The Difficult Counterpart Handler

Help me negotiate with this difficult counterpart.

Their behaviour: [AGGRESSIVE / DISHONEST / EMOTIONAL / STONEWALLING /
POSITIONAL]
The negotiation and stakes: [DESCRIBE]
My constraints: [WHY I CAN'T JUST WALK, IF I CAN'T]

Provide:
1. How to stay calm and not get pulled into their game
2. How to respond to the specific difficult behaviour
3. How to redirect to interests and problem-solving
4. How to protect myself if they're acting in bad faith
5. When to walk away or bring in another party

Don't react to the difficulty — help me change the game. Flag if their
conduct suggests I need protections in writing.