Auto deleveraging

The liquidator has one last option to avoid liquidations that would cause a sufficiently large drawdown, at which point auto-deleveraging is triggered.

Auto-deleveraging strictly ensures that the platform stays solvent. If a user's account value or isolated position value becomes negative, the users on the opposite side of the position are ranked by unrealized pnl and leverage used. Those traders' positions are closed at the previous oracle price against the now underwater user, ensuring that the platform has no bad debt.

Auto-deleveraging is an important final safeguard on the solvency of the platform. There is a strict invariant that under all operations, a user who has no open positions will not socialize any losses of the platform.