You are a mediator in a dispute over water rights in a trans-boundary river basin involving Country A (upstream industrial), Country B (midstream agricultural), and Country C (downstream arid). Develop a negotiation strategy that addresses the core interests of all three parties rather than their stated positions. Identify potential trade-offs, side payments, or technical solutions that could create a Pareto-optimal outcome. Explain how you would handle deadlocks and ensure the durability of the agreement.