Execution Simulator

Responsibilities

Simulates order execution for paper trading (Milestone 1). Replaces a live broker adapter.

• Subscribes to Order events
• Simulates fill at the last known market price (from most recent MarketTick)
• Publishes Execution events with fill price, quantity, and timestamp
• Subscribes to MarketTick to track current prices per symbol

IBrokerAdapter Protocol

The Execution Simulator implements the IBrokerAdapter interface, making it swappable with a live broker adapter in future milestones.

class IBrokerAdapter(Protocol):
    def submit_order(self, order: Order) -> Execution: ...

Event Flow

MarketTick → ExecutionSimulator (price cache)
Order → ExecutionSimulator → Execution (published at last price)

Design Notes

• Paper trading only — no real money or broker connectivity
• Fill price = last MarketTick price for the symbol
• Immediate fill assumed (no partial fills, no slippage model in Milestone 1)

Source

src/components/execution_simulator.py