alice starts a session on node-1
  session_start returned HTTP 200, session_id=f49f03e7-95b3-42e7-86cd-68269d96e03e
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=f49f03e7-95b3-42e7-86cd-68269d96e03e
  bob sees 2 rows tagged session_id=f49f03e7-95b3-42e7-86cd-68269d96e03e (expected 2)