alice starts a session on node-1
  session_start returned HTTP 200, session_id=2b5b1977-76b3-4e90-bcc3-cf088898800e
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=2b5b1977-76b3-4e90-bcc3-cf088898800e
  bob sees 2 rows tagged session_id=2b5b1977-76b3-4e90-bcc3-cf088898800e (expected 2)