# Ordering & Inclusion

Order sequencing is deterministic, derived from the Continuum sequencing layer.

#### Continuum Sequence

Every order receives a globally unique sequence number:

```
continuum_sequence = (tick_number << 32) | sequence_in_tick
```

* `tick_number` — Block height from Continuum (VDF-proven)
* `sequence_in_tick` — Position within that tick (0-indexed)

This replaces timestamp-based ordering to ensure all nodes process orders identically.

#### Order Structure

```rust
TickOrder {
    order_id: OrderId,
    market_id: MarketId,
    account_id: AccountId,
    side: Side,                    // Buy | Sell
    price: i64,
    quantity: u64,

    // Sequencing
    tick_number: u64,
    sequence_in_tick: u64,
    continuum_sequence: u64,       // PRIMARY KEY

    // Perpetuals
    leverage: Option<u64>,
    position_effect: Option<PositionEffect>,  // Open | Close
    reduce_only: bool,
    margin_mode: Option<MarginMode>,          // Cross | Isolated
    liquidation: bool,             // System-generated liquidation
}
```

#### Inclusion Rules

1. **Zero-quantity rejection** — Orders with `quantity == 0` are rejected at insertion
2. **Margin validation** — Orders must pass `reserve_margin_for_order()` before inclusion
3. **Signature verification** — All orders are Ed25519-signed; invalid signatures rejected

#### Priority Queue Processing

Orders are processed via a binary min-heap keyed by `continuum_sequence`:

```
price_updates → triggers → regular_orders → liquidations
```

Within each category, earlier sequences execute first (FIFO from Continuum).

#### Cancellation Handling

Cancellations use the same `continuum_sequence` ordering:

```rust
TickCancellation {
    order_id: OrderId,
    continuum_sequence: u64,
}
```

Cancels are processed in sequence order alongside new orders, ensuring deterministic interleaving.

***


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