alice starts a session on node-1
  session_start returned HTTP 200, session_id=fdae9b19-0b4c-411f-977a-0edaa5f5815d
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=fdae9b19-0b4c-411f-977a-0edaa5f5815d
  bob sees 2 rows tagged session_id=fdae9b19-0b4c-411f-977a-0edaa5f5815d (expected 2)