alice starts a session on node-1
  session_start returned HTTP 200, session_id=0ed89cb3-c6b1-4b6d-a1ea-ab9d96d1aad7
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=0ed89cb3-c6b1-4b6d-a1ea-ab9d96d1aad7
  bob sees 2 rows tagged session_id=0ed89cb3-c6b1-4b6d-a1ea-ab9d96d1aad7 (expected 2)