alice starts a session on node-1
  session_start returned HTTP 200, session_id=e40bdfe8-37a2-4a09-a112-4a2fc8c11b6e
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=e40bdfe8-37a2-4a09-a112-4a2fc8c11b6e
  bob sees 2 rows tagged session_id=e40bdfe8-37a2-4a09-a112-4a2fc8c11b6e (expected 2)