alice starts a session on node-1
  session_start returned HTTP 200, session_id=3d077ca6-577f-4521-a705-1d077bdf88eb
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=3d077ca6-577f-4521-a705-1d077bdf88eb
  bob sees 2 rows tagged session_id=3d077ca6-577f-4521-a705-1d077bdf88eb (expected 2)