Two people, two machines
This run has two links, one per side. Each of them opens a page that shows that side and nothing of the other: their own words, their own limits, their own agent's brief.
Keep one. Send the other one to whoever is playing the other side. Neither of you writes the other's requirements, and neither of you sees them. When both have confirmed what they wrote, the negotiation starts on its own and you both watch it.
Both links are on this page, so whoever opened it can read both sides if they want to. That is a property of handing out two links on one screen, not a claim we are making — the separation this demonstrates is between the two agents, and that one holds however the links were shared. Keep this page to yourself and open only your own side.