alice starts a session on node-1
  session_start returned HTTP 200, session_id=f70dfd26-3087-4b12-b23b-8b9e3ccf9a75
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=f70dfd26-3087-4b12-b23b-8b9e3ccf9a75
  bob sees 2 rows tagged session_id=f70dfd26-3087-4b12-b23b-8b9e3ccf9a75 (expected 2)