Margin & leverage

Cross vs isolated

• Cross — a single collateral pool supports every open position. Losses on one symbol eat into margin available to the rest; capital-efficient but correlated risk.
• Isolated — each position owns its own margin slice. A liquidation only burns that slice.

Mode is chosen per symbol and can be switched while flat.

Margin math

• Initial margin = notional / leverage.
• Maintenance margin = notional × mm_rate, where mm_rate depends on the tier (see settlement-substrate/src/margin_tiers.rs).
• Liquidation occurs when equity ≤ maintenance margin. Liquidations are partial when possible (up to the tier boundary).