-3f853ad8e3b7 (expected 2)