alice starts a session on node-1
  session_start returned HTTP 200, session_id=f32b2d4f-541a-4a74-bdd6-6799e3c3b9ba
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=f32b2d4f-541a-4a74-bdd6-6799e3c3b9ba
  bob sees 2 rows tagged session_id=f32b2d4f-541a-4a74-bdd6-6799e3c3b9ba (expected 2)