alice starts a session on node-1
  session_start returned HTTP 200, session_id=89554cd3-37f4-473d-82cb-491f19f83c47
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=89554cd3-37f4-473d-82cb-491f19f83c47
  bob sees 2 rows tagged session_id=89554cd3-37f4-473d-82cb-491f19f83c47 (expected 2)